diff --git a/cmd/mount_zfs.c b/cmd/mount_zfs.c
index 669ed88f9..1f26a3f60 100644
--- a/cmd/mount_zfs.c
+++ b/cmd/mount_zfs.c
@@ -108,20 +108,21 @@ mtab_is_writeable(void)
 }
 
 static int
-mtab_update(char *dataset, char *mntpoint, char *type, char *mntopts)
+mtab_update(const char *dataset, const char *mntpoint, const char *type,
+    const char *mntopts)
 {
 	struct mntent mnt;
 	FILE *fp;
 	int error;
 
-	mnt.mnt_fsname = dataset;
-	mnt.mnt_dir = mntpoint;
-	mnt.mnt_type = type;
-	mnt.mnt_opts = mntopts ? mntopts : "";
+	mnt.mnt_fsname = (char *)dataset;
+	mnt.mnt_dir = (char *)mntpoint;
+	mnt.mnt_type = (char *)type;
+	mnt.mnt_opts = (char *)(mntopts ?: "");
 	mnt.mnt_freq = 0;
 	mnt.mnt_passno = 0;
 
-	fp = setmntent("/etc/mtab", "a+");
+	fp = setmntent("/etc/mtab", "a+e");
 	if (!fp) {
 		(void) fprintf(stderr, gettext(
 		    "filesystem '%s' was mounted, but /etc/mtab "
diff --git a/cmd/raidz_test/raidz_test.c b/cmd/raidz_test/raidz_test.c
index a712b10b3..8b21bc098 100644
--- a/cmd/raidz_test/raidz_test.c
+++ b/cmd/raidz_test/raidz_test.c
@@ -69,7 +69,7 @@ static void sig_handler(int signo)
 
 static void print_opts(raidz_test_opts_t *opts, boolean_t force)
 {
-	char *verbose;
+	const char *verbose;
 	switch (opts->rto_v) {
 		case D_ALL:
 			verbose = "no";
diff --git a/cmd/zdb/zdb.c b/cmd/zdb/zdb.c
index ce95759dc..d3a68171a 100644
--- a/cmd/zdb/zdb.c
+++ b/cmd/zdb/zdb.c
@@ -102,7 +102,7 @@
 #define	ZDB_MAP_OBJECT_ID(obj) (obj)
 #endif
 
-static char *
+static const char *
 zdb_ot_name(dmu_object_type_t type)
 {
 	if (type < DMU_OT_NUMTYPES)
@@ -2922,7 +2922,7 @@ dsl_deadlist_entry_dump(void *arg, dsl_deadlist_entry_t *dle)
 }
 
 static void
-dump_blkptr_list(dsl_deadlist_t *dl, char *name)
+dump_blkptr_list(dsl_deadlist_t *dl, const char *name)
 {
 	char bytes[32];
 	char comp[32];
@@ -2963,7 +2963,7 @@ dump_blkptr_list(dsl_deadlist_t *dl, char *name)
 	if (dump_opt['d'] < 4)
 		return;
 
-	(void) printf("\n");
+	(void) putchar('\n');
 
 	dsl_deadlist_iterate(dl, dsl_deadlist_entry_dump, NULL);
 }
@@ -3098,9 +3098,8 @@ static void
 print_idstr(uint64_t id, const char *id_type)
 {
 	if (FUID_INDEX(id)) {
-		char *domain;
-
-		domain = zfs_fuid_idx_domain(&idx_tree, FUID_INDEX(id));
+		const char *domain =
+		    zfs_fuid_idx_domain(&idx_tree, FUID_INDEX(id));
 		(void) printf("\t%s     %llx [%s-%d]\n", id_type,
 		    (u_longlong_t)id, domain, (int)FUID_RID(id));
 	} else {
@@ -3643,7 +3642,7 @@ count_ds_mos_objects(dsl_dataset_t *ds)
 	}
 }
 
-static const char *objset_types[DMU_OST_NUMTYPES] = {
+static const char *const objset_types[DMU_OST_NUMTYPES] = {
 	"NONE", "META", "ZPL", "ZVOL", "OTHER", "ANY" };
 
 /*
@@ -3653,7 +3652,7 @@ static const char *objset_types[DMU_OST_NUMTYPES] = {
  * pointer to point to a descriptive error message.
  */
 static int
-parse_object_range(char *range, zopt_object_range_t *zor, char **msg)
+parse_object_range(char *range, zopt_object_range_t *zor, const char **msg)
 {
 	uint64_t flags = 0;
 	char *p, *s, *dup, *flagstr, *tmp = NULL;
@@ -4236,13 +4235,13 @@ first_label(cksum_record_t *rec)
 }
 
 static void
-print_label_numbers(char *prefix, cksum_record_t *rec)
+print_label_numbers(const char *prefix, const cksum_record_t *rec)
 {
-	printf("%s", prefix);
+	fputs(prefix, stdout);
 	for (int i = 0; i < VDEV_LABELS; i++)
 		if (rec->labels[i] == B_TRUE)
 			printf("%d ", i);
-	printf("\n");
+	putchar('\n');
 }
 
 #define	MAX_UBERBLOCK_COUNT (VDEV_UBERBLOCK_RING >> UBERBLOCK_SHIFT)
@@ -5126,7 +5125,7 @@ same_metaslab(spa_t *spa, uint64_t vdev, uint64_t off1, uint64_t off2)
  * Used to simplify reporting of the histogram data.
  */
 typedef struct one_histo {
-	char *name;
+	const char *name;
 	uint64_t *count;
 	uint64_t *len;
 	uint64_t cumulative;
@@ -8093,32 +8092,33 @@ zdb_read_block(char *thing, spa_t *spa)
 	vdev_t *vd;
 	abd_t *pabd;
 	void *lbuf, *buf;
-	char *s, *p, *dup, *vdev, *flagstr, *sizes, *tmp = NULL;
+	char *s, *p, *dup, *flagstr, *sizes, *tmp = NULL;
+	const char *vdev, *errmsg = NULL;
 	int i, error;
 	boolean_t borrowed = B_FALSE, found = B_FALSE;
 
 	dup = strdup(thing);
 	s = strtok_r(dup, ":", &tmp);
-	vdev = s ? s : "";
+	vdev = s ?: "";
 	s = strtok_r(NULL, ":", &tmp);
 	offset = strtoull(s ? s : "", NULL, 16);
 	sizes = strtok_r(NULL, ":", &tmp);
 	s = strtok_r(NULL, ":", &tmp);
-	flagstr = strdup(s ? s : "");
+	flagstr = strdup(s ?: "");
 
-	s = NULL;
-	tmp = NULL;
 	if (!zdb_parse_block_sizes(sizes, &lsize, &psize))
-		s = "invalid size(s)";
+		errmsg = "invalid size(s)";
 	if (!IS_P2ALIGNED(psize, DEV_BSIZE) || !IS_P2ALIGNED(lsize, DEV_BSIZE))
-		s = "size must be a multiple of sector size";
+		errmsg = "size must be a multiple of sector size";
 	if (!IS_P2ALIGNED(offset, DEV_BSIZE))
-		s = "offset must be a multiple of sector size";
-	if (s) {
-		(void) printf("Invalid block specifier: %s  - %s\n", thing, s);
+		errmsg = "offset must be a multiple of sector size";
+	if (errmsg) {
+		(void) printf("Invalid block specifier: %s  - %s\n",
+		    thing, errmsg);
 		goto done;
 	}
 
+	tmp = NULL;
 	for (s = strtok_r(flagstr, ":", &tmp);
 	    s != NULL;
 	    s = strtok_r(NULL, ":", &tmp)) {
@@ -8930,13 +8930,13 @@ retry_lookup:
 			    sizeof (zopt_object_range_t));
 			for (unsigned i = 0; i < zopt_object_args; i++) {
 				int err;
-				char *msg = NULL;
+				const char *msg = NULL;
 
 				err = parse_object_range(argv[i],
 				    &zopt_object_ranges[i], &msg);
 				if (err != 0)
 					fatal("Bad object or range: '%s': %s\n",
-					    argv[i], msg ? msg : "");
+					    argv[i], msg ?: "");
 			}
 		} else if (argc > 0 && dump_opt['m']) {
 			zopt_metaslab_args = argc;
diff --git a/cmd/zed/agents/fmd_api.c b/cmd/zed/agents/fmd_api.c
index e7eff16fd..af78eb74c 100644
--- a/cmd/zed/agents/fmd_api.c
+++ b/cmd/zed/agents/fmd_api.c
@@ -389,7 +389,8 @@ zed_log_fault(nvlist_t *nvl, const char *uuid, const char *code)
 static const char *
 fmd_fault_mkcode(nvlist_t *fault)
 {
-	char *class, *code = "-";
+	char *class;
+	const char *code = "-";
 
 	/*
 	 * Note: message codes come from: openzfs/usr/src/cmd/fm/dicts/ZFS.po
diff --git a/cmd/zfs/zfs_main.c b/cmd/zfs/zfs_main.c
index e29dfa57d..1a2106c2e 100644
--- a/cmd/zfs/zfs_main.c
+++ b/cmd/zfs/zfs_main.c
@@ -471,7 +471,7 @@ safe_realloc(void *data, size_t size)
 }
 
 static char *
-safe_strdup(char *str)
+safe_strdup(const char *str)
 {
 	char *dupstr = strdup(str);
 
@@ -690,7 +690,8 @@ parse_depth(char *opt, int *flags)
 
 #define	PROGRESS_DELAY 2		/* seconds */
 
-static char *pt_reverse = "\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b";
+static const char *pt_reverse =
+	"\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b";
 static time_t pt_begin;
 static char *pt_header = NULL;
 static boolean_t pt_shown;
@@ -703,7 +704,7 @@ start_progress_timer(void)
 }
 
 static void
-set_progress_header(char *header)
+set_progress_header(const char *header)
 {
 	assert(pt_header == NULL);
 	pt_header = safe_strdup(header);
@@ -714,7 +715,7 @@ set_progress_header(char *header)
 }
 
 static void
-update_progress(char *update)
+update_progress(const char *update)
 {
 	if (!pt_shown && time(NULL) > pt_begin) {
 		int len = strlen(update);
@@ -732,10 +733,10 @@ update_progress(char *update)
 }
 
 static void
-finish_progress(char *done)
+finish_progress(const char *done)
 {
 	if (pt_shown) {
-		(void) printf("%s\n", done);
+		(void) puts(done);
 		(void) fflush(stdout);
 	}
 	free(pt_header);
@@ -1903,8 +1904,8 @@ get_callback(zfs_handle_t *zhp, void *data)
 	nvlist_t *user_props = zfs_get_user_props(zhp);
 	zprop_list_t *pl = cbp->cb_proplist;
 	nvlist_t *propval;
-	char *strval;
-	char *sourceval;
+	const char *strval;
+	const char *sourceval;
 	boolean_t received = is_recvd_column(cbp);
 
 	for (; pl != NULL; pl = pl->pl_next) {
@@ -1973,10 +1974,10 @@ get_callback(zfs_handle_t *zhp, void *data)
 				sourcetype = ZPROP_SRC_NONE;
 				strval = "-";
 			} else {
-				verify(nvlist_lookup_string(propval,
-				    ZPROP_VALUE, &strval) == 0);
-				verify(nvlist_lookup_string(propval,
-				    ZPROP_SOURCE, &sourceval) == 0);
+				strval = fnvlist_lookup_string(propval,
+				    ZPROP_VALUE);
+				sourceval = fnvlist_lookup_string(propval,
+				    ZPROP_SOURCE);
 
 				if (strcmp(sourceval,
 				    zfs_get_name(zhp)) == 0) {
@@ -2618,9 +2619,9 @@ enum us_field_types {
 	USFIELD_OBJUSED,
 	USFIELD_OBJQUOTA
 };
-static char *us_field_hdr[] = { "TYPE", "NAME", "USED", "QUOTA",
+static const char *const us_field_hdr[] = { "TYPE", "NAME", "USED", "QUOTA",
 				    "OBJUSED", "OBJQUOTA" };
-static char *us_field_names[] = { "type", "name", "used", "quota",
+static const char *const us_field_names[] = { "type", "name", "used", "quota",
 				    "objused", "objquota" };
 #define	USFIELD_LAST	(sizeof (us_field_names) / sizeof (char *))
 
@@ -2640,8 +2641,8 @@ static int us_type_bits[] = {
 	USTYPE_SMB_USR,
 	USTYPE_ALL
 };
-static char *us_type_names[] = { "posixgroup", "posixuser", "smbgroup",
-	"smbuser", "all" };
+static const char *const us_type_names[] = { "posixgroup", "posixuser",
+	"smbgroup", "smbuser", "all" };
 
 typedef struct us_node {
 	nvlist_t	*usn_nvl;
@@ -2669,11 +2670,9 @@ typedef struct {
 } us_sort_info_t;
 
 static int
-us_field_index(char *field)
+us_field_index(const char *field)
 {
-	int i;
-
-	for (i = 0; i < USFIELD_LAST; i++) {
+	for (int i = 0; i < USFIELD_LAST; i++) {
 		if (strcmp(field, us_field_names[i]) == 0)
 			return (i);
 	}
@@ -2695,8 +2694,8 @@ us_compare(const void *larg, const void *rarg, void *unused)
 	boolean_t lvb, rvb;
 
 	for (; sortcol != NULL; sortcol = sortcol->sc_next) {
-		char *lvstr = "";
-		char *rvstr = "";
+		char *lvstr = (char *)"";
+		char *rvstr = (char *)"";
 		uint32_t lv32 = 0;
 		uint32_t rv32 = 0;
 		uint64_t lv64 = 0;
@@ -2818,7 +2817,7 @@ userspace_cb(void *arg, const char *domain, uid_t rid, uint64_t space)
 	us_cbdata_t *cb = (us_cbdata_t *)arg;
 	zfs_userquota_prop_t prop = cb->cb_prop;
 	char *name = NULL;
-	char *propname;
+	const char *propname;
 	char sizebuf[32];
 	us_node_t *node;
 	uu_avl_pool_t *avl_pool = cb->cb_avl_pool;
@@ -3018,26 +3017,25 @@ print_us_node(boolean_t scripted, boolean_t parsable, int *fields, int types,
 	while ((field = fields[cfield]) != USFIELD_LAST) {
 		nvpair_t *nvp = NULL;
 		data_type_t type;
-		uint32_t val32;
-		uint64_t val64;
-		char *strval = "-";
+		uint32_t val32 = -1;
+		uint64_t val64 = -1;
+		const char *strval = "-";
 
-		while ((nvp = nvlist_next_nvpair(nvl, nvp)) != NULL) {
+		while ((nvp = nvlist_next_nvpair(nvl, nvp)) != NULL)
 			if (strcmp(nvpair_name(nvp),
 			    us_field_names[field]) == 0)
 				break;
-		}
 
 		type = nvp == NULL ? DATA_TYPE_UNKNOWN : nvpair_type(nvp);
 		switch (type) {
 		case DATA_TYPE_UINT32:
-			(void) nvpair_value_uint32(nvp, &val32);
+			val32 = fnvpair_value_uint32(nvp);
 			break;
 		case DATA_TYPE_UINT64:
-			(void) nvpair_value_uint64(nvp, &val64);
+			val64 = fnvpair_value_uint64(nvp);
 			break;
 		case DATA_TYPE_STRING:
-			(void) nvpair_value_string(nvp, &strval);
+			strval = fnvpair_value_string(nvp);
 			break;
 		case DATA_TYPE_UNKNOWN:
 			break;
@@ -3048,7 +3046,7 @@ print_us_node(boolean_t scripted, boolean_t parsable, int *fields, int types,
 		switch (field) {
 		case USFIELD_TYPE:
 			if (type == DATA_TYPE_UINT32)
-				strval = (char *)us_type2str(val32);
+				strval = us_type2str(val32);
 			break;
 		case USFIELD_NAME:
 			if (type == DATA_TYPE_UINT64) {
@@ -3095,12 +3093,12 @@ print_us_node(boolean_t scripted, boolean_t parsable, int *fields, int types,
 
 		if (!first) {
 			if (scripted)
-				(void) printf("\t");
+				(void) putchar('\t');
 			else
-				(void) printf("  ");
+				(void) fputs("  ", stdout);
 		}
 		if (scripted)
-			(void) printf("%s", strval);
+			(void) fputs(strval, stdout);
 		else if (field == USFIELD_TYPE || field == USFIELD_NAME)
 			(void) printf("%-*s", (int)width[field], strval);
 		else
@@ -3110,7 +3108,7 @@ print_us_node(boolean_t scripted, boolean_t parsable, int *fields, int types,
 		cfield++;
 	}
 
-	(void) printf("\n");
+	(void) putchar('\n');
 }
 
 static void
@@ -3476,15 +3474,15 @@ print_dataset(zfs_handle_t *zhp, list_cbdata_t *cb)
 	char property[ZFS_MAXPROPLEN];
 	nvlist_t *userprops = zfs_get_user_props(zhp);
 	nvlist_t *propval;
-	char *propstr;
+	const char *propstr;
 	boolean_t right_justify;
 
 	for (; pl != NULL; pl = pl->pl_next) {
 		if (!first) {
 			if (cb->cb_scripted)
-				(void) printf("\t");
+				(void) putchar('\t');
 			else
-				(void) printf("  ");
+				(void) fputs("  ", stdout);
 		} else {
 			first = B_FALSE;
 		}
@@ -3521,8 +3519,8 @@ print_dataset(zfs_handle_t *zhp, list_cbdata_t *cb)
 			    pl->pl_user_prop, &propval) != 0)
 				propstr = "-";
 			else
-				verify(nvlist_lookup_string(propval,
-				    ZPROP_VALUE, &propstr) == 0);
+				propstr = fnvlist_lookup_string(propval,
+				    ZPROP_VALUE);
 			right_justify = B_FALSE;
 		}
 
@@ -3532,14 +3530,14 @@ print_dataset(zfs_handle_t *zhp, list_cbdata_t *cb)
 		 * format specifier.
 		 */
 		if (cb->cb_scripted || (pl->pl_next == NULL && !right_justify))
-			(void) printf("%s", propstr);
+			(void) fputs(propstr, stdout);
 		else if (right_justify)
 			(void) printf("%*s", (int)pl->pl_width, propstr);
 		else
 			(void) printf("%-*s", (int)pl->pl_width, propstr);
 	}
 
-	(void) printf("\n");
+	(void) putchar('\n');
 }
 
 /*
@@ -6419,7 +6417,7 @@ print_holds(boolean_t scripted, int nwidth, int tagwidth, nvlist_t *nvl)
 {
 	int i;
 	nvpair_t *nvp = NULL;
-	char *hdr_cols[] = { "NAME", "TAG", "TIMESTAMP" };
+	const char *const hdr_cols[] = { "NAME", "TAG", "TIMESTAMP" };
 	const char *col;
 
 	if (!scripted) {
@@ -6607,7 +6605,7 @@ typedef struct get_all_state {
 static int
 get_one_dataset(zfs_handle_t *zhp, void *data)
 {
-	static char *spin[] = { "-", "\\", "|", "/" };
+	static const char *const spin[] = { "-", "\\", "|", "/" };
 	static int spinval = 0;
 	static int spincheck = 0;
 	static time_t last_spin_time = (time_t)0;
@@ -6893,10 +6891,7 @@ share_mount_one(zfs_handle_t *zhp, int op, int flags, enum sa_protocol protocol,
 		break;
 
 	case OP_MOUNT:
-		if (options == NULL)
-			mnt.mnt_mntopts = "";
-		else
-			mnt.mnt_mntopts = (char *)options;
+		mnt.mnt_mntopts = (char *)(options ?: "");
 
 		if (!hasmntopt(&mnt, MNTOPT_REMOUNT) &&
 		    zfs_is_mounted(zhp, NULL)) {
@@ -7616,7 +7611,7 @@ zfs_do_unshare(int argc, char **argv)
 }
 
 static int
-find_command_idx(char *command, int *idx)
+find_command_idx(const char *command, int *idx)
 {
 	int i;
 
@@ -7881,7 +7876,6 @@ static int
 zfs_do_channel_program(int argc, char **argv)
 {
 	int ret, fd, c;
-	char *progbuf, *filename, *poolname;
 	size_t progsize, progread;
 	nvlist_t *outnvl = NULL;
 	uint64_t instrlimit = ZCP_DEFAULT_INSTRLIMIT;
@@ -7938,8 +7932,8 @@ zfs_do_channel_program(int argc, char **argv)
 		goto usage;
 	}
 
-	poolname = argv[0];
-	filename = argv[1];
+	const char *poolname = argv[0];
+	const char *filename = argv[1];
 	if (strcmp(filename, "-") == 0) {
 		fd = 0;
 		filename = "standard input";
@@ -7964,7 +7958,7 @@ zfs_do_channel_program(int argc, char **argv)
 	 */
 	progread = 0;
 	progsize = 1024;
-	progbuf = safe_malloc(progsize);
+	char *progbuf = safe_malloc(progsize);
 	do {
 		ret = read(fd, progbuf + progread, progsize - progread);
 		progread += ret;
@@ -8010,14 +8004,17 @@ zfs_do_channel_program(int argc, char **argv)
 		 * exists.  Otherwise, generate an appropriate error message,
 		 * falling back on strerror() for an unexpected return code.
 		 */
-		char *errstring = NULL;
+		const char *errstring = NULL;
 		const char *msg = gettext("Channel program execution failed");
 		uint64_t instructions = 0;
 		if (outnvl != NULL && nvlist_exists(outnvl, ZCP_RET_ERROR)) {
+			char *es = NULL;
 			(void) nvlist_lookup_string(outnvl,
-			    ZCP_RET_ERROR, &errstring);
-			if (errstring == NULL)
+			    ZCP_RET_ERROR, &es);
+			if (es == NULL)
 				errstring = strerror(ret);
+			else
+				errstring = es;
 			if (ret == ETIME) {
 				(void) nvlist_lookup_uint64(outnvl,
 				    ZCP_ARG_INSTRLIMIT, &instructions);
@@ -8601,7 +8598,7 @@ main(int argc, char **argv)
 {
 	int ret = 0;
 	int i = 0;
-	char *cmdname;
+	const char *cmdname;
 	char **newargv;
 
 	(void) setlocale(LC_ALL, "");
diff --git a/cmd/zpool/zpool_iter.c b/cmd/zpool/zpool_iter.c
index ec3f768e3..a08f27992 100644
--- a/cmd/zpool/zpool_iter.c
+++ b/cmd/zpool/zpool_iter.c
@@ -442,9 +442,8 @@ static void
 vdev_run_cmd(vdev_cmd_data_t *data, char *cmd)
 {
 	int rc;
-	char *argv[2] = {cmd, 0};
-	char *env[5] = {"PATH=/bin:/sbin:/usr/bin:/usr/sbin", NULL, NULL, NULL,
-	    NULL};
+	char *argv[2] = {cmd};
+	char *env[5] = {(char *)"PATH=/bin:/sbin:/usr/bin:/usr/sbin"};
 	char **lines = NULL;
 	int lines_cnt = 0;
 	int i;
diff --git a/cmd/zpool/zpool_main.c b/cmd/zpool/zpool_main.c
index a0aeb8c06..c59829152 100644
--- a/cmd/zpool/zpool_main.c
+++ b/cmd/zpool/zpool_main.c
@@ -711,7 +711,7 @@ print_vdev_tree(zpool_handle_t *zhp, const char *name, nvlist_t *nv, int indent,
 
 	for (c = 0; c < children; c++) {
 		uint64_t is_log = B_FALSE, is_hole = B_FALSE;
-		char *class = "";
+		char *class = (char *)"";
 
 		(void) nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_IS_HOLE,
 		    &is_hole);
@@ -723,7 +723,7 @@ print_vdev_tree(zpool_handle_t *zhp, const char *name, nvlist_t *nv, int indent,
 		(void) nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_IS_LOG,
 		    &is_log);
 		if (is_log)
-			class = VDEV_ALLOC_BIAS_LOG;
+			class = (char *)VDEV_ALLOC_BIAS_LOG;
 		(void) nvlist_lookup_string(child[c],
 		    ZPOOL_CONFIG_ALLOCATION_BIAS, &class);
 		if (strcmp(match, class) != 0)
@@ -804,7 +804,7 @@ prop_list_contains_feature(nvlist_t *proplist)
  * Add a property pair (name, string-value) into a property nvlist.
  */
 static int
-add_prop_list(const char *propname, char *propval, nvlist_t **props,
+add_prop_list(const char *propname, const char *propval, nvlist_t **props,
     boolean_t poolprop)
 {
 	zpool_prop_t prop = ZPOOL_PROP_INVAL;
@@ -905,7 +905,8 @@ add_prop_list(const char *propname, char *propval, nvlist_t **props,
  * Set a default property pair (name, string-value) in a property nvlist
  */
 static int
-add_prop_list_default(const char *propname, char *propval, nvlist_t **props)
+add_prop_list_default(const char *propname, const char *propval,
+    nvlist_t **props)
 {
 	char *pval;
 
@@ -2069,15 +2070,13 @@ typedef struct status_cbdata {
 } status_cbdata_t;
 
 /* Return 1 if string is NULL, empty, or whitespace; return 0 otherwise. */
-static int
-is_blank_str(char *str)
+static boolean_t
+is_blank_str(const char *str)
 {
-	while (str != NULL && *str != '\0') {
+	for (; str != NULL && *str != '\0'; ++str)
 		if (!isblank(*str))
-			return (0);
-		str++;
-	}
-	return (1);
+			return (B_FALSE);
+	return (B_TRUE);
 }
 
 /* Print command output lines for specific vdev in a specific pool */
@@ -2086,7 +2085,7 @@ zpool_print_cmd(vdev_cmd_data_list_t *vcdl, const char *pool, char *path)
 {
 	vdev_cmd_data_t *data;
 	int i, j;
-	char *val;
+	const char *val;
 
 	for (i = 0; i < vcdl->count; i++) {
 		if ((strcmp(vcdl->data[i].path, path) != 0) ||
@@ -2117,17 +2116,17 @@ zpool_print_cmd(vdev_cmd_data_list_t *vcdl, const char *pool, char *path)
 
 			printf("%*s", vcdl->uniq_cols_width[j], val);
 			if (j < vcdl->uniq_cols_cnt - 1)
-				printf("  ");
+				fputs("  ", stdout);
 		}
 
 		/* Print out any values that aren't in a column at the end */
 		for (j = data->cols_cnt; j < data->lines_cnt; j++) {
 			/* Did we have any columns?  If so print a spacer. */
 			if (vcdl->uniq_cols_cnt > 0)
-				printf("  ");
+				fputs("  ", stdout);
 
 			val = data->lines[j];
-			printf("%s", val ? val : "");
+			fputs(val ?: "", stdout);
 		}
 		break;
 	}
@@ -2240,7 +2239,7 @@ print_status_trim(vdev_stat_t *vs, boolean_t verbose)
  * Return the color associated with a health string.  This includes returning
  * NULL for no color change.
  */
-static char *
+static const char *
 health_str_to_color(const char *health)
 {
 	if (strcmp(health, gettext("FAULTED")) == 0 ||
@@ -2276,7 +2275,7 @@ print_status_config(zpool_handle_t *zhp, status_cbdata_t *cb, const char *name,
 	const char *state;
 	char *type;
 	char *path = NULL;
-	char *rcolor = NULL, *wcolor = NULL, *ccolor = NULL;
+	const char *rcolor = NULL, *wcolor = NULL, *ccolor = NULL;
 
 	if (nvlist_lookup_nvlist_array(nv, ZPOOL_CONFIG_CHILDREN,
 	    &child, &children) != 0)
@@ -2318,13 +2317,13 @@ print_status_config(zpool_handle_t *zhp, status_cbdata_t *cb, const char *name,
 			ccolor = ANSI_RED;
 
 		if (cb->cb_literal) {
-			printf(" ");
+			fputc(' ', stdout);
 			printf_color(rcolor, "%5llu",
 			    (u_longlong_t)vs->vs_read_errors);
-			printf(" ");
+			fputc(' ', stdout);
 			printf_color(wcolor, "%5llu",
 			    (u_longlong_t)vs->vs_write_errors);
-			printf(" ");
+			fputc(' ', stdout);
 			printf_color(ccolor, "%5llu",
 			    (u_longlong_t)vs->vs_checksum_errors);
 		} else {
@@ -2332,11 +2331,11 @@ print_status_config(zpool_handle_t *zhp, status_cbdata_t *cb, const char *name,
 			zfs_nicenum(vs->vs_write_errors, wbuf, sizeof (wbuf));
 			zfs_nicenum(vs->vs_checksum_errors, cbuf,
 			    sizeof (cbuf));
-			printf(" ");
+			fputc(' ', stdout);
 			printf_color(rcolor, "%5s", rbuf);
-			printf(" ");
+			fputc(' ', stdout);
 			printf_color(wcolor, "%5s", wbuf);
-			printf(" ");
+			fputc(' ', stdout);
 			printf_color(ccolor, "%5s", cbuf);
 		}
 		if (cb->cb_print_slow_ios) {
@@ -2671,7 +2670,7 @@ print_class_vdevs(zpool_handle_t *zhp, status_cbdata_t *cb, nvlist_t *nv,
 		    &is_log);
 
 		if (is_log) {
-			bias = VDEV_ALLOC_CLASS_LOGS;
+			bias = (char *)VDEV_ALLOC_CLASS_LOGS;
 		} else {
 			(void) nvlist_lookup_string(child[c],
 			    ZPOOL_CONFIG_ALLOCATION_BIAS, &bias);
@@ -2711,8 +2710,8 @@ show_import(nvlist_t *config, boolean_t report_error)
 	char *name;
 	uint64_t guid;
 	uint64_t hostid = 0;
-	char *msgid;
-	char *hostname = "unknown";
+	const char *msgid;
+	const char *hostname = "unknown";
 	nvlist_t *nvroot, *nvinfo;
 	zpool_status_t reason;
 	zpool_errata_t errata;
@@ -3252,7 +3251,7 @@ import_pools(nvlist_t *pools, nvlist_t *props, char *mntopts, int flags,
 			if (first)
 				first = B_FALSE;
 			else if (!do_all)
-				(void) putchar('\n');
+				(void) fputc('\n', stdout);
 
 			if (do_all) {
 				err |= do_import(config, NULL, mntopts,
@@ -4848,7 +4847,7 @@ children:
 			(void) nvlist_lookup_uint64(newchild[c],
 			    ZPOOL_CONFIG_IS_LOG, &islog);
 			if (islog) {
-				bias = VDEV_ALLOC_CLASS_LOGS;
+				bias = (char *)VDEV_ALLOC_CLASS_LOGS;
 			} else {
 				(void) nvlist_lookup_string(newchild[c],
 				    ZPOOL_CONFIG_ALLOCATION_BIAS, &bias);
@@ -5382,7 +5381,7 @@ terminal_height(void)
 static void
 print_zpool_script_help(char *name, char *path)
 {
-	char *argv[] = {path, "-h", NULL};
+	char *argv[] = {path, (char *)"-h", NULL};
 	char **lines = NULL;
 	int lines_cnt = 0;
 	int rc;
@@ -5434,7 +5433,7 @@ print_zpool_dir_scripts(char *dirpath)
  * Print out help text for all zpool status/iostat -c scripts.
  */
 static void
-print_zpool_script_list(char *subcommand)
+print_zpool_script_list(const char *subcommand)
 {
 	char *dir, *sp, *tmp;
 
@@ -5979,7 +5978,7 @@ print_pool(zpool_handle_t *zhp, list_cbdata_t *cb)
 	zprop_list_t *pl = cb->cb_proplist;
 	boolean_t first = B_TRUE;
 	char property[ZPOOL_MAXPROPLEN];
-	char *propstr;
+	const char *propstr;
 	boolean_t right_justify;
 	size_t width;
 
@@ -6214,7 +6213,7 @@ print_list_stats(zpool_handle_t *zhp, const char *name, nvlist_t *nv,
 
 			if (nvlist_lookup_uint64(child[c], ZPOOL_CONFIG_IS_LOG,
 			    &islog) == 0 && islog) {
-				bias = VDEV_ALLOC_CLASS_LOGS;
+				bias = (char *)VDEV_ALLOC_CLASS_LOGS;
 			} else {
 				(void) nvlist_lookup_string(child[c],
 				    ZPOOL_CONFIG_ALLOCATION_BIAS, &bias);
@@ -8118,7 +8117,7 @@ status_callback(zpool_handle_t *zhp, void *data)
 {
 	status_cbdata_t *cbp = data;
 	nvlist_t *config, *nvroot;
-	char *msgid;
+	const char *msgid;
 	zpool_status_t reason;
 	zpool_errata_t errata;
 	const char *health;
@@ -8163,12 +8162,12 @@ status_callback(zpool_handle_t *zhp, void *data)
 	printf("  ");
 	printf_color(ANSI_BOLD, gettext("pool:"));
 	printf(" %s\n", zpool_get_name(zhp));
-	printf(" ");
+	fputc(' ', stdout);
 	printf_color(ANSI_BOLD, gettext("state: "));
 
 	printf_color(health_str_to_color(health), "%s", health);
 
-	printf("\n");
+	fputc('\n', stdout);
 
 	switch (reason) {
 	case ZPOOL_STATUS_MISSING_DEV_R:
@@ -10485,8 +10484,8 @@ print_wait_status_row(wait_data_t *wd, zpool_handle_t *zhp, int row)
 	pool_checkpoint_stat_t *pcs = NULL;
 	pool_scan_stat_t *pss = NULL;
 	pool_removal_stat_t *prs = NULL;
-	char *headers[] = {"DISCARD", "FREE", "INITIALIZE", "REPLACE",
-	    "REMOVE", "RESILVER", "SCRUB", "TRIM"};
+	const char *const headers[] = {"DISCARD", "FREE", "INITIALIZE",
+	    "REPLACE", "REMOVE", "RESILVER", "SCRUB", "TRIM"};
 	int col_widths[ZPOOL_WAIT_NUM_ACTIVITIES];
 
 	/* Calculate the width of each column */
@@ -10508,7 +10507,7 @@ print_wait_status_row(wait_data_t *wd, zpool_handle_t *zhp, int row)
 			if (wd->wd_enabled[i])
 				(void) printf("%*s", col_widths[i], headers[i]);
 		}
-		(void) printf("\n");
+		(void) fputc('\n', stdout);
 	}
 
 	/* Bytes of work remaining in each activity */
@@ -10795,11 +10794,9 @@ found:;
 }
 
 static int
-find_command_idx(char *command, int *idx)
+find_command_idx(const char *command, int *idx)
 {
-	int i;
-
-	for (i = 0; i < NCOMMAND; i++) {
+	for (int i = 0; i < NCOMMAND; ++i) {
 		if (command_table[i].name == NULL)
 			continue;
 
diff --git a/cmd/zpool/zpool_vdev.c b/cmd/zpool/zpool_vdev.c
index 0653a09fa..a7ab36d0b 100644
--- a/cmd/zpool/zpool_vdev.c
+++ b/cmd/zpool/zpool_vdev.c
@@ -274,7 +274,7 @@ make_leaf_vdev(nvlist_t *props, const char *arg, boolean_t is_primary)
 	char path[MAXPATHLEN];
 	struct stat64 statbuf;
 	nvlist_t *vdev = NULL;
-	char *type = NULL;
+	const char *type = NULL;
 	boolean_t wholedisk = B_FALSE;
 	uint64_t ashift = 0;
 	int err;
diff --git a/cmd/zpool_influxdb/zpool_influxdb.c b/cmd/zpool_influxdb/zpool_influxdb.c
index 57bb2ee7b..251d588d8 100644
--- a/cmd/zpool_influxdb/zpool_influxdb.c
+++ b/cmd/zpool_influxdb/zpool_influxdb.c
@@ -90,7 +90,7 @@ char metric_data_type = 'u';
 uint64_t metric_value_mask = UINT64_MAX;
 uint64_t timestamp = 0;
 int complained_about_sync = 0;
-char *tags = "";
+const char *tags = "";
 
 typedef int (*stat_printer_f)(nvlist_t *, const char *, const char *);
 
@@ -131,7 +131,7 @@ escape_string(const char *s)
  * print key=value where value is a uint64_t
  */
 static void
-print_kv(char *key, uint64_t value)
+print_kv(const char *key, uint64_t value)
 {
 	printf("%s=%llu%c", key,
 	    (u_longlong_t)value & metric_value_mask, metric_data_type);
@@ -152,9 +152,9 @@ print_scan_status(nvlist_t *nvroot, const char *pool_name)
 	uint64_t remaining_time;
 	pool_scan_stat_t *ps = NULL;
 	double pct_done;
-	char *state[DSS_NUM_STATES] = {
+	const char *const state[DSS_NUM_STATES] = {
 	    "none", "scanning", "finished", "canceled"};
-	char *func;
+	const char *func;
 
 	(void) nvlist_lookup_uint64_array(nvroot,
 	    ZPOOL_CONFIG_SCAN_STATS,
@@ -262,17 +262,15 @@ static char *
 get_vdev_name(nvlist_t *nvroot, const char *parent_name)
 {
 	static char vdev_name[256];
-	char *vdev_type = NULL;
 	uint64_t vdev_id = 0;
 
-	if (nvlist_lookup_string(nvroot, ZPOOL_CONFIG_TYPE,
-	    &vdev_type) != 0) {
-		vdev_type = "unknown";
-	}
+	char *vdev_type = (char *)"unknown";
+	nvlist_lookup_string(nvroot, ZPOOL_CONFIG_TYPE, &vdev_type);
+
 	if (nvlist_lookup_uint64(
-	    nvroot, ZPOOL_CONFIG_ID, &vdev_id) != 0) {
+	    nvroot, ZPOOL_CONFIG_ID, &vdev_id) != 0)
 		vdev_id = UINT64_MAX;
-	}
+
 	if (parent_name == NULL) {
 		(void) snprintf(vdev_name, sizeof (vdev_name), "%s",
 		    vdev_type);
@@ -298,22 +296,15 @@ static char *
 get_vdev_desc(nvlist_t *nvroot, const char *parent_name)
 {
 	static char vdev_desc[2 * MAXPATHLEN];
-	char *vdev_type = NULL;
-	uint64_t vdev_id = 0;
 	char vdev_value[MAXPATHLEN];
-	char *vdev_path = NULL;
 	char *s, *t;
 
-	if (nvlist_lookup_string(nvroot, ZPOOL_CONFIG_TYPE, &vdev_type) != 0) {
-		vdev_type = "unknown";
-	}
-	if (nvlist_lookup_uint64(nvroot, ZPOOL_CONFIG_ID, &vdev_id) != 0) {
-		vdev_id = UINT64_MAX;
-	}
-	if (nvlist_lookup_string(
-	    nvroot, ZPOOL_CONFIG_PATH, &vdev_path) != 0) {
-		vdev_path = NULL;
-	}
+	char *vdev_type = (char *)"unknown";
+	uint64_t vdev_id = UINT64_MAX;
+	char *vdev_path = NULL;
+	nvlist_lookup_string(nvroot, ZPOOL_CONFIG_TYPE, &vdev_type);
+	nvlist_lookup_uint64(nvroot, ZPOOL_CONFIG_ID, &vdev_id);
+	nvlist_lookup_string(nvroot, ZPOOL_CONFIG_PATH, &vdev_path);
 
 	if (parent_name == NULL) {
 		s = escape_string(vdev_type);
@@ -393,8 +384,8 @@ print_vdev_latency_stats(nvlist_t *nvroot, const char *pool_name,
 
 	/* short_names become part of the metric name and are influxdb-ready */
 	struct lat_lookup {
-	    char *name;
-	    char *short_name;
+	    const char *name;
+	    const char *short_name;
 	    uint64_t sum;
 	    uint64_t *array;
 	};
@@ -487,8 +478,8 @@ print_vdev_size_stats(nvlist_t *nvroot, const char *pool_name,
 
 	/* short_names become the field name */
 	struct size_lookup {
-	    char *name;
-	    char *short_name;
+	    const char *name;
+	    const char *short_name;
 	    uint64_t sum;
 	    uint64_t *array;
 	};
@@ -579,8 +570,8 @@ print_queue_stats(nvlist_t *nvroot, const char *pool_name,
 
 	/* short_names are used for the field name */
 	struct queue_lookup {
-	    char *name;
-	    char *short_name;
+	    const char *name;
+	    const char *short_name;
 	};
 	struct queue_lookup queue_type[] = {
 	    {ZPOOL_CONFIG_VDEV_SYNC_R_ACTIVE_QUEUE,	"sync_r_active"},
@@ -632,8 +623,8 @@ print_top_level_vdev_stats(nvlist_t *nvroot, const char *pool_name)
 
 	/* short_names become part of the metric name */
 	struct queue_lookup {
-	    char *name;
-	    char *short_name;
+	    const char *name;
+	    const char *short_name;
 	};
 	struct queue_lookup queue_type[] = {
 	    {ZPOOL_CONFIG_VDEV_SYNC_R_ACTIVE_QUEUE, "sync_r_active_queue"},
@@ -789,7 +780,7 @@ main(int argc, char *argv[])
 {
 	int opt;
 	int ret = 8;
-	char *line = NULL;
+	char *line = NULL, *ttags = NULL;
 	size_t len, tagslen = 0;
 	struct option long_options[] = {
 	    {"execd", no_argument, NULL, 'e'},
@@ -817,15 +808,17 @@ main(int argc, char *argv[])
 			sum_histogram_buckets = 1;
 			break;
 		case 't':
+			free(ttags);
 			tagslen = strlen(optarg) + 2;
-			tags = calloc(1, tagslen);
-			if (tags == NULL) {
+			ttags = calloc(1, tagslen);
+			if (ttags == NULL) {
 				fprintf(stderr,
 				    "error: cannot allocate memory "
 				    "for tags\n");
 				exit(1);
 			}
-			(void) snprintf(tags, tagslen, ",%s", optarg);
+			(void) snprintf(ttags, tagslen, ",%s", optarg);
+			tags = ttags;
 			break;
 		default:
 			usage(argv[0]);
diff --git a/cmd/ztest.c b/cmd/ztest.c
index 95f6107ff..ff425973a 100644
--- a/cmd/ztest.c
+++ b/cmd/ztest.c
@@ -264,7 +264,7 @@ extern unsigned long zfs_reconstruct_indirect_damage_fraction;
 
 static ztest_shared_opts_t *ztest_shared_opts;
 static ztest_shared_opts_t ztest_opts;
-static char *ztest_wkeydata = "abcdefghijklmnopqrstuvwxyz012345";
+static const char *const ztest_wkeydata = "abcdefghijklmnopqrstuvwxyz012345";
 
 typedef struct ztest_shared_ds {
 	uint64_t	zd_seq;
@@ -623,10 +623,10 @@ static void sig_handler(int signo)
 
 #define	FATAL_MSG_SZ	1024
 
-char *fatal_msg;
+static const char *fatal_msg;
 
 static __attribute__((format(printf, 2, 3))) __attribute__((noreturn)) void
-fatal(int do_perror, char *message, ...)
+fatal(int do_perror, const char *message, ...)
 {
 	va_list args;
 	int save_errno = errno;
@@ -724,7 +724,7 @@ typedef struct ztest_option {
 	const char	*long_opt_param;
 	const char	*comment;
 	unsigned int	default_int;
-	char		*default_str;
+	const char	*default_str;
 } ztest_option_t;
 
 /*
@@ -1200,30 +1200,31 @@ ztest_is_draid_spare(const char *name)
 }
 
 static nvlist_t *
-make_vdev_file(char *path, char *aux, char *pool, size_t size, uint64_t ashift)
+make_vdev_file(const char *path, const char *aux, const char *pool,
+    size_t size, uint64_t ashift)
 {
-	char *pathbuf;
+	char *pathbuf = NULL;
 	uint64_t vdev;
 	nvlist_t *file;
 	boolean_t draid_spare = B_FALSE;
 
-	pathbuf = umem_alloc(MAXPATHLEN, UMEM_NOFAIL);
 
 	if (ashift == 0)
 		ashift = ztest_get_ashift();
 
 	if (path == NULL) {
+		pathbuf = umem_alloc(MAXPATHLEN, UMEM_NOFAIL);
 		path = pathbuf;
 
 		if (aux != NULL) {
 			vdev = ztest_shared->zs_vdev_aux;
-			(void) snprintf(path, MAXPATHLEN,
+			(void) snprintf(pathbuf, MAXPATHLEN,
 			    ztest_aux_template, ztest_opts.zo_dir,
 			    pool == NULL ? ztest_opts.zo_pool : pool,
 			    aux, vdev);
 		} else {
 			vdev = ztest_shared->zs_vdev_next_leaf++;
-			(void) snprintf(path, MAXPATHLEN,
+			(void) snprintf(pathbuf, MAXPATHLEN,
 			    ztest_dev_template, ztest_opts.zo_dir,
 			    pool == NULL ? ztest_opts.zo_pool : pool, vdev);
 		}
@@ -1251,7 +1252,7 @@ make_vdev_file(char *path, char *aux, char *pool, size_t size, uint64_t ashift)
 }
 
 static nvlist_t *
-make_vdev_raid(char *path, char *aux, char *pool, size_t size,
+make_vdev_raid(const char *path, const char *aux, const char *pool, size_t size,
     uint64_t ashift, int r)
 {
 	nvlist_t *raid, **child;
@@ -1302,8 +1303,8 @@ make_vdev_raid(char *path, char *aux, char *pool, size_t size,
 }
 
 static nvlist_t *
-make_vdev_mirror(char *path, char *aux, char *pool, size_t size,
-    uint64_t ashift, int r, int m)
+make_vdev_mirror(const char *path, const char *aux, const char *pool,
+    size_t size, uint64_t ashift, int r, int m)
 {
 	nvlist_t *mirror, **child;
 	int c;
@@ -1330,8 +1331,8 @@ make_vdev_mirror(char *path, char *aux, char *pool, size_t size,
 }
 
 static nvlist_t *
-make_vdev_root(char *path, char *aux, char *pool, size_t size, uint64_t ashift,
-    const char *class, int r, int m, int t)
+make_vdev_root(const char *path, const char *aux, const char *pool, size_t size,
+    uint64_t ashift, const char *class, int r, int m, int t)
 {
 	nvlist_t *root, **child;
 	int c;
@@ -3371,7 +3372,7 @@ ztest_vdev_aux_add_remove(ztest_ds_t *zd, uint64_t id)
 	spa_t *spa = ztest_spa;
 	vdev_t *rvd = spa->spa_root_vdev;
 	spa_aux_vdev_t *sav;
-	char *aux;
+	const char *aux;
 	char *path;
 	uint64_t guid = 0;
 	int error, ignore_err = 0;
@@ -5271,7 +5272,7 @@ ztest_zap(ztest_ds_t *zd, uint64_t id)
 	dmu_tx_t *tx;
 	char propname[100], txgname[100];
 	int error;
-	char *hc[2] = { "s.acl.h", ".s.open.h.hyLZlg" };
+	const char *const hc[2] = { "s.acl.h", ".s.open.h.hyLZlg" };
 
 	od = umem_alloc(sizeof (ztest_od_t), UMEM_NOFAIL);
 	ztest_od_init(od, id, FTAG, 0, DMU_OT_ZAP_OTHER, 0, 0, 0);
@@ -6636,11 +6637,8 @@ ztest_global_vars_to_zdb_args(void)
 	char **args = calloc(2*ztest_opts.zo_gvars_count + 1, sizeof (char *));
 	char **cur = args;
 	for (size_t i = 0; i < ztest_opts.zo_gvars_count; i++) {
-		char *kv = ztest_opts.zo_gvars[i];
-		*cur = "-o";
-		cur++;
-		*cur = strdup(kv);
-		cur++;
+		*cur++ = (char *)"-o";
+		*cur++ = ztest_opts.zo_gvars[i];
 	}
 	ASSERT3P(cur, ==, &args[2*ztest_opts.zo_gvars_count]);
 	*cur = NULL;
@@ -6891,7 +6889,7 @@ ztest_trim(ztest_ds_t *zd, uint64_t id)
  * Verify pool integrity by running zdb.
  */
 static void
-ztest_run_zdb(char *pool)
+ztest_run_zdb(const char *pool)
 {
 	int status;
 	char *bin;
@@ -6949,12 +6947,12 @@ out:
 }
 
 static void
-ztest_walk_pool_directory(char *header)
+ztest_walk_pool_directory(const char *header)
 {
 	spa_t *spa = NULL;
 
 	if (ztest_opts.zo_verbose >= 6)
-		(void) printf("%s\n", header);
+		(void) puts(header);
 
 	mutex_enter(&spa_namespace_lock);
 	while ((spa = spa_next(spa)) != NULL)
@@ -7206,7 +7204,7 @@ ztest_thread(void *arg)
 }
 
 static void
-ztest_dataset_name(char *dsname, char *pool, int d)
+ztest_dataset_name(char *dsname, const char *pool, int d)
 {
 	(void) snprintf(dsname, ZFS_MAX_DATASET_NAME_LEN, "%s/ds_%d", pool, d);
 }
diff --git a/config/Rules.am b/config/Rules.am
index 07e72d33f..7162b7718 100644
--- a/config/Rules.am
+++ b/config/Rules.am
@@ -14,7 +14,7 @@ AM_CPPFLAGS = \
 
 AM_LIBTOOLFLAGS = --silent
 
-AM_CFLAGS  = -std=gnu99 -Wall -Wextra -Wstrict-prototypes -Wmissing-prototypes -Wno-sign-compare -Wno-missing-field-initializers
+AM_CFLAGS  = -std=gnu99 -Wall -Wextra -Wstrict-prototypes -Wmissing-prototypes -Wwrite-strings -Wno-sign-compare -Wno-missing-field-initializers
 AM_CFLAGS += -fno-strict-aliasing
 AM_CFLAGS += $(NO_OMIT_FRAME_POINTER)
 AM_CFLAGS += $(IMPLICIT_FALLTHROUGH)
diff --git a/etc/systemd/system-generators/zfs-mount-generator.c b/etc/systemd/system-generators/zfs-mount-generator.c
index f4c6c26a0..b07574e72 100644
--- a/etc/systemd/system-generators/zfs-mount-generator.c
+++ b/etc/systemd/system-generators/zfs-mount-generator.c
@@ -681,25 +681,28 @@ line_worker(char *line, const char *cachefile)
 	}
 	*(tofree++) = linktgt;
 
-	char *dependencies[][2] = {
+	struct dep {
+		const char *type;
+		char *list;
+	} deps[] = {
 		{"wants", wantedby},
 		{"requires", requiredby},
 		{}
 	};
-	for (__typeof__(&*dependencies) dep = &*dependencies; **dep; ++dep) {
-		if (!(*dep)[1])
+	for (struct dep *dep = deps; dep->type; ++dep) {
+		if (!dep->list)
 			continue;
 
-		for (char *reqby = strtok_r((*dep)[1], " ", &toktmp);
+		for (char *reqby = strtok_r(dep->list, " ", &toktmp);
 		    reqby;
 		    reqby = strtok_r(NULL, " ", &toktmp)) {
 			char *depdir;
 			if (asprintf(
-			    &depdir, "%s.%s", reqby, (*dep)[0]) == -1) {
+			    &depdir, "%s.%s", reqby, dep->type) == -1) {
 				fprintf(stderr, PROGNAME "[%d]: %s: "
 				    "out of memory for dependent dir name "
 				    "\"%s.%s\"!\n",
-				    getpid(), dataset, reqby, (*dep)[0]);
+				    getpid(), dataset, reqby, dep->type);
 				continue;
 			}
 
diff --git a/include/libzfs.h b/include/libzfs.h
index fe420de4d..6b4ead818 100644
--- a/include/libzfs.h
+++ b/include/libzfs.h
@@ -423,9 +423,9 @@ typedef enum {
 	ZPOOL_STATUS_OK
 } zpool_status_t;
 
-_LIBZFS_H zpool_status_t zpool_get_status(zpool_handle_t *, char **,
+_LIBZFS_H zpool_status_t zpool_get_status(zpool_handle_t *, const char **,
     zpool_errata_t *);
-_LIBZFS_H zpool_status_t zpool_import_status(nvlist_t *, char **,
+_LIBZFS_H zpool_status_t zpool_import_status(nvlist_t *, const char **,
     zpool_errata_t *);
 
 /*
@@ -870,8 +870,9 @@ _LIBZFS_H int zfs_unmountall(zfs_handle_t *, int);
 _LIBZFS_H int zfs_mount_delegation_check(void);
 
 #if defined(__linux__) || defined(__APPLE__)
-_LIBZFS_H int zfs_parse_mount_options(char *mntopts, unsigned long *mntflags,
-    unsigned long *zfsflags, int sloppy, char *badopt, char *mtabopt);
+_LIBZFS_H int zfs_parse_mount_options(const char *mntopts,
+    unsigned long *mntflags, unsigned long *zfsflags, int sloppy, char *badopt,
+    char *mtabopt);
 _LIBZFS_H void zfs_adjust_mount_options(zfs_handle_t *zhp, const char *mntpoint,
     char *mntopts, char *mtabopt);
 #endif
@@ -910,7 +911,7 @@ _LIBZFS_H int libzfs_run_process_get_stdout_nopath(const char *, char *[],
 
 _LIBZFS_H void libzfs_free_str_array(char **, int);
 
-_LIBZFS_H int libzfs_envvar_is_set(char *);
+_LIBZFS_H boolean_t libzfs_envvar_is_set(const char *);
 
 /*
  * Utility functions for zfs version
diff --git a/include/libzutil.h b/include/libzutil.h
index d0d5632c0..a46059b12 100644
--- a/include/libzutil.h
+++ b/include/libzutil.h
@@ -155,9 +155,9 @@ struct zfs_cmd;
 #define	ANSI_RESET	"\033[0m"
 #define	ANSI_BOLD	"\033[1m"
 
-_LIBZUTIL_H void color_start(char *color);
+_LIBZUTIL_H void color_start(const char *color);
 _LIBZUTIL_H void color_end(void);
-_LIBZUTIL_H int printf_color(char *color, char *format, ...);
+_LIBZUTIL_H int printf_color(const char *color, const char *format, ...);
 
 _LIBZUTIL_H const char *zfs_basename(const char *path);
 _LIBZUTIL_H ssize_t zfs_dirnamelen(const char *path);
diff --git a/include/os/freebsd/spl/sys/kmem.h b/include/os/freebsd/spl/sys/kmem.h
index dc3b4f5d7..a81cb1fb5 100644
--- a/include/os/freebsd/spl/sys/kmem.h
+++ b/include/os/freebsd/spl/sys/kmem.h
@@ -73,7 +73,7 @@ extern uint64_t spl_kmem_cache_entry_size(kmem_cache_t *cache);
 void *zfs_kmem_alloc(size_t size, int kmflags);
 void zfs_kmem_free(void *buf, size_t size);
 uint64_t kmem_size(void);
-kmem_cache_t *kmem_cache_create(char *name, size_t bufsize, size_t align,
+kmem_cache_t *kmem_cache_create(const char *name, size_t bufsize, size_t align,
     int (*constructor)(void *, void *, int), void (*destructor)(void *, void *),
     void (*reclaim)(void *) __unused, void *private, vmem_t *vmp, int cflags);
 void kmem_cache_destroy(kmem_cache_t *cache);
diff --git a/include/os/linux/spl/sys/kmem_cache.h b/include/os/linux/spl/sys/kmem_cache.h
index 48006ec5d..bd0ad5052 100644
--- a/include/os/linux/spl/sys/kmem_cache.h
+++ b/include/os/linux/spl/sys/kmem_cache.h
@@ -183,7 +183,7 @@ typedef struct spl_kmem_cache {
 } spl_kmem_cache_t;
 #define	kmem_cache_t		spl_kmem_cache_t
 
-extern spl_kmem_cache_t *spl_kmem_cache_create(char *name, size_t size,
+extern spl_kmem_cache_t *spl_kmem_cache_create(const char *name, size_t size,
     size_t align, spl_kmem_ctor_t ctor, spl_kmem_dtor_t dtor,
     void *reclaim, void *priv, void *vmp, int flags);
 extern void spl_kmem_cache_set_move(spl_kmem_cache_t *,
diff --git a/include/sys/arc.h b/include/sys/arc.h
index 4f9bfe48d..90b99c6cb 100644
--- a/include/sys/arc.h
+++ b/include/sys/arc.h
@@ -264,12 +264,12 @@ int arc_untransform(arc_buf_t *buf, spa_t *spa, const zbookmark_phys_t *zb,
 void arc_convert_to_raw(arc_buf_t *buf, uint64_t dsobj, boolean_t byteorder,
     dmu_object_type_t ot, const uint8_t *salt, const uint8_t *iv,
     const uint8_t *mac);
-arc_buf_t *arc_alloc_buf(spa_t *spa, void *tag, arc_buf_contents_t type,
+arc_buf_t *arc_alloc_buf(spa_t *spa, const void *tag, arc_buf_contents_t type,
     int32_t size);
-arc_buf_t *arc_alloc_compressed_buf(spa_t *spa, void *tag,
+arc_buf_t *arc_alloc_compressed_buf(spa_t *spa, const void *tag,
     uint64_t psize, uint64_t lsize, enum zio_compress compression_type,
     uint8_t complevel);
-arc_buf_t *arc_alloc_raw_buf(spa_t *spa, void *tag, uint64_t dsobj,
+arc_buf_t *arc_alloc_raw_buf(spa_t *spa, const void *tag, uint64_t dsobj,
     boolean_t byteorder, const uint8_t *salt, const uint8_t *iv,
     const uint8_t *mac, dmu_object_type_t ot, uint64_t psize, uint64_t lsize,
     enum zio_compress compression_type, uint8_t complevel);
diff --git a/include/sys/dbuf.h b/include/sys/dbuf.h
index 60f8d5d74..959e111ce 100644
--- a/include/sys/dbuf.h
+++ b/include/sys/dbuf.h
@@ -339,12 +339,12 @@ int dbuf_spill_set_blksz(dmu_buf_t *db, uint64_t blksz, dmu_tx_t *tx);
 
 void dbuf_rm_spill(struct dnode *dn, dmu_tx_t *tx);
 
-dmu_buf_impl_t *dbuf_hold(struct dnode *dn, uint64_t blkid, void *tag);
+dmu_buf_impl_t *dbuf_hold(struct dnode *dn, uint64_t blkid, const void *tag);
 dmu_buf_impl_t *dbuf_hold_level(struct dnode *dn, int level, uint64_t blkid,
-    void *tag);
+    const void *tag);
 int dbuf_hold_impl(struct dnode *dn, uint8_t level, uint64_t blkid,
     boolean_t fail_sparse, boolean_t fail_uncached,
-    void *tag, dmu_buf_impl_t **dbp);
+    const void *tag, dmu_buf_impl_t **dbp);
 
 int dbuf_prefetch_impl(struct dnode *dn, int64_t level, uint64_t blkid,
     zio_priority_t prio, arc_flags_t aflags, dbuf_prefetch_fn cb,
@@ -352,13 +352,14 @@ int dbuf_prefetch_impl(struct dnode *dn, int64_t level, uint64_t blkid,
 int dbuf_prefetch(struct dnode *dn, int64_t level, uint64_t blkid,
     zio_priority_t prio, arc_flags_t aflags);
 
-void dbuf_add_ref(dmu_buf_impl_t *db, void *tag);
+void dbuf_add_ref(dmu_buf_impl_t *db, const void *tag);
 boolean_t dbuf_try_add_ref(dmu_buf_t *db, objset_t *os, uint64_t obj,
-    uint64_t blkid, void *tag);
+    uint64_t blkid, const void *tag);
 uint64_t dbuf_refcount(dmu_buf_impl_t *db);
 
-void dbuf_rele(dmu_buf_impl_t *db, void *tag);
-void dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag, boolean_t evicting);
+void dbuf_rele(dmu_buf_impl_t *db, const void *tag);
+void dbuf_rele_and_unlock(dmu_buf_impl_t *db, const void *tag,
+    boolean_t evicting);
 
 dmu_buf_impl_t *dbuf_find(struct objset *os, uint64_t object, uint8_t level,
     uint64_t blkid);
@@ -385,8 +386,10 @@ void dbuf_destroy(dmu_buf_impl_t *db);
 void dbuf_unoverride(dbuf_dirty_record_t *dr);
 void dbuf_sync_list(list_t *list, int level, dmu_tx_t *tx);
 void dbuf_release_bp(dmu_buf_impl_t *db);
-db_lock_type_t dmu_buf_lock_parent(dmu_buf_impl_t *db, krw_t rw, void *tag);
-void dmu_buf_unlock_parent(dmu_buf_impl_t *db, db_lock_type_t type, void *tag);
+db_lock_type_t dmu_buf_lock_parent(dmu_buf_impl_t *db, krw_t rw,
+    const void *tag);
+void dmu_buf_unlock_parent(dmu_buf_impl_t *db, db_lock_type_t type,
+    const void *tag);
 
 void dbuf_free_range(struct dnode *dn, uint64_t start, uint64_t end,
     struct dmu_tx *);
diff --git a/include/sys/dmu.h b/include/sys/dmu.h
index 03513f9f2..6bd7a3e9a 100644
--- a/include/sys/dmu.h
+++ b/include/sys/dmu.h
@@ -319,11 +319,12 @@ void zfs_znode_byteswap(void *buf, size_t size);
 typedef void dmu_objset_create_sync_func_t(objset_t *os, void *arg,
     cred_t *cr, dmu_tx_t *tx);
 
-int dmu_objset_hold(const char *name, void *tag, objset_t **osp);
+int dmu_objset_hold(const char *name, const void *tag, objset_t **osp);
 int dmu_objset_own(const char *name, dmu_objset_type_t type,
-    boolean_t readonly, boolean_t key_required, void *tag, objset_t **osp);
-void dmu_objset_rele(objset_t *os, void *tag);
-void dmu_objset_disown(objset_t *os, boolean_t key_required, void *tag);
+    boolean_t readonly, boolean_t key_required, const void *tag,
+    objset_t **osp);
+void dmu_objset_rele(objset_t *os, const void *tag);
+void dmu_objset_disown(objset_t *os, boolean_t key_required, const void *tag);
 int dmu_objset_open_ds(struct dsl_dataset *ds, objset_t **osp);
 
 void dmu_objset_evict_dbufs(objset_t *os);
@@ -407,7 +408,7 @@ uint64_t dmu_object_alloc_dnsize(objset_t *os, dmu_object_type_t ot,
     int dnodesize, dmu_tx_t *tx);
 uint64_t dmu_object_alloc_hold(objset_t *os, dmu_object_type_t ot,
     int blocksize, int indirect_blockshift, dmu_object_type_t bonustype,
-    int bonuslen, int dnodesize, dnode_t **allocated_dnode, void *tag,
+    int bonuslen, int dnodesize, dnode_t **allocated_dnode, const void *tag,
     dmu_tx_t *tx);
 int dmu_object_claim(objset_t *os, uint64_t object, dmu_object_type_t ot,
     int blocksize, dmu_object_type_t bonus_type, int bonus_len, dmu_tx_t *tx);
@@ -524,8 +525,9 @@ void dmu_write_policy(objset_t *os, dnode_t *dn, int level, int wp,
  *
  * Returns ENOENT, EIO, or 0.
  */
-int dmu_bonus_hold(objset_t *os, uint64_t object, void *tag, dmu_buf_t **dbp);
-int dmu_bonus_hold_by_dnode(dnode_t *dn, void *tag, dmu_buf_t **dbp,
+int dmu_bonus_hold(objset_t *os, uint64_t object, const void *tag,
+    dmu_buf_t **dbp);
+int dmu_bonus_hold_by_dnode(dnode_t *dn, const void *tag, dmu_buf_t **dbp,
     uint32_t flags);
 int dmu_bonus_max(void);
 int dmu_set_bonus(dmu_buf_t *, int, dmu_tx_t *);
@@ -537,11 +539,11 @@ int dmu_rm_spill(objset_t *, uint64_t, dmu_tx_t *);
  * Special spill buffer support used by "SA" framework
  */
 
-int dmu_spill_hold_by_bonus(dmu_buf_t *bonus, uint32_t flags, void *tag,
+int dmu_spill_hold_by_bonus(dmu_buf_t *bonus, uint32_t flags, const void *tag,
     dmu_buf_t **dbp);
 int dmu_spill_hold_by_dnode(dnode_t *dn, uint32_t flags,
-    void *tag, dmu_buf_t **dbp);
-int dmu_spill_hold_existing(dmu_buf_t *bonus, void *tag, dmu_buf_t **dbp);
+    const void *tag, dmu_buf_t **dbp);
+int dmu_spill_hold_existing(dmu_buf_t *bonus, const void *tag, dmu_buf_t **dbp);
 
 /*
  * Obtain the DMU buffer from the specified object which contains the
@@ -558,13 +560,14 @@ int dmu_spill_hold_existing(dmu_buf_t *bonus, void *tag, dmu_buf_t **dbp);
  * The object number must be a valid, allocated object number.
  */
 int dmu_buf_hold(objset_t *os, uint64_t object, uint64_t offset,
-    void *tag, dmu_buf_t **, int flags);
+    const void *tag, dmu_buf_t **, int flags);
 int dmu_buf_hold_array(objset_t *os, uint64_t object, uint64_t offset,
-    uint64_t length, int read, void *tag, int *numbufsp, dmu_buf_t ***dbpp);
+    uint64_t length, int read, const void *tag, int *numbufsp,
+    dmu_buf_t ***dbpp);
 int dmu_buf_hold_by_dnode(dnode_t *dn, uint64_t offset,
-    void *tag, dmu_buf_t **dbp, int flags);
+    const void *tag, dmu_buf_t **dbp, int flags);
 int dmu_buf_hold_array_by_dnode(dnode_t *dn, uint64_t offset,
-    uint64_t length, boolean_t read, void *tag, int *numbufsp,
+    uint64_t length, boolean_t read, const void *tag, int *numbufsp,
     dmu_buf_t ***dbpp, uint32_t flags);
 /*
  * Add a reference to a dmu buffer that has already been held via
@@ -580,9 +583,9 @@ void dmu_buf_add_ref(dmu_buf_t *db, void* tag);
  * one hold by a user other than the syncer.
  */
 boolean_t dmu_buf_try_add_ref(dmu_buf_t *, objset_t *os, uint64_t object,
-    uint64_t blkid, void *tag);
+    uint64_t blkid, const void *tag);
 
-void dmu_buf_rele(dmu_buf_t *db, void *tag);
+void dmu_buf_rele(dmu_buf_t *db, const void *tag);
 uint64_t dmu_buf_refcount(dmu_buf_t *db);
 uint64_t dmu_buf_user_refcount(dmu_buf_t *db);
 
@@ -597,9 +600,9 @@ uint64_t dmu_buf_user_refcount(dmu_buf_t *db);
  * individually with dmu_buf_rele.
  */
 int dmu_buf_hold_array_by_bonus(dmu_buf_t *db, uint64_t offset,
-    uint64_t length, boolean_t read, void *tag,
+    uint64_t length, boolean_t read, const void *tag,
     int *numbufsp, dmu_buf_t ***dbpp);
-void dmu_buf_rele_array(dmu_buf_t **, int numbufs, void *tag);
+void dmu_buf_rele_array(dmu_buf_t **, int numbufs, const void *tag);
 
 typedef void dmu_buf_evict_func_t(void *user_ptr);
 
@@ -895,12 +898,12 @@ typedef struct dmu_object_type_info {
 	boolean_t		ot_metadata;
 	boolean_t		ot_dbuf_metadata_cache;
 	boolean_t		ot_encrypt;
-	char			*ot_name;
+	const char		*ot_name;
 } dmu_object_type_info_t;
 
 typedef const struct dmu_object_byteswap_info {
 	arc_byteswap_func_t	 ob_func;
-	char			*ob_name;
+	const char		*ob_name;
 } dmu_object_byteswap_info_t;
 
 extern const dmu_object_type_info_t dmu_ot[DMU_OT_NUMTYPES];
diff --git a/include/sys/dmu_impl.h b/include/sys/dmu_impl.h
index def4aadba..95ec11ce2 100644
--- a/include/sys/dmu_impl.h
+++ b/include/sys/dmu_impl.h
@@ -248,7 +248,7 @@ typedef struct dmu_sendstatus {
 void dmu_object_zapify(objset_t *, uint64_t, dmu_object_type_t, dmu_tx_t *);
 void dmu_object_free_zapified(objset_t *, uint64_t, dmu_tx_t *);
 int dmu_buf_hold_noread(objset_t *, uint64_t, uint64_t,
-    void *, dmu_buf_t **);
+    const void *, dmu_buf_t **);
 
 #ifdef	__cplusplus
 }
diff --git a/include/sys/dmu_objset.h b/include/sys/dmu_objset.h
index 7ade2dc91..782338fd2 100644
--- a/include/sys/dmu_objset.h
+++ b/include/sys/dmu_objset.h
@@ -201,19 +201,19 @@ struct objset {
 #define	DMU_PROJECTUSED_DNODE(os) ((os)->os_projectused_dnode.dnh_dnode)
 
 /* called from zpl */
-int dmu_objset_hold(const char *name, void *tag, objset_t **osp);
-int dmu_objset_hold_flags(const char *name, boolean_t decrypt, void *tag,
+int dmu_objset_hold(const char *name, const void *tag, objset_t **osp);
+int dmu_objset_hold_flags(const char *name, boolean_t decrypt, const void *tag,
     objset_t **osp);
 int dmu_objset_own(const char *name, dmu_objset_type_t type,
-    boolean_t readonly, boolean_t decrypt, void *tag, objset_t **osp);
+    boolean_t readonly, boolean_t decrypt, const void *tag, objset_t **osp);
 int dmu_objset_own_obj(struct dsl_pool *dp, uint64_t obj,
     dmu_objset_type_t type, boolean_t readonly, boolean_t decrypt,
-    void *tag, objset_t **osp);
+    const void *tag, objset_t **osp);
 void dmu_objset_refresh_ownership(struct dsl_dataset *ds,
-    struct dsl_dataset **newds, boolean_t decrypt, void *tag);
-void dmu_objset_rele(objset_t *os, void *tag);
-void dmu_objset_rele_flags(objset_t *os, boolean_t decrypt, void *tag);
-void dmu_objset_disown(objset_t *os, boolean_t decrypt, void *tag);
+    struct dsl_dataset **newds, boolean_t decrypt, const void *tag);
+void dmu_objset_rele(objset_t *os, const void *tag);
+void dmu_objset_rele_flags(objset_t *os, boolean_t decrypt, const void *tag);
+void dmu_objset_disown(objset_t *os, boolean_t decrypt, const void *tag);
 int dmu_objset_from_ds(struct dsl_dataset *ds, objset_t **osp);
 
 void dmu_objset_stats(objset_t *os, nvlist_t *nv);
diff --git a/include/sys/dnode.h b/include/sys/dnode.h
index 33d9389d5..9745ae5bb 100644
--- a/include/sys/dnode.h
+++ b/include/sys/dnode.h
@@ -334,7 +334,7 @@ struct dnode {
 	kcondvar_t dn_notxholds;
 	kcondvar_t dn_nodnholds;
 	enum dnode_dirtycontext dn_dirtyctx;
-	void *dn_dirtyctx_firstset;		/* dbg: contents meaningless */
+	const void *dn_dirtyctx_firstset;	/* dbg: contents meaningless */
 
 	/* protected by own devices */
 	zfs_refcount_t dn_tx_holds;
@@ -418,16 +418,16 @@ void dnode_setbonus_type(dnode_t *dn, dmu_object_type_t, dmu_tx_t *tx);
 void dnode_rm_spill(dnode_t *dn, dmu_tx_t *tx);
 
 int dnode_hold(struct objset *dd, uint64_t object,
-    void *ref, dnode_t **dnp);
+    const void *ref, dnode_t **dnp);
 int dnode_hold_impl(struct objset *dd, uint64_t object, int flag, int dn_slots,
-    void *ref, dnode_t **dnp);
-boolean_t dnode_add_ref(dnode_t *dn, void *ref);
-void dnode_rele(dnode_t *dn, void *ref);
-void dnode_rele_and_unlock(dnode_t *dn, void *tag, boolean_t evicting);
+    const void *ref, dnode_t **dnp);
+boolean_t dnode_add_ref(dnode_t *dn, const void *ref);
+void dnode_rele(dnode_t *dn, const void *ref);
+void dnode_rele_and_unlock(dnode_t *dn, const void *tag, boolean_t evicting);
 int dnode_try_claim(objset_t *os, uint64_t object, int slots);
 boolean_t dnode_is_dirty(dnode_t *dn);
 void dnode_setdirty(dnode_t *dn, dmu_tx_t *tx);
-void dnode_set_dirtyctx(dnode_t *dn, dmu_tx_t *tx, void *tag);
+void dnode_set_dirtyctx(dnode_t *dn, dmu_tx_t *tx, const void *tag);
 void dnode_sync(dnode_t *dn, dmu_tx_t *tx);
 void dnode_allocate(dnode_t *dn, dmu_object_type_t ot, int blocksize, int ibs,
     dmu_object_type_t bonustype, int bonuslen, int dn_slots, dmu_tx_t *tx);
diff --git a/include/sys/dsl_dataset.h b/include/sys/dsl_dataset.h
index 561d49dac..25f86bce2 100644
--- a/include/sys/dsl_dataset.h
+++ b/include/sys/dsl_dataset.h
@@ -220,7 +220,7 @@ typedef struct dsl_dataset {
 	kmutex_t ds_lock;
 	objset_t *ds_objset;
 	uint64_t ds_userrefs;
-	void *ds_owner;
+	const void *ds_owner;
 
 	/*
 	 * Long holds prevent the ds from being destroyed; they allow the
@@ -319,32 +319,34 @@ typedef enum ds_hold_flags {
 	DS_HOLD_FLAG_DECRYPT	= 1 << 0 /* needs access to encrypted data */
 } ds_hold_flags_t;
 
-int dsl_dataset_hold(struct dsl_pool *dp, const char *name, void *tag,
+int dsl_dataset_hold(struct dsl_pool *dp, const char *name, const void *tag,
     dsl_dataset_t **dsp);
 int dsl_dataset_hold_flags(struct dsl_pool *dp, const char *name,
-    ds_hold_flags_t flags, void *tag, dsl_dataset_t **dsp);
+    ds_hold_flags_t flags, const void *tag, dsl_dataset_t **dsp);
 boolean_t dsl_dataset_try_add_ref(struct dsl_pool *dp, dsl_dataset_t *ds,
-    void *tag);
+    const void *tag);
 int dsl_dataset_create_key_mapping(dsl_dataset_t *ds);
 int dsl_dataset_hold_obj_flags(struct dsl_pool *dp, uint64_t dsobj,
-    ds_hold_flags_t flags, void *tag, dsl_dataset_t **);
+    ds_hold_flags_t flags, const void *tag, dsl_dataset_t **);
 void dsl_dataset_remove_key_mapping(dsl_dataset_t *ds);
 int dsl_dataset_hold_obj(struct dsl_pool *dp, uint64_t dsobj,
-    void *tag, dsl_dataset_t **);
+    const void *tag, dsl_dataset_t **);
 void dsl_dataset_rele_flags(dsl_dataset_t *ds, ds_hold_flags_t flags,
-    void *tag);
-void dsl_dataset_rele(dsl_dataset_t *ds, void *tag);
+    const void *tag);
+void dsl_dataset_rele(dsl_dataset_t *ds, const void *tag);
 int dsl_dataset_own(struct dsl_pool *dp, const char *name,
-    ds_hold_flags_t flags, void *tag, dsl_dataset_t **dsp);
+    ds_hold_flags_t flags, const void *tag, dsl_dataset_t **dsp);
 int dsl_dataset_own_force(struct dsl_pool *dp, const char *name,
-    ds_hold_flags_t flags, void *tag, dsl_dataset_t **dsp);
+    ds_hold_flags_t flags, const void *tag, dsl_dataset_t **dsp);
 int dsl_dataset_own_obj(struct dsl_pool *dp, uint64_t dsobj,
-    ds_hold_flags_t flags, void *tag, dsl_dataset_t **dsp);
+    ds_hold_flags_t flags, const void *tag, dsl_dataset_t **dsp);
 int dsl_dataset_own_obj_force(struct dsl_pool *dp, uint64_t dsobj,
-    ds_hold_flags_t flags, void *tag, dsl_dataset_t **dsp);
-void dsl_dataset_disown(dsl_dataset_t *ds, ds_hold_flags_t flags, void *tag);
+    ds_hold_flags_t flags, const void *tag, dsl_dataset_t **dsp);
+void dsl_dataset_disown(dsl_dataset_t *ds, ds_hold_flags_t flags,
+    const void *tag);
 void dsl_dataset_name(dsl_dataset_t *ds, char *name);
-boolean_t dsl_dataset_tryown(dsl_dataset_t *ds, void *tag, boolean_t override);
+boolean_t dsl_dataset_tryown(dsl_dataset_t *ds, const void *tag,
+    boolean_t override);
 int dsl_dataset_namelen(dsl_dataset_t *ds);
 boolean_t dsl_dataset_has_owner(dsl_dataset_t *ds);
 uint64_t dsl_dataset_create_sync(dsl_dir_t *pds, const char *lastname,
diff --git a/include/sys/dsl_pool.h b/include/sys/dsl_pool.h
index 15e0efc3e..5bb5ef20d 100644
--- a/include/sys/dsl_pool.h
+++ b/include/sys/dsl_pool.h
@@ -177,9 +177,9 @@ void dsl_pool_mos_diduse_space(dsl_pool_t *dp,
 void dsl_pool_ckpoint_diduse_space(dsl_pool_t *dp,
     int64_t used, int64_t comp, int64_t uncomp);
 boolean_t dsl_pool_need_dirty_delay(dsl_pool_t *dp);
-void dsl_pool_config_enter(dsl_pool_t *dp, void *tag);
-void dsl_pool_config_enter_prio(dsl_pool_t *dp, void *tag);
-void dsl_pool_config_exit(dsl_pool_t *dp, void *tag);
+void dsl_pool_config_enter(dsl_pool_t *dp, const void *tag);
+void dsl_pool_config_enter_prio(dsl_pool_t *dp, const void *tag);
+void dsl_pool_config_exit(dsl_pool_t *dp, const void *tag);
 boolean_t dsl_pool_config_held(dsl_pool_t *dp);
 boolean_t dsl_pool_config_held_writer(dsl_pool_t *dp);
 
@@ -192,8 +192,8 @@ int dsl_pool_user_release(dsl_pool_t *dp, uint64_t dsobj,
     const char *tag, dmu_tx_t *tx);
 void dsl_pool_clean_tmp_userrefs(dsl_pool_t *dp);
 int dsl_pool_open_special_dir(dsl_pool_t *dp, const char *name, dsl_dir_t **);
-int dsl_pool_hold(const char *name, void *tag, dsl_pool_t **dp);
-void dsl_pool_rele(dsl_pool_t *dp, void *tag);
+int dsl_pool_hold(const char *name, const void *tag, dsl_pool_t **dp);
+void dsl_pool_rele(dsl_pool_t *dp, const void *tag);
 
 void dsl_pool_create_obsolete_bpobj(dsl_pool_t *dp, dmu_tx_t *tx);
 void dsl_pool_destroy_obsolete_bpobj(dsl_pool_t *dp, dmu_tx_t *tx);
diff --git a/include/sys/rrwlock.h b/include/sys/rrwlock.h
index 8d296ef28..51ac364af 100644
--- a/include/sys/rrwlock.h
+++ b/include/sys/rrwlock.h
@@ -72,11 +72,11 @@ typedef struct rrwlock {
  */
 void rrw_init(rrwlock_t *rrl, boolean_t track_all);
 void rrw_destroy(rrwlock_t *rrl);
-void rrw_enter(rrwlock_t *rrl, krw_t rw, void *tag);
-void rrw_enter_read(rrwlock_t *rrl, void *tag);
-void rrw_enter_read_prio(rrwlock_t *rrl, void *tag);
+void rrw_enter(rrwlock_t *rrl, krw_t rw, const void *tag);
+void rrw_enter_read(rrwlock_t *rrl, const void *tag);
+void rrw_enter_read_prio(rrwlock_t *rrl, const void *tag);
 void rrw_enter_write(rrwlock_t *rrl);
-void rrw_exit(rrwlock_t *rrl, void *tag);
+void rrw_exit(rrwlock_t *rrl, const void *tag);
 boolean_t rrw_held(rrwlock_t *rrl, krw_t rw);
 void rrw_tsd_destroy(void *arg);
 
@@ -99,10 +99,10 @@ typedef struct rrmlock {
 
 void rrm_init(rrmlock_t *rrl, boolean_t track_all);
 void rrm_destroy(rrmlock_t *rrl);
-void rrm_enter(rrmlock_t *rrl, krw_t rw, void *tag);
-void rrm_enter_read(rrmlock_t *rrl, void *tag);
+void rrm_enter(rrmlock_t *rrl, krw_t rw, const void *tag);
+void rrm_enter_read(rrmlock_t *rrl, const void *tag);
 void rrm_enter_write(rrmlock_t *rrl);
-void rrm_exit(rrmlock_t *rrl, void *tag);
+void rrm_exit(rrmlock_t *rrl, const void *tag);
 boolean_t rrm_held(rrmlock_t *rrl, krw_t rw);
 
 #define	RRM_READ_HELD(x)	rrm_held(x, RW_READER)
diff --git a/include/sys/sa.h b/include/sys/sa.h
index 32f6bd0cc..709018bde 100644
--- a/include/sys/sa.h
+++ b/include/sys/sa.h
@@ -49,7 +49,7 @@ typedef uint16_t	sa_attr_type_t;
  * Attribute to register support for.
  */
 typedef struct sa_attr_reg {
-	char 			*sa_name;	/* attribute name */
+	const char 		*sa_name;	/* attribute name */
 	uint16_t 		sa_length;
 	sa_bswap_type_t		sa_byteswap;	/* bswap function enum */
 	sa_attr_type_t 		sa_attr; /* filled in during registration */
diff --git a/include/sys/spa.h b/include/sys/spa.h
index 442bc7792..62fad3378 100644
--- a/include/sys/spa.h
+++ b/include/sys/spa.h
@@ -606,7 +606,7 @@ typedef struct blkptr {
 
 #define	SNPRINTF_BLKPTR(func, ws, buf, size, bp, type, checksum, compress) \
 {									\
-	static const char *copyname[] =					\
+	static const char *const copyname[] =				\
 	    { "zero", "single", "double", "triple" };			\
 	int len = 0;							\
 	int copies = 0;							\
@@ -743,8 +743,8 @@ typedef enum trim_type {
 } trim_type_t;
 
 /* state manipulation functions */
-extern int spa_open(const char *pool, spa_t **, void *tag);
-extern int spa_open_rewind(const char *pool, spa_t **, void *tag,
+extern int spa_open(const char *pool, spa_t **, const void *tag);
+extern int spa_open_rewind(const char *pool, spa_t **, const void *tag,
     nvlist_t *policy, nvlist_t **config);
 extern int spa_get_stats(const char *pool, nvlist_t **config, char *altroot,
     size_t buflen);
@@ -801,8 +801,8 @@ extern int spa_vdev_trim(spa_t *spa, nvlist_t *nv, uint64_t cmd_type,
     uint64_t rate, boolean_t partial, boolean_t secure, nvlist_t *vdev_errlist);
 extern int spa_vdev_setpath(spa_t *spa, uint64_t guid, const char *newpath);
 extern int spa_vdev_setfru(spa_t *spa, uint64_t guid, const char *newfru);
-extern int spa_vdev_split_mirror(spa_t *spa, char *newname, nvlist_t *config,
-    nvlist_t *props, boolean_t exp);
+extern int spa_vdev_split_mirror(spa_t *spa, const char *newname,
+    nvlist_t *config, nvlist_t *props, boolean_t exp);
 
 /* spare state (which is global across all pools) */
 extern void spa_spare_add(vdev_t *vd);
@@ -860,9 +860,9 @@ extern void spa_remove(spa_t *spa);
 extern spa_t *spa_next(spa_t *prev);
 
 /* Refcount functions */
-extern void spa_open_ref(spa_t *spa, void *tag);
-extern void spa_close(spa_t *spa, void *tag);
-extern void spa_async_close(spa_t *spa, void *tag);
+extern void spa_open_ref(spa_t *spa, const void *tag);
+extern void spa_close(spa_t *spa, const void *tag);
+extern void spa_async_close(spa_t *spa, const void *tag);
 extern boolean_t spa_refcount_zero(spa_t *spa);
 
 #define	SCL_NONE	0x00
@@ -971,7 +971,8 @@ extern int spa_import_progress_set_state(uint64_t pool_guid,
     spa_load_state_t spa_load_state);
 
 /* Pool configuration locks */
-extern int spa_config_tryenter(spa_t *spa, int locks, void *tag, krw_t rw);
+extern int spa_config_tryenter(spa_t *spa, int locks, const void *tag,
+    krw_t rw);
 extern void spa_config_enter(spa_t *spa, int locks, const void *tag, krw_t rw);
 extern void spa_config_exit(spa_t *spa, int locks, const void *tag);
 extern int spa_config_held(spa_t *spa, int locks, krw_t rw);
diff --git a/include/sys/zfs_fuid.h b/include/sys/zfs_fuid.h
index b5b37db29..1975e57cf 100644
--- a/include/sys/zfs_fuid.h
+++ b/include/sys/zfs_fuid.h
@@ -112,15 +112,13 @@ extern zfs_fuid_info_t *zfs_fuid_info_alloc(void);
 extern void zfs_fuid_info_free(zfs_fuid_info_t *);
 extern boolean_t zfs_groupmember(zfsvfs_t *, uint64_t, cred_t *);
 void zfs_fuid_sync(zfsvfs_t *, dmu_tx_t *);
-extern int zfs_fuid_find_by_domain(zfsvfs_t *, const char *domain,
-    char **retdomain, boolean_t addok);
 extern const char *zfs_fuid_find_by_idx(zfsvfs_t *zfsvfs, uint32_t idx);
 extern void zfs_fuid_txhold(zfsvfs_t *zfsvfs, dmu_tx_t *tx);
 extern int zfs_id_to_fuidstr(zfsvfs_t *zfsvfs, const char *domain, uid_t rid,
     char *buf, size_t len, boolean_t addok);
 #endif
 
-char *zfs_fuid_idx_domain(avl_tree_t *, uint32_t);
+const char *zfs_fuid_idx_domain(avl_tree_t *, uint32_t);
 void zfs_fuid_avl_tree_create(avl_tree_t *, avl_tree_t *);
 uint64_t zfs_fuid_table_load(objset_t *, uint64_t, avl_tree_t *, avl_tree_t *);
 void zfs_fuid_table_destroy(avl_tree_t *, avl_tree_t *);
diff --git a/include/sys/zio_checksum.h b/include/sys/zio_checksum.h
index a2ce50816..989f125e6 100644
--- a/include/sys/zio_checksum.h
+++ b/include/sys/zio_checksum.h
@@ -90,7 +90,7 @@ typedef const struct zio_checksum_info {
 	zio_checksum_tmpl_init_t	*ci_tmpl_init;
 	zio_checksum_tmpl_free_t	*ci_tmpl_free;
 	zio_checksum_flags_t		ci_flags;
-	char				*ci_name;	/* descriptive name */
+	const char			*ci_name;	/* descriptive name */
 } zio_checksum_info_t;
 
 typedef struct zio_bad_cksum {
@@ -102,7 +102,7 @@ typedef struct zio_bad_cksum {
 	uint8_t			zbc_has_cksum;	/* expected/actual valid */
 } zio_bad_cksum_t;
 
-_SYS_ZIO_CHECKSUM_H zio_checksum_info_t
+_SYS_ZIO_CHECKSUM_H const zio_checksum_info_t
     zio_checksum_table[ZIO_CHECKSUM_FUNCTIONS];
 
 /*
diff --git a/include/sys/zio_compress.h b/include/sys/zio_compress.h
index 4a22ad2a2..26600b43b 100644
--- a/include/sys/zio_compress.h
+++ b/include/sys/zio_compress.h
@@ -145,14 +145,14 @@ typedef int zio_decompress_abd_func_t(abd_t *src, void *dst,
  * Information about each compression function.
  */
 typedef const struct zio_compress_info {
-	char				*ci_name;
+	const char			*ci_name;
 	int				ci_level;
 	zio_compress_func_t		*ci_compress;
 	zio_decompress_func_t		*ci_decompress;
 	zio_decompresslevel_func_t	*ci_decompress_level;
 } zio_compress_info_t;
 
-extern zio_compress_info_t zio_compress_table[ZIO_COMPRESS_FUNCTIONS];
+extern const zio_compress_info_t zio_compress_table[ZIO_COMPRESS_FUNCTIONS];
 
 /*
  * lz4 compression init & free
diff --git a/include/sys/zio_crypt.h b/include/sys/zio_crypt.h
index f1edd76f0..6a3efabb0 100644
--- a/include/sys/zio_crypt.h
+++ b/include/sys/zio_crypt.h
@@ -67,7 +67,7 @@ typedef struct zio_crypt_info {
 	size_t ci_keylen;
 
 	/* human-readable name of the encryption algorithm */
-	char *ci_name;
+	const char *ci_name;
 } zio_crypt_info_t;
 
 extern const zio_crypt_info_t zio_crypt_table[ZIO_CRYPT_FUNCTIONS];
diff --git a/include/zfs_comutil.h b/include/zfs_comutil.h
index ea2da4a15..51625a5cd 100644
--- a/include/zfs_comutil.h
+++ b/include/zfs_comutil.h
@@ -34,7 +34,7 @@ extern "C" {
 #endif
 
 _ZFS_COMUTIL_H boolean_t zfs_allocatable_devs(nvlist_t *);
-_ZFS_COMUTIL_H boolean_t zfs_special_devs(nvlist_t *, char *);
+_ZFS_COMUTIL_H boolean_t zfs_special_devs(nvlist_t *, const char *);
 _ZFS_COMUTIL_H void zpool_get_load_policy(nvlist_t *, zpool_load_policy_t *);
 
 _ZFS_COMUTIL_H int zfs_zpl_version_map(int spa_version);
diff --git a/include/zfs_deleg.h b/include/zfs_deleg.h
index 77f64786b..760d16aef 100644
--- a/include/zfs_deleg.h
+++ b/include/zfs_deleg.h
@@ -81,7 +81,7 @@ typedef enum {
 } zfs_deleg_note_t;
 
 typedef struct zfs_deleg_perm_tab {
-	char *z_perm;
+	const char *z_perm;
 	zfs_deleg_note_t z_note;
 } zfs_deleg_perm_tab_t;
 
diff --git a/lib/libspl/include/os/linux/sys/mnttab.h b/lib/libspl/include/os/linux/sys/mnttab.h
index 1957293d5..21592aaaa 100644
--- a/lib/libspl/include/os/linux/sys/mnttab.h
+++ b/lib/libspl/include/os/linux/sys/mnttab.h
@@ -74,7 +74,7 @@ extern int getmntany(FILE *fp, struct mnttab *mp, struct mnttab *mpref);
 extern int _sol_getmntent(FILE *fp, struct mnttab *mp);
 extern int getextmntent(const char *path, struct extmnttab *mp,
     struct stat64 *statbuf);
-static inline char *_sol_hasmntopt(struct mnttab *mnt, char *opt)
+static inline char *_sol_hasmntopt(struct mnttab *mnt, const char *opt)
 {
 	struct mntent mnt_new;
 
diff --git a/lib/libspl/include/umem.h b/lib/libspl/include/umem.h
index eee0dc975..288aaf3ec 100644
--- a/lib/libspl/include/umem.h
+++ b/lib/libspl/include/umem.h
@@ -140,7 +140,7 @@ umem_nofail_callback(umem_nofail_callback_t *cb __maybe_unused)
 
 static inline umem_cache_t *
 umem_cache_create(
-    char *name, size_t bufsize, size_t align,
+    const char *name, size_t bufsize, size_t align,
     umem_constructor_t *constructor,
     umem_destructor_t *destructor,
     umem_reclaim_t *reclaim,
diff --git a/lib/libzfs/libzfs_crypto.c b/lib/libzfs/libzfs_crypto.c
index 737b3f4dc..c241aeaa4 100644
--- a/lib/libzfs/libzfs_crypto.c
+++ b/lib/libzfs/libzfs_crypto.c
@@ -849,7 +849,8 @@ encryption_feature_is_enabled(zpool_handle_t *zph)
 static int
 populate_create_encryption_params_nvlists(libzfs_handle_t *hdl,
     zfs_handle_t *zhp, boolean_t newkey, zfs_keyformat_t keyformat,
-    char *keylocation, nvlist_t *props, uint8_t **wkeydata, uint_t *wkeylen)
+    const char *keylocation, nvlist_t *props, uint8_t **wkeydata,
+    uint_t *wkeylen)
 {
 	int ret;
 	uint64_t iters = 0, salt = 0;
@@ -1121,7 +1122,7 @@ zfs_crypto_create(libzfs_handle_t *hdl, char *parent_name, nvlist_t *props,
 
 	/* default to prompt if no keylocation is specified */
 	if (keyformat != ZFS_KEYFORMAT_NONE && keylocation == NULL) {
-		keylocation = "prompt";
+		keylocation = (char *)"prompt";
 		ret = nvlist_add_string(props,
 		    zfs_prop_to_name(ZFS_PROP_KEYLOCATION), keylocation);
 		if (ret != 0)
@@ -1699,7 +1700,7 @@ zfs_crypto_rewrap(zfs_handle_t *zhp, nvlist_t *raw_props, boolean_t inheritkey)
 
 			/* default to prompt if no keylocation is specified */
 			if (keylocation == NULL) {
-				keylocation = "prompt";
+				keylocation = (char *)"prompt";
 				ret = nvlist_add_string(props,
 				    zfs_prop_to_name(ZFS_PROP_KEYLOCATION),
 				    keylocation);
diff --git a/lib/libzfs/libzfs_dataset.c b/lib/libzfs/libzfs_dataset.c
index 24d9b81f4..4e25985a4 100644
--- a/lib/libzfs/libzfs_dataset.c
+++ b/lib/libzfs/libzfs_dataset.c
@@ -882,7 +882,7 @@ libzfs_mnttab_find(libzfs_handle_t *hdl, const char *fsname,
 			return (ENOENT);
 
 		srch.mnt_special = (char *)fsname;
-		srch.mnt_fstype = MNTTYPE_ZFS;
+		srch.mnt_fstype = (char *)MNTTYPE_ZFS;
 		ret = getmntany(mnttab, entry, &srch) ? ENOENT : 0;
 		(void) fclose(mnttab);
 		return (ret);
@@ -2051,7 +2051,7 @@ getprop_uint64(zfs_handle_t *zhp, zfs_prop_t prop, char **source)
 		verify(!zhp->zfs_props_table ||
 		    zhp->zfs_props_table[prop] == B_TRUE);
 		value = zfs_prop_default_numeric(prop);
-		*source = "";
+		*source = (char *)"";
 	}
 
 	return (value);
@@ -2072,7 +2072,7 @@ getprop_string(zfs_handle_t *zhp, zfs_prop_t prop, char **source)
 		verify(!zhp->zfs_props_table ||
 		    zhp->zfs_props_table[prop] == B_TRUE);
 		value = zfs_prop_default_string(prop);
-		*source = "";
+		*source = (char *)"";
 	}
 
 	return (value);
@@ -2114,8 +2114,8 @@ get_numeric_property(zfs_handle_t *zhp, zfs_prop_t prop, zprop_source_t *src,
 	zfs_cmd_t zc = {"\0"};
 	nvlist_t *zplprops = NULL;
 	struct mnttab mnt;
-	char *mntopt_on = NULL;
-	char *mntopt_off = NULL;
+	const char *mntopt_on = NULL;
+	const char *mntopt_off = NULL;
 	boolean_t received = zfs_is_recvd_props_mode(zhp);
 
 	*source = NULL;
@@ -2194,7 +2194,7 @@ get_numeric_property(zfs_handle_t *zhp, zfs_prop_t prop, zprop_source_t *src,
 	}
 
 	if (zhp->zfs_mntopts == NULL)
-		mnt.mnt_mntopts = "";
+		mnt.mnt_mntopts = (char *)"";
 	else
 		mnt.mnt_mntopts = zhp->zfs_mntopts;
 
diff --git a/lib/libzfs/libzfs_impl.h b/lib/libzfs/libzfs_impl.h
index 38104fb5c..878daab3f 100644
--- a/lib/libzfs/libzfs_impl.h
+++ b/lib/libzfs/libzfs_impl.h
@@ -223,7 +223,7 @@ typedef struct differ_info {
 	int datafd;
 } differ_info_t;
 
-extern int do_mount(zfs_handle_t *zhp, const char *mntpt, char *opts,
+extern int do_mount(zfs_handle_t *zhp, const char *mntpt, const char *opts,
     int flags);
 extern int do_unmount(zfs_handle_t *zhp, const char *mntpt, int flags);
 extern int libzfs_load_module(void);
diff --git a/lib/libzfs/libzfs_mount.c b/lib/libzfs/libzfs_mount.c
index a2f1c982c..511552884 100644
--- a/lib/libzfs/libzfs_mount.c
+++ b/lib/libzfs/libzfs_mount.c
@@ -289,7 +289,7 @@ zfs_is_mountable(zfs_handle_t *zhp, char *buf, size_t buflen,
 
 static int
 zfs_add_option(zfs_handle_t *zhp, char *options, int len,
-    zfs_prop_t prop, char *on, char *off)
+    zfs_prop_t prop, const char *on, const char *off)
 {
 	char *source;
 	uint64_t value;
diff --git a/lib/libzfs/libzfs_pool.c b/lib/libzfs/libzfs_pool.c
index 8333e0e78..375abb944 100644
--- a/lib/libzfs/libzfs_pool.c
+++ b/lib/libzfs/libzfs_pool.c
@@ -119,7 +119,7 @@ zpool_get_prop_string(zpool_handle_t *zhp, zpool_prop_t prop,
     zprop_source_t *src)
 {
 	nvlist_t *nv, *nvl;
-	char *value;
+	const char *value;
 	zprop_source_t source;
 
 	nvl = zhp->zpool_props;
@@ -128,7 +128,7 @@ zpool_get_prop_string(zpool_handle_t *zhp, zpool_prop_t prop,
 		value = fnvlist_lookup_string(nv, ZPROP_VALUE);
 	} else {
 		source = ZPROP_SRC_DEFAULT;
-		if ((value = (char *)zpool_prop_default_string(prop)) == NULL)
+		if ((value = zpool_prop_default_string(prop)) == NULL)
 			value = "-";
 	}
 
@@ -2111,7 +2111,7 @@ zpool_import_props(libzfs_handle_t *hdl, nvlist_t *config, const char *newname,
 		case EREMOTEIO:
 			if (nv != NULL && nvlist_lookup_nvlist(nv,
 			    ZPOOL_CONFIG_LOAD_INFO, &nvinfo) == 0) {
-				char *hostname = "<unknown>";
+				const char *hostname = "<unknown>";
 				uint64_t hostid = 0;
 				mmp_state_t mmp_state;
 
@@ -5029,7 +5029,7 @@ zpool_get_vdev_prop_value(nvlist_t *nvprop, vdev_prop_t prop, char *prop_name,
     char *buf, size_t len, zprop_source_t *srctype, boolean_t literal)
 {
 	nvlist_t *nv;
-	char *strval;
+	const char *strval;
 	uint64_t intval;
 	zprop_source_t src = ZPROP_SRC_NONE;
 
@@ -5059,8 +5059,7 @@ zpool_get_vdev_prop_value(nvlist_t *nvprop, vdev_prop_t prop, char *prop_name,
 			strval = fnvlist_lookup_string(nv, ZPROP_VALUE);
 		} else {
 			src = ZPROP_SRC_DEFAULT;
-			if ((strval = (char *)vdev_prop_default_string(prop))
-			    == NULL)
+			if ((strval = vdev_prop_default_string(prop)) == NULL)
 				strval = "-";
 		}
 		(void) strlcpy(buf, strval, len);
diff --git a/lib/libzfs/libzfs_sendrecv.c b/lib/libzfs/libzfs_sendrecv.c
index f50253299..794aff5fe 100644
--- a/lib/libzfs/libzfs_sendrecv.c
+++ b/lib/libzfs/libzfs_sendrecv.c
@@ -2065,7 +2065,7 @@ send_prelim_records(zfs_handle_t *zhp, const char *from, int fd,
 	/* name of filesystem/volume that contains snapshot we are sending */
 	char tofs[ZFS_MAX_DATASET_NAME_LEN];
 	/* short name of snap we are sending */
-	char *tosnap = "";
+	const char *tosnap = "";
 
 	char errbuf[ERRBUFLEN];
 	(void) snprintf(errbuf, sizeof (errbuf), dgettext(TEXT_DOMAIN,
diff --git a/lib/libzfs/libzfs_status.c b/lib/libzfs/libzfs_status.c
index 348a09361..9f450806d 100644
--- a/lib/libzfs/libzfs_status.c
+++ b/lib/libzfs/libzfs_status.c
@@ -56,7 +56,7 @@
  * in include/libzfs.h.  Note that there are some status results which go past
  * the end of this table, and hence have no associated message ID.
  */
-static char *zfs_msgid_table[] = {
+static const char *const zfs_msgid_table[] = {
 	"ZFS-8000-14", /* ZPOOL_STATUS_CORRUPT_CACHE */
 	"ZFS-8000-2Q", /* ZPOOL_STATUS_MISSING_DEV_R */
 	"ZFS-8000-3C", /* ZPOOL_STATUS_MISSING_DEV_NR */
@@ -495,7 +495,8 @@ check_status(nvlist_t *config, boolean_t isimport,
 }
 
 zpool_status_t
-zpool_get_status(zpool_handle_t *zhp, char **msgid, zpool_errata_t *errata)
+zpool_get_status(zpool_handle_t *zhp, const char **msgid,
+    zpool_errata_t *errata)
 {
 	/*
 	 * pass in the desired feature set, as
@@ -519,7 +520,8 @@ zpool_get_status(zpool_handle_t *zhp, char **msgid, zpool_errata_t *errata)
 }
 
 zpool_status_t
-zpool_import_status(nvlist_t *config, char **msgid, zpool_errata_t *errata)
+zpool_import_status(nvlist_t *config, const char **msgid,
+    zpool_errata_t *errata)
 {
 	zpool_status_t ret = check_status(config, B_TRUE, errata, NULL);
 
diff --git a/lib/libzfs/libzfs_util.c b/lib/libzfs/libzfs_util.c
index 3ab82c350..4adaab86e 100644
--- a/lib/libzfs/libzfs_util.c
+++ b/lib/libzfs/libzfs_util.c
@@ -999,16 +999,13 @@ libzfs_free_str_array(char **strs, int count)
  *
  * Returns 0 otherwise.
  */
-int
-libzfs_envvar_is_set(char *envvar)
+boolean_t
+libzfs_envvar_is_set(const char *envvar)
 {
 	char *env = getenv(envvar);
-	if (env && (strtoul(env, NULL, 0) > 0 ||
+	return (env && (strtoul(env, NULL, 0) > 0 ||
 	    (!strncasecmp(env, "YES", 3) && strnlen(env, 4) == 3) ||
-	    (!strncasecmp(env, "ON", 2) && strnlen(env, 3) == 2)))
-		return (1);
-
-	return (0);
+	    (!strncasecmp(env, "ON", 2) && strnlen(env, 3) == 2)));
 }
 
 libzfs_handle_t *
@@ -2002,22 +1999,22 @@ use_color(void)
  * color_end();
  */
 void
-color_start(char *color)
+color_start(const char *color)
 {
 	if (use_color())
-		printf("%s", color);
+		fputs(color, stdout);
 }
 
 void
 color_end(void)
 {
 	if (use_color())
-		printf(ANSI_RESET);
+		fputs(ANSI_RESET, stdout);
 }
 
 /* printf() with a color.  If color is NULL, then do a normal printf. */
 int
-printf_color(char *color, char *format, ...)
+printf_color(const char *color, const char *format, ...)
 {
 	va_list aptr;
 	int rc;
diff --git a/lib/libzfs/os/freebsd/libzfs_zmount.c b/lib/libzfs/os/freebsd/libzfs_zmount.c
index 3a6ab43e9..0d2bd5d51 100644
--- a/lib/libzfs/os/freebsd/libzfs_zmount.c
+++ b/lib/libzfs/os/freebsd/libzfs_zmount.c
@@ -74,7 +74,7 @@ build_iovec(struct iovec **iov, int *iovlen, const char *name, void *val,
 }
 
 static int
-do_mount_(const char *spec, const char *dir, int mflag, char *fstype,
+do_mount_(const char *spec, const char *dir, int mflag,
     char *dataptr, int datalen, char *optptr, int optlen)
 {
 	struct iovec *iov;
@@ -83,8 +83,6 @@ do_mount_(const char *spec, const char *dir, int mflag, char *fstype,
 
 	assert(spec != NULL);
 	assert(dir != NULL);
-	assert(fstype != NULL);
-	assert(strcmp(fstype, MNTTYPE_ZFS) == 0);
 	assert(dataptr == NULL), (void) dataptr;
 	assert(datalen == 0), (void) datalen;
 	assert(optptr != NULL);
@@ -99,7 +97,8 @@ do_mount_(const char *spec, const char *dir, int mflag, char *fstype,
 		build_iovec(&iov, &iovlen, "update", NULL, 0);
 	if (mflag & MS_RDONLY)
 		build_iovec(&iov, &iovlen, "ro", NULL, 0);
-	build_iovec(&iov, &iovlen, "fstype", fstype, (size_t)-1);
+	build_iovec(&iov, &iovlen, "fstype", __DECONST(char *, MNTTYPE_ZFS),
+	    (size_t)-1);
 	build_iovec(&iov, &iovlen, "fspath", __DECONST(char *, dir),
 	    (size_t)-1);
 	build_iovec(&iov, &iovlen, "from", __DECONST(char *, spec), (size_t)-1);
@@ -113,10 +112,10 @@ do_mount_(const char *spec, const char *dir, int mflag, char *fstype,
 }
 
 int
-do_mount(zfs_handle_t *zhp, const char *mntpt, char *opts, int flags)
+do_mount(zfs_handle_t *zhp, const char *mntpt, const char *opts, int flags)
 {
 
-	return (do_mount_(zfs_get_name(zhp), mntpt, flags, MNTTYPE_ZFS, NULL, 0,
+	return (do_mount_(zfs_get_name(zhp), mntpt, flags, NULL, 0,
 	    opts, sizeof (mntpt)));
 }
 
diff --git a/lib/libzfs/os/linux/libzfs_mount_os.c b/lib/libzfs/os/linux/libzfs_mount_os.c
index eab068d59..299d3a66e 100644
--- a/lib/libzfs/os/linux/libzfs_mount_os.c
+++ b/lib/libzfs/os/linux/libzfs_mount_os.c
@@ -180,7 +180,7 @@ out:
  * otherwise they are considered fatal are copied in to badopt.
  */
 int
-zfs_parse_mount_options(char *mntopts, unsigned long *mntflags,
+zfs_parse_mount_options(const char *mntopts, unsigned long *mntflags,
     unsigned long *zfsflags, int sloppy, char *badopt, char *mtabopt)
 {
 	int error = 0, quote = 0, flag = 0, count = 0;
@@ -320,7 +320,7 @@ zfs_adjust_mount_options(zfs_handle_t *zhp, const char *mntpoint,
  * make due with return value from the mount process.
  */
 int
-do_mount(zfs_handle_t *zhp, const char *mntpt, char *opts, int flags)
+do_mount(zfs_handle_t *zhp, const char *mntpt, const char *opts, int flags)
 {
 	const char *src = zfs_get_name(zhp);
 	int error = 0;
@@ -341,10 +341,10 @@ do_mount(zfs_handle_t *zhp, const char *mntpt, char *opts, int flags)
 		}
 	} else {
 		char *argv[9] = {
-		    "/bin/mount",
-		    "--no-canonicalize",
-		    "-t", MNTTYPE_ZFS,
-		    "-o", opts,
+		    (char *)"/bin/mount",
+		    (char *)"--no-canonicalize",
+		    (char *)"-t", (char *)MNTTYPE_ZFS,
+		    (char *)"-o", (char *)opts,
 		    (char *)src,
 		    (char *)mntpt,
 		    (char *)NULL };
@@ -384,23 +384,17 @@ do_unmount(zfs_handle_t *zhp, const char *mntpt, int flags)
 		return (rv < 0 ? errno : 0);
 	}
 
-	char force_opt[] = "-f";
-	char lazy_opt[] = "-l";
 	char *argv[7] = {
-	    "/bin/umount",
-	    "-t", MNTTYPE_ZFS,
+	    (char *)"/bin/umount",
+	    (char *)"-t", (char *)MNTTYPE_ZFS,
 	    NULL, NULL, NULL, NULL };
 	int rc, count = 3;
 
-	if (flags & MS_FORCE) {
-		argv[count] = force_opt;
-		count++;
-	}
+	if (flags & MS_FORCE)
+		argv[count++] = (char *)"-f";
 
-	if (flags & MS_DETACH) {
-		argv[count] = lazy_opt;
-		count++;
-	}
+	if (flags & MS_DETACH)
+		argv[count++] = (char *)"-l";
 
 	argv[count] = (char *)mntpt;
 	rc = libzfs_run_process(argv[0], argv, STDOUT_VERBOSE|STDERR_VERBOSE);
diff --git a/lib/libzfs/os/linux/libzfs_util_os.c b/lib/libzfs/os/linux/libzfs_util_os.c
index 0ab79be4e..ec62b003c 100644
--- a/lib/libzfs/os/linux/libzfs_util_os.c
+++ b/lib/libzfs/os/linux/libzfs_util_os.c
@@ -99,7 +99,7 @@ libzfs_load_module(void)
 		return (0);
 
 	if (access(ZFS_SYSFS_DIR, F_OK) != 0) {
-		char *argv[] = {"modprobe", "zfs", NULL};
+		char *argv[] = {(char *)"modprobe", (char *)"zfs", NULL};
 		if (libzfs_run_process("modprobe", argv, 0))
 			return (ENOEXEC);
 
diff --git a/lib/libzpool/kernel.c b/lib/libzpool/kernel.c
index 011f9d211..05c278f91 100644
--- a/lib/libzpool/kernel.c
+++ b/lib/libzpool/kernel.c
@@ -1002,8 +1002,6 @@ kmem_cache_reap_active(void)
 	return (0);
 }
 
-void *zvol_tag = "zvol_tag";
-
 void
 zvol_create_minor(const char *name)
 {
diff --git a/lib/libzpool/util.c b/lib/libzpool/util.c
index b9ee52a61..9a6326e42 100644
--- a/lib/libzpool/util.c
+++ b/lib/libzpool/util.c
@@ -64,7 +64,8 @@ show_vdev_stats(const char *desc, const char *ctype, nvlist_t *nv, int indent)
 	}
 
 	if (desc != NULL) {
-		char *suffix = "", *bias = NULL;
+		const char *suffix = "";
+		char *bias = NULL;
 		char bias_suffix[32];
 
 		(void) nvlist_lookup_uint64(nv, ZPOOL_CONFIG_IS_LOG, &is_log);
@@ -117,7 +118,7 @@ show_vdev_stats(const char *desc, const char *ctype, nvlist_t *nv, int indent)
 		int len;
 		if (nvlist_lookup_string(cnv, ZPOOL_CONFIG_PATH, &cname) &&
 		    nvlist_lookup_string(cnv, ZPOOL_CONFIG_TYPE, &cname))
-			cname = "<unknown>";
+			cname = (char *)"<unknown>";
 		len = strlen(cname) + 2;
 		tname = umem_zalloc(len, UMEM_NOFAIL);
 		(void) strlcpy(tname, cname, len);
diff --git a/lib/libzutil/os/linux/zutil_import_os.c b/lib/libzutil/os/linux/zutil_import_os.c
index 6b825fcd7..85f367237 100644
--- a/lib/libzutil/os/linux/zutil_import_os.c
+++ b/lib/libzutil/os/linux/zutil_import_os.c
@@ -328,7 +328,9 @@ zpool_find_import_blkid(libpc_handle_t *hdl, pthread_mutex_t *lock,
 		return (EINVAL);
 	}
 
-	error = blkid_dev_set_search(iter, "TYPE", "zfs_member");
+	/* Only const char *s since 2.32 */
+	error = blkid_dev_set_search(iter,
+	    (char *)"TYPE", (char *)"zfs_member");
 	if (error != 0) {
 		blkid_dev_iterate_end(iter);
 		blkid_put_cache(cache);
diff --git a/lib/libzutil/zutil_import.c b/lib/libzutil/zutil_import.c
index 3744a1c34..26fba2cad 100644
--- a/lib/libzutil/zutil_import.c
+++ b/lib/libzutil/zutil_import.c
@@ -1543,7 +1543,7 @@ discover_cached_paths(libpc_handle_t *hdl, nvlist_t *nv,
 	 */
 	if (nvlist_lookup_string(nv, ZPOOL_CONFIG_PATH, &path) == 0) {
 		if ((dl = zfs_dirnamelen(path)) == -1)
-			path = ".";
+			path = (char *)".";
 		else
 			path[dl] = '\0';
 		return (zpool_find_import_scan_dir(hdl, lock, cache,
diff --git a/module/icp/algs/aes/aes_impl.c b/module/icp/algs/aes/aes_impl.c
index f518a54a6..16afc2572 100644
--- a/module/icp/algs/aes/aes_impl.c
+++ b/module/icp/algs/aes/aes_impl.c
@@ -337,7 +337,7 @@ aes_impl_init(void)
 }
 
 static const struct {
-	char *name;
+	const char *name;
 	uint32_t sel;
 } aes_impl_opts[] = {
 		{ "cycle",	IMPL_CYCLE },
diff --git a/module/icp/algs/modes/gcm.c b/module/icp/algs/modes/gcm.c
index ee2100b7f..e6a631c1a 100644
--- a/module/icp/algs/modes/gcm.c
+++ b/module/icp/algs/modes/gcm.c
@@ -907,7 +907,7 @@ gcm_impl_init(void)
 }
 
 static const struct {
-	char *name;
+	const char *name;
 	uint32_t sel;
 } gcm_impl_opts[] = {
 		{ "cycle",	IMPL_CYCLE },
diff --git a/module/os/freebsd/spl/spl_kmem.c b/module/os/freebsd/spl/spl_kmem.c
index ee8f1d851..ca9a67756 100644
--- a/module/os/freebsd/spl/spl_kmem.c
+++ b/module/os/freebsd/spl/spl_kmem.c
@@ -156,7 +156,7 @@ kmem_std_destructor(void *mem, int size __unused, void *private)
 }
 
 kmem_cache_t *
-kmem_cache_create(char *name, size_t bufsize, size_t align,
+kmem_cache_create(const char *name, size_t bufsize, size_t align,
     int (*constructor)(void *, void *, int), void (*destructor)(void *, void *),
     void (*reclaim)(void *) __unused, void *private, vmem_t *vmp, int cflags)
 {
diff --git a/module/os/linux/spl/spl-kmem-cache.c b/module/os/linux/spl/spl-kmem-cache.c
index 33aaad653..ba4ca49a2 100644
--- a/module/os/linux/spl/spl-kmem-cache.c
+++ b/module/os/linux/spl/spl-kmem-cache.c
@@ -679,7 +679,7 @@ spl_magazine_destroy(spl_kmem_cache_t *skc)
  *	KMC_NODEBUG	Disable debugging (unsupported)
  */
 spl_kmem_cache_t *
-spl_kmem_cache_create(char *name, size_t size, size_t align,
+spl_kmem_cache_create(const char *name, size_t size, size_t align,
     spl_kmem_ctor_t ctor, spl_kmem_dtor_t dtor, void *reclaim,
     void *priv, void *vmp, int flags)
 {
diff --git a/module/zcommon/zfs_comutil.c b/module/zcommon/zfs_comutil.c
index 020e7e86c..c8f4dccd3 100644
--- a/module/zcommon/zfs_comutil.c
+++ b/module/zcommon/zfs_comutil.c
@@ -68,7 +68,7 @@ zfs_allocatable_devs(nvlist_t *nv)
  * Are there special vdevs?
  */
 boolean_t
-zfs_special_devs(nvlist_t *nv, char *type)
+zfs_special_devs(nvlist_t *nv, const char *type)
 {
 	char *bias;
 	uint_t c;
@@ -84,11 +84,9 @@ zfs_special_devs(nvlist_t *nv, char *type)
 		    &bias) == 0) {
 			if (strcmp(bias, VDEV_ALLOC_BIAS_SPECIAL) == 0 ||
 			    strcmp(bias, VDEV_ALLOC_BIAS_DEDUP) == 0) {
-				if (type != NULL && strcmp(bias, type) == 0) {
+				if (type == NULL ||
+				    (type != NULL && strcmp(bias, type) == 0))
 					return (B_TRUE);
-				} else if (type == NULL) {
-					return (B_TRUE);
-				}
 			}
 		}
 	}
diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index af42670cc..919081c25 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -2280,7 +2280,7 @@ arc_evictable_space_decrement(arc_buf_hdr_t *hdr, arc_state_t *state)
  * it is not evictable.
  */
 static void
-add_reference(arc_buf_hdr_t *hdr, void *tag)
+add_reference(arc_buf_hdr_t *hdr, const void *tag)
 {
 	arc_state_t *state;
 
@@ -2740,8 +2740,8 @@ arc_can_share(arc_buf_hdr_t *hdr, arc_buf_t *buf)
  */
 static int
 arc_buf_alloc_impl(arc_buf_hdr_t *hdr, spa_t *spa, const zbookmark_phys_t *zb,
-    void *tag, boolean_t encrypted, boolean_t compressed, boolean_t noauth,
-    boolean_t fill, arc_buf_t **ret)
+    const void *tag, boolean_t encrypted, boolean_t compressed,
+    boolean_t noauth, boolean_t fill, arc_buf_t **ret)
 {
 	arc_buf_t *buf;
 	arc_fill_flags_t flags = ARC_FILL_LOCKED;
@@ -2841,7 +2841,7 @@ arc_buf_alloc_impl(arc_buf_hdr_t *hdr, spa_t *spa, const zbookmark_phys_t *zb,
 	return (0);
 }
 
-static char *arc_onloan_tag = "onloan";
+static const char *arc_onloan_tag = "onloan";
 
 static inline void
 arc_loaned_bytes_update(int64_t delta)
@@ -3589,7 +3589,8 @@ arc_convert_to_raw(arc_buf_t *buf, uint64_t dsobj, boolean_t byteorder,
  * The buf is returned thawed since we expect the consumer to modify it.
  */
 arc_buf_t *
-arc_alloc_buf(spa_t *spa, void *tag, arc_buf_contents_t type, int32_t size)
+arc_alloc_buf(spa_t *spa, const void *tag, arc_buf_contents_t type,
+    int32_t size)
 {
 	arc_buf_hdr_t *hdr = arc_hdr_alloc(spa_load_guid(spa), size, size,
 	    B_FALSE, ZIO_COMPRESS_OFF, 0, type);
@@ -3607,8 +3608,8 @@ arc_alloc_buf(spa_t *spa, void *tag, arc_buf_contents_t type, int32_t size)
  * for bufs containing metadata.
  */
 arc_buf_t *
-arc_alloc_compressed_buf(spa_t *spa, void *tag, uint64_t psize, uint64_t lsize,
-    enum zio_compress compression_type, uint8_t complevel)
+arc_alloc_compressed_buf(spa_t *spa, const void *tag, uint64_t psize,
+    uint64_t lsize, enum zio_compress compression_type, uint8_t complevel)
 {
 	ASSERT3U(lsize, >, 0);
 	ASSERT3U(lsize, >=, psize);
@@ -3635,9 +3636,9 @@ arc_alloc_compressed_buf(spa_t *spa, void *tag, uint64_t psize, uint64_t lsize,
 }
 
 arc_buf_t *
-arc_alloc_raw_buf(spa_t *spa, void *tag, uint64_t dsobj, boolean_t byteorder,
-    const uint8_t *salt, const uint8_t *iv, const uint8_t *mac,
-    dmu_object_type_t ot, uint64_t psize, uint64_t lsize,
+arc_alloc_raw_buf(spa_t *spa, const void *tag, uint64_t dsobj,
+    boolean_t byteorder, const uint8_t *salt, const uint8_t *iv,
+    const uint8_t *mac, dmu_object_type_t ot, uint64_t psize, uint64_t lsize,
     enum zio_compress compression_type, uint8_t complevel)
 {
 	arc_buf_hdr_t *hdr;
diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c
index d10e87652..00b01611d 100644
--- a/module/zfs/dbuf.c
+++ b/module/zfs/dbuf.c
@@ -1297,7 +1297,7 @@ dbuf_whichblock(const dnode_t *dn, const int64_t level, const uint64_t offset)
  * used when modifying or reading db_blkptr.
  */
 db_lock_type_t
-dmu_buf_lock_parent(dmu_buf_impl_t *db, krw_t rw, void *tag)
+dmu_buf_lock_parent(dmu_buf_impl_t *db, krw_t rw, const void *tag)
 {
 	enum db_lock_type ret = DLT_NONE;
 	if (db->db_parent != NULL) {
@@ -1322,7 +1322,7 @@ dmu_buf_lock_parent(dmu_buf_impl_t *db, krw_t rw, void *tag)
  * panic if we didn't pass the lock type in.
  */
 void
-dmu_buf_unlock_parent(dmu_buf_impl_t *db, db_lock_type_t type, void *tag)
+dmu_buf_unlock_parent(dmu_buf_impl_t *db, db_lock_type_t type, const void *tag)
 {
 	if (type == DLT_PARENT)
 		rw_exit(&db->db_parent->db_rwlock);
@@ -1522,7 +1522,7 @@ dbuf_read_verify_dnode_crypt(dmu_buf_impl_t *db, uint32_t flags)
  */
 static int
 dbuf_read_impl(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags,
-    db_lock_type_t dblt, void *tag)
+    db_lock_type_t dblt, const void *tag)
 {
 	dnode_t *dn;
 	zbookmark_phys_t zb;
@@ -3532,7 +3532,7 @@ dbuf_hold_copy(dnode_t *dn, dmu_buf_impl_t *db)
 int
 dbuf_hold_impl(dnode_t *dn, uint8_t level, uint64_t blkid,
     boolean_t fail_sparse, boolean_t fail_uncached,
-    void *tag, dmu_buf_impl_t **dbp)
+    const void *tag, dmu_buf_impl_t **dbp)
 {
 	dmu_buf_impl_t *db, *parent = NULL;
 
@@ -3637,13 +3637,13 @@ dbuf_hold_impl(dnode_t *dn, uint8_t level, uint64_t blkid,
 }
 
 dmu_buf_impl_t *
-dbuf_hold(dnode_t *dn, uint64_t blkid, void *tag)
+dbuf_hold(dnode_t *dn, uint64_t blkid, const void *tag)
 {
 	return (dbuf_hold_level(dn, 0, blkid, tag));
 }
 
 dmu_buf_impl_t *
-dbuf_hold_level(dnode_t *dn, int level, uint64_t blkid, void *tag)
+dbuf_hold_level(dnode_t *dn, int level, uint64_t blkid, const void *tag)
 {
 	dmu_buf_impl_t *db;
 	int err = dbuf_hold_impl(dn, level, blkid, FALSE, FALSE, tag, &db);
@@ -3684,7 +3684,7 @@ dbuf_rm_spill(dnode_t *dn, dmu_tx_t *tx)
 
 #pragma weak dmu_buf_add_ref = dbuf_add_ref
 void
-dbuf_add_ref(dmu_buf_impl_t *db, void *tag)
+dbuf_add_ref(dmu_buf_impl_t *db, const void *tag)
 {
 	int64_t holds = zfs_refcount_add(&db->db_holds, tag);
 	VERIFY3S(holds, >, 1);
@@ -3693,7 +3693,7 @@ dbuf_add_ref(dmu_buf_impl_t *db, void *tag)
 #pragma weak dmu_buf_try_add_ref = dbuf_try_add_ref
 boolean_t
 dbuf_try_add_ref(dmu_buf_t *db_fake, objset_t *os, uint64_t obj, uint64_t blkid,
-    void *tag)
+    const void *tag)
 {
 	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
 	dmu_buf_impl_t *found_db;
@@ -3722,14 +3722,14 @@ dbuf_try_add_ref(dmu_buf_t *db_fake, objset_t *os, uint64_t obj, uint64_t blkid,
  * dnode's parent dbuf evicting its dnode handles.
  */
 void
-dbuf_rele(dmu_buf_impl_t *db, void *tag)
+dbuf_rele(dmu_buf_impl_t *db, const void *tag)
 {
 	mutex_enter(&db->db_mtx);
 	dbuf_rele_and_unlock(db, tag, B_FALSE);
 }
 
 void
-dmu_buf_rele(dmu_buf_t *db, void *tag)
+dmu_buf_rele(dmu_buf_t *db, const void *tag)
 {
 	dbuf_rele((dmu_buf_impl_t *)db, tag);
 }
@@ -3748,7 +3748,7 @@ dmu_buf_rele(dmu_buf_t *db, void *tag)
  *
  */
 void
-dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag, boolean_t evicting)
+dbuf_rele_and_unlock(dmu_buf_impl_t *db, const void *tag, boolean_t evicting)
 {
 	int64_t holds;
 	uint64_t size;
diff --git a/module/zfs/dmu.c b/module/zfs/dmu.c
index 7d8b2c96b..e6008b3bf 100644
--- a/module/zfs/dmu.c
+++ b/module/zfs/dmu.c
@@ -160,7 +160,7 @@ const dmu_object_byteswap_info_t dmu_ot_byteswap[DMU_BSWAP_NUMFUNCS] = {
 
 static int
 dmu_buf_hold_noread_by_dnode(dnode_t *dn, uint64_t offset,
-    void *tag, dmu_buf_t **dbp)
+    const void *tag, dmu_buf_t **dbp)
 {
 	uint64_t blkid;
 	dmu_buf_impl_t *db;
@@ -180,7 +180,7 @@ dmu_buf_hold_noread_by_dnode(dnode_t *dn, uint64_t offset,
 }
 int
 dmu_buf_hold_noread(objset_t *os, uint64_t object, uint64_t offset,
-    void *tag, dmu_buf_t **dbp)
+    const void *tag, dmu_buf_t **dbp)
 {
 	dnode_t *dn;
 	uint64_t blkid;
@@ -207,7 +207,7 @@ dmu_buf_hold_noread(objset_t *os, uint64_t object, uint64_t offset,
 
 int
 dmu_buf_hold_by_dnode(dnode_t *dn, uint64_t offset,
-    void *tag, dmu_buf_t **dbp, int flags)
+    const void *tag, dmu_buf_t **dbp, int flags)
 {
 	int err;
 	int db_flags = DB_RF_CANFAIL;
@@ -232,7 +232,7 @@ dmu_buf_hold_by_dnode(dnode_t *dn, uint64_t offset,
 
 int
 dmu_buf_hold(objset_t *os, uint64_t object, uint64_t offset,
-    void *tag, dmu_buf_t **dbp, int flags)
+    const void *tag, dmu_buf_t **dbp, int flags)
 {
 	int err;
 	int db_flags = DB_RF_CANFAIL;
@@ -342,7 +342,7 @@ dmu_rm_spill(objset_t *os, uint64_t object, dmu_tx_t *tx)
  * has not yet been allocated a new bonus dbuf a will be allocated.
  * Returns ENOENT, EIO, or 0.
  */
-int dmu_bonus_hold_by_dnode(dnode_t *dn, void *tag, dmu_buf_t **dbp,
+int dmu_bonus_hold_by_dnode(dnode_t *dn, const void *tag, dmu_buf_t **dbp,
     uint32_t flags)
 {
 	dmu_buf_impl_t *db;
@@ -389,7 +389,7 @@ int dmu_bonus_hold_by_dnode(dnode_t *dn, void *tag, dmu_buf_t **dbp,
 }
 
 int
-dmu_bonus_hold(objset_t *os, uint64_t object, void *tag, dmu_buf_t **dbp)
+dmu_bonus_hold(objset_t *os, uint64_t object, const void *tag, dmu_buf_t **dbp)
 {
 	dnode_t *dn;
 	int error;
@@ -414,7 +414,8 @@ dmu_bonus_hold(objset_t *os, uint64_t object, void *tag, dmu_buf_t **dbp)
  * dmu_spill_hold_existing() should be used.
  */
 int
-dmu_spill_hold_by_dnode(dnode_t *dn, uint32_t flags, void *tag, dmu_buf_t **dbp)
+dmu_spill_hold_by_dnode(dnode_t *dn, uint32_t flags, const void *tag,
+    dmu_buf_t **dbp)
 {
 	dmu_buf_impl_t *db = NULL;
 	int err;
@@ -442,7 +443,7 @@ dmu_spill_hold_by_dnode(dnode_t *dn, uint32_t flags, void *tag, dmu_buf_t **dbp)
 }
 
 int
-dmu_spill_hold_existing(dmu_buf_t *bonus, void *tag, dmu_buf_t **dbp)
+dmu_spill_hold_existing(dmu_buf_t *bonus, const void *tag, dmu_buf_t **dbp)
 {
 	dmu_buf_impl_t *db = (dmu_buf_impl_t *)bonus;
 	dnode_t *dn;
@@ -471,7 +472,7 @@ dmu_spill_hold_existing(dmu_buf_t *bonus, void *tag, dmu_buf_t **dbp)
 }
 
 int
-dmu_spill_hold_by_bonus(dmu_buf_t *bonus, uint32_t flags, void *tag,
+dmu_spill_hold_by_bonus(dmu_buf_t *bonus, uint32_t flags, const void *tag,
     dmu_buf_t **dbp)
 {
 	dmu_buf_impl_t *db = (dmu_buf_impl_t *)bonus;
@@ -498,7 +499,8 @@ dmu_spill_hold_by_bonus(dmu_buf_t *bonus, uint32_t flags, void *tag,
  */
 int
 dmu_buf_hold_array_by_dnode(dnode_t *dn, uint64_t offset, uint64_t length,
-    boolean_t read, void *tag, int *numbufsp, dmu_buf_t ***dbpp, uint32_t flags)
+    boolean_t read, const void *tag, int *numbufsp, dmu_buf_t ***dbpp,
+    uint32_t flags)
 {
 	dmu_buf_t **dbp;
 	zstream_t *zs = NULL;
@@ -619,7 +621,8 @@ dmu_buf_hold_array_by_dnode(dnode_t *dn, uint64_t offset, uint64_t length,
 
 int
 dmu_buf_hold_array(objset_t *os, uint64_t object, uint64_t offset,
-    uint64_t length, int read, void *tag, int *numbufsp, dmu_buf_t ***dbpp)
+    uint64_t length, int read, const void *tag, int *numbufsp,
+    dmu_buf_t ***dbpp)
 {
 	dnode_t *dn;
 	int err;
@@ -638,7 +641,7 @@ dmu_buf_hold_array(objset_t *os, uint64_t object, uint64_t offset,
 
 int
 dmu_buf_hold_array_by_bonus(dmu_buf_t *db_fake, uint64_t offset,
-    uint64_t length, boolean_t read, void *tag, int *numbufsp,
+    uint64_t length, boolean_t read, const void *tag, int *numbufsp,
     dmu_buf_t ***dbpp)
 {
 	dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
@@ -655,7 +658,7 @@ dmu_buf_hold_array_by_bonus(dmu_buf_t *db_fake, uint64_t offset,
 }
 
 void
-dmu_buf_rele_array(dmu_buf_t **dbp_fake, int numbufs, void *tag)
+dmu_buf_rele_array(dmu_buf_t **dbp_fake, int numbufs, const void *tag)
 {
 	int i;
 	dmu_buf_impl_t **dbp = (dmu_buf_impl_t **)dbp_fake;
diff --git a/module/zfs/dmu_object.c b/module/zfs/dmu_object.c
index 12cdbd68b..d954c7d9b 100644
--- a/module/zfs/dmu_object.c
+++ b/module/zfs/dmu_object.c
@@ -46,7 +46,7 @@ int dmu_object_alloc_chunk_shift = 7;
 static uint64_t
 dmu_object_alloc_impl(objset_t *os, dmu_object_type_t ot, int blocksize,
     int indirect_blockshift, dmu_object_type_t bonustype, int bonuslen,
-    int dnodesize, dnode_t **allocated_dnode, void *tag, dmu_tx_t *tx)
+    int dnodesize, dnode_t **allocated_dnode, const void *tag, dmu_tx_t *tx)
 {
 	uint64_t object;
 	uint64_t L1_dnode_count = DNODES_PER_BLOCK <<
@@ -255,7 +255,7 @@ dmu_object_alloc_dnsize(objset_t *os, dmu_object_type_t ot, int blocksize,
 uint64_t
 dmu_object_alloc_hold(objset_t *os, dmu_object_type_t ot, int blocksize,
     int indirect_blockshift, dmu_object_type_t bonustype, int bonuslen,
-    int dnodesize, dnode_t **allocated_dnode, void *tag, dmu_tx_t *tx)
+    int dnodesize, dnode_t **allocated_dnode, const void *tag, dmu_tx_t *tx)
 {
 	return (dmu_object_alloc_impl(os, ot, blocksize, indirect_blockshift,
 	    bonustype, bonuslen, dnodesize, allocated_dnode, tag, tx));
diff --git a/module/zfs/dmu_objset.c b/module/zfs/dmu_objset.c
index 97a81ed8d..324ee8d83 100644
--- a/module/zfs/dmu_objset.c
+++ b/module/zfs/dmu_objset.c
@@ -714,7 +714,7 @@ dmu_objset_from_ds(dsl_dataset_t *ds, objset_t **osp)
  * can be held at a time.
  */
 int
-dmu_objset_hold_flags(const char *name, boolean_t decrypt, void *tag,
+dmu_objset_hold_flags(const char *name, boolean_t decrypt, const void *tag,
     objset_t **osp)
 {
 	dsl_pool_t *dp;
@@ -742,14 +742,14 @@ dmu_objset_hold_flags(const char *name, boolean_t decrypt, void *tag,
 }
 
 int
-dmu_objset_hold(const char *name, void *tag, objset_t **osp)
+dmu_objset_hold(const char *name, const void *tag, objset_t **osp)
 {
 	return (dmu_objset_hold_flags(name, B_FALSE, tag, osp));
 }
 
 static int
 dmu_objset_own_impl(dsl_dataset_t *ds, dmu_objset_type_t type,
-    boolean_t readonly, boolean_t decrypt, void *tag, objset_t **osp)
+    boolean_t readonly, boolean_t decrypt, const void *tag, objset_t **osp)
 {
 	(void) tag;
 
@@ -789,7 +789,7 @@ dmu_objset_own_impl(dsl_dataset_t *ds, dmu_objset_type_t type,
  */
 int
 dmu_objset_own(const char *name, dmu_objset_type_t type,
-    boolean_t readonly, boolean_t decrypt, void *tag, objset_t **osp)
+    boolean_t readonly, boolean_t decrypt, const void *tag, objset_t **osp)
 {
 	dsl_pool_t *dp;
 	dsl_dataset_t *ds;
@@ -834,7 +834,7 @@ dmu_objset_own(const char *name, dmu_objset_type_t type,
 
 int
 dmu_objset_own_obj(dsl_pool_t *dp, uint64_t obj, dmu_objset_type_t type,
-    boolean_t readonly, boolean_t decrypt, void *tag, objset_t **osp)
+    boolean_t readonly, boolean_t decrypt, const void *tag, objset_t **osp)
 {
 	dsl_dataset_t *ds;
 	int err;
@@ -855,7 +855,7 @@ dmu_objset_own_obj(dsl_pool_t *dp, uint64_t obj, dmu_objset_type_t type,
 }
 
 void
-dmu_objset_rele_flags(objset_t *os, boolean_t decrypt, void *tag)
+dmu_objset_rele_flags(objset_t *os, boolean_t decrypt, const void *tag)
 {
 	ds_hold_flags_t flags;
 	dsl_pool_t *dp = dmu_objset_pool(os);
@@ -866,7 +866,7 @@ dmu_objset_rele_flags(objset_t *os, boolean_t decrypt, void *tag)
 }
 
 void
-dmu_objset_rele(objset_t *os, void *tag)
+dmu_objset_rele(objset_t *os, const void *tag)
 {
 	dmu_objset_rele_flags(os, B_FALSE, tag);
 }
@@ -884,7 +884,7 @@ dmu_objset_rele(objset_t *os, void *tag)
  */
 void
 dmu_objset_refresh_ownership(dsl_dataset_t *ds, dsl_dataset_t **newds,
-    boolean_t decrypt, void *tag)
+    boolean_t decrypt, const void *tag)
 {
 	dsl_pool_t *dp;
 	char name[ZFS_MAX_DATASET_NAME_LEN];
@@ -904,7 +904,7 @@ dmu_objset_refresh_ownership(dsl_dataset_t *ds, dsl_dataset_t **newds,
 }
 
 void
-dmu_objset_disown(objset_t *os, boolean_t decrypt, void *tag)
+dmu_objset_disown(objset_t *os, boolean_t decrypt, const void *tag)
 {
 	ds_hold_flags_t flags;
 
diff --git a/module/zfs/dmu_recv.c b/module/zfs/dmu_recv.c
index c90df1eb4..5ac862519 100644
--- a/module/zfs/dmu_recv.c
+++ b/module/zfs/dmu_recv.c
@@ -68,7 +68,7 @@ static int zfs_recv_queue_length = SPA_MAXBLOCKSIZE;
 static int zfs_recv_queue_ff = 20;
 static int zfs_recv_write_batch_size = 1024 * 1024;
 
-static void *const dmu_recv_tag = "dmu_recv_tag";
+static const void *const dmu_recv_tag = "dmu_recv_tag";
 const char *const recv_clone_name = "%recv";
 
 static int receive_read_payload_and_next_header(dmu_recv_cookie_t *ra, int len,
diff --git a/module/zfs/dnode.c b/module/zfs/dnode.c
index af0ee1b0f..39e9ca1b8 100644
--- a/module/zfs/dnode.c
+++ b/module/zfs/dnode.c
@@ -1268,7 +1268,7 @@ dnode_buf_evict_async(void *dbu)
  */
 int
 dnode_hold_impl(objset_t *os, uint64_t object, int flag, int slots,
-    void *tag, dnode_t **dnp)
+    const void *tag, dnode_t **dnp)
 {
 	int epb, idx, err;
 	int drop_struct_lock = FALSE;
@@ -1562,7 +1562,7 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag, int slots,
  * Return held dnode if the object is allocated, NULL if not.
  */
 int
-dnode_hold(objset_t *os, uint64_t object, void *tag, dnode_t **dnp)
+dnode_hold(objset_t *os, uint64_t object, const void *tag, dnode_t **dnp)
 {
 	return (dnode_hold_impl(os, object, DNODE_MUST_BE_ALLOCATED, 0, tag,
 	    dnp));
@@ -1574,7 +1574,7 @@ dnode_hold(objset_t *os, uint64_t object, void *tag, dnode_t **dnp)
  * new reference.
  */
 boolean_t
-dnode_add_ref(dnode_t *dn, void *tag)
+dnode_add_ref(dnode_t *dn, const void *tag)
 {
 	mutex_enter(&dn->dn_mtx);
 	if (zfs_refcount_is_zero(&dn->dn_holds)) {
@@ -1587,14 +1587,14 @@ dnode_add_ref(dnode_t *dn, void *tag)
 }
 
 void
-dnode_rele(dnode_t *dn, void *tag)
+dnode_rele(dnode_t *dn, const void *tag)
 {
 	mutex_enter(&dn->dn_mtx);
 	dnode_rele_and_unlock(dn, tag, B_FALSE);
 }
 
 void
-dnode_rele_and_unlock(dnode_t *dn, void *tag, boolean_t evicting)
+dnode_rele_and_unlock(dnode_t *dn, const void *tag, boolean_t evicting)
 {
 	uint64_t refs;
 	/* Get while the hold prevents the dnode from moving. */
@@ -2029,7 +2029,7 @@ dnode_dirty_l1range(dnode_t *dn, uint64_t start_blkid, uint64_t end_blkid,
 }
 
 void
-dnode_set_dirtyctx(dnode_t *dn, dmu_tx_t *tx, void *tag)
+dnode_set_dirtyctx(dnode_t *dn, dmu_tx_t *tx, const void *tag)
 {
 	/*
 	 * Don't set dirtyctx to SYNC if we're just modifying this as we
diff --git a/module/zfs/dsl_bookmark.c b/module/zfs/dsl_bookmark.c
index 5d9b674f9..4e44b167f 100644
--- a/module/zfs/dsl_bookmark.c
+++ b/module/zfs/dsl_bookmark.c
@@ -1291,7 +1291,7 @@ dsl_bookmark_ds_destroyed(dsl_dataset_t *ds, dmu_tx_t *tx)
 	 * The empty-string name can't be in the AVL, and it compares
 	 * before any entries with this TXG.
 	 */
-	search.dbn_name = "";
+	search.dbn_name = (char *)"";
 	VERIFY3P(avl_find(&head->ds_bookmarks, &search, &idx), ==, NULL);
 	dsl_bookmark_node_t *dbn =
 	    avl_nearest(&head->ds_bookmarks, idx, AVL_AFTER);
@@ -1418,7 +1418,7 @@ dsl_bookmark_next_changed(dsl_dataset_t *head, dsl_dataset_t *origin,
 	 * The empty-string name can't be in the AVL, and it compares
 	 * before any entries with this TXG.
 	 */
-	search.dbn_name = "";
+	search.dbn_name = (char *)"";
 	VERIFY3P(avl_find(&head->ds_bookmarks, &search, &idx), ==, NULL);
 	dsl_bookmark_node_t *dbn =
 	    avl_nearest(&head->ds_bookmarks, idx, AVL_AFTER);
diff --git a/module/zfs/dsl_crypt.c b/module/zfs/dsl_crypt.c
index d802eb6b6..44e0083d2 100644
--- a/module/zfs/dsl_crypt.c
+++ b/module/zfs/dsl_crypt.c
@@ -1506,7 +1506,7 @@ spa_keystore_change_key_sync(void *arg, dmu_tx_t *tx)
 	dsl_crypto_params_t *dcp = skcka->skcka_cp;
 	dsl_wrapping_key_t *wkey = NULL, *found_wkey;
 	dsl_wrapping_key_t wkey_search;
-	char *keylocation = dcp->cp_keylocation;
+	const char *keylocation = dcp->cp_keylocation;
 	uint64_t rddobj, new_rddobj;
 
 	/* create and initialize the wrapping key */
@@ -2229,7 +2229,7 @@ dsl_crypto_recv_raw_key_sync(dsl_dataset_t *ds, nvlist_t *nvl, dmu_tx_t *tx)
 	uint8_t *keydata, *hmac_keydata, *iv, *mac;
 	uint64_t crypt, key_guid, keyformat, iters, salt;
 	uint64_t version = ZIO_CRYPT_KEY_CURRENT_VERSION;
-	char *keylocation = "prompt";
+	const char *keylocation = "prompt";
 
 	/* lookup the values we need to create the DSL Crypto Key */
 	crypt = fnvlist_lookup_uint64(nvl, DSL_CRYPTO_KEY_CRYPTO_SUITE);
diff --git a/module/zfs/dsl_dataset.c b/module/zfs/dsl_dataset.c
index 805bae12d..106721894 100644
--- a/module/zfs/dsl_dataset.c
+++ b/module/zfs/dsl_dataset.c
@@ -551,7 +551,7 @@ dsl_dataset_snap_remove(dsl_dataset_t *ds, const char *name, dmu_tx_t *tx,
 }
 
 boolean_t
-dsl_dataset_try_add_ref(dsl_pool_t *dp, dsl_dataset_t *ds, void *tag)
+dsl_dataset_try_add_ref(dsl_pool_t *dp, dsl_dataset_t *ds, const void *tag)
 {
 	dmu_buf_t *dbuf = ds->ds_dbuf;
 	boolean_t result = B_FALSE;
@@ -569,7 +569,7 @@ dsl_dataset_try_add_ref(dsl_pool_t *dp, dsl_dataset_t *ds, void *tag)
 }
 
 int
-dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
+dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, const void *tag,
     dsl_dataset_t **dsp)
 {
 	objset_t *mos = dp->dp_meta_objset;
@@ -758,7 +758,7 @@ dsl_dataset_create_key_mapping(dsl_dataset_t *ds)
 
 int
 dsl_dataset_hold_obj_flags(dsl_pool_t *dp, uint64_t dsobj,
-    ds_hold_flags_t flags, void *tag, dsl_dataset_t **dsp)
+    ds_hold_flags_t flags, const void *tag, dsl_dataset_t **dsp)
 {
 	int err;
 
@@ -779,7 +779,7 @@ dsl_dataset_hold_obj_flags(dsl_pool_t *dp, uint64_t dsobj,
 
 int
 dsl_dataset_hold_flags(dsl_pool_t *dp, const char *name, ds_hold_flags_t flags,
-    void *tag, dsl_dataset_t **dsp)
+    const void *tag, dsl_dataset_t **dsp)
 {
 	dsl_dir_t *dd;
 	const char *snapname;
@@ -832,7 +832,7 @@ dsl_dataset_hold_flags(dsl_pool_t *dp, const char *name, ds_hold_flags_t flags,
 }
 
 int
-dsl_dataset_hold(dsl_pool_t *dp, const char *name, void *tag,
+dsl_dataset_hold(dsl_pool_t *dp, const char *name, const void *tag,
     dsl_dataset_t **dsp)
 {
 	return (dsl_dataset_hold_flags(dp, name, 0, tag, dsp));
@@ -840,7 +840,7 @@ dsl_dataset_hold(dsl_pool_t *dp, const char *name, void *tag,
 
 static int
 dsl_dataset_own_obj_impl(dsl_pool_t *dp, uint64_t dsobj, ds_hold_flags_t flags,
-    void *tag, boolean_t override, dsl_dataset_t **dsp)
+    const void *tag, boolean_t override, dsl_dataset_t **dsp)
 {
 	int err = dsl_dataset_hold_obj_flags(dp, dsobj, flags, tag, dsp);
 	if (err != 0)
@@ -856,21 +856,21 @@ dsl_dataset_own_obj_impl(dsl_pool_t *dp, uint64_t dsobj, ds_hold_flags_t flags,
 
 int
 dsl_dataset_own_obj(dsl_pool_t *dp, uint64_t dsobj, ds_hold_flags_t flags,
-    void *tag, dsl_dataset_t **dsp)
+    const void *tag, dsl_dataset_t **dsp)
 {
 	return (dsl_dataset_own_obj_impl(dp, dsobj, flags, tag, B_FALSE, dsp));
 }
 
 int
 dsl_dataset_own_obj_force(dsl_pool_t *dp, uint64_t dsobj,
-    ds_hold_flags_t flags, void *tag, dsl_dataset_t **dsp)
+    ds_hold_flags_t flags, const void *tag, dsl_dataset_t **dsp)
 {
 	return (dsl_dataset_own_obj_impl(dp, dsobj, flags, tag, B_TRUE, dsp));
 }
 
 static int
 dsl_dataset_own_impl(dsl_pool_t *dp, const char *name, ds_hold_flags_t flags,
-    void *tag, boolean_t override, dsl_dataset_t **dsp)
+    const void *tag, boolean_t override, dsl_dataset_t **dsp)
 {
 	int err = dsl_dataset_hold_flags(dp, name, flags, tag, dsp);
 	if (err != 0)
@@ -884,14 +884,14 @@ dsl_dataset_own_impl(dsl_pool_t *dp, const char *name, ds_hold_flags_t flags,
 
 int
 dsl_dataset_own_force(dsl_pool_t *dp, const char *name, ds_hold_flags_t flags,
-    void *tag, dsl_dataset_t **dsp)
+    const void *tag, dsl_dataset_t **dsp)
 {
 	return (dsl_dataset_own_impl(dp, name, flags, tag, B_TRUE, dsp));
 }
 
 int
 dsl_dataset_own(dsl_pool_t *dp, const char *name, ds_hold_flags_t flags,
-    void *tag, dsl_dataset_t **dsp)
+    const void *tag, dsl_dataset_t **dsp)
 {
 	return (dsl_dataset_own_impl(dp, name, flags, tag, B_FALSE, dsp));
 }
@@ -970,7 +970,7 @@ dsl_dataset_namelen(dsl_dataset_t *ds)
 }
 
 void
-dsl_dataset_rele(dsl_dataset_t *ds, void *tag)
+dsl_dataset_rele(dsl_dataset_t *ds, const void *tag)
 {
 	dmu_buf_rele(ds->ds_dbuf, tag);
 }
@@ -988,7 +988,8 @@ dsl_dataset_remove_key_mapping(dsl_dataset_t *ds)
 }
 
 void
-dsl_dataset_rele_flags(dsl_dataset_t *ds, ds_hold_flags_t flags, void *tag)
+dsl_dataset_rele_flags(dsl_dataset_t *ds, ds_hold_flags_t flags,
+    const void *tag)
 {
 	if (flags & DS_HOLD_FLAG_DECRYPT)
 		dsl_dataset_remove_key_mapping(ds);
@@ -997,7 +998,7 @@ dsl_dataset_rele_flags(dsl_dataset_t *ds, ds_hold_flags_t flags, void *tag)
 }
 
 void
-dsl_dataset_disown(dsl_dataset_t *ds, ds_hold_flags_t flags, void *tag)
+dsl_dataset_disown(dsl_dataset_t *ds, ds_hold_flags_t flags, const void *tag)
 {
 	ASSERT3P(ds->ds_owner, ==, tag);
 	ASSERT(ds->ds_dbuf != NULL);
@@ -1010,7 +1011,7 @@ dsl_dataset_disown(dsl_dataset_t *ds, ds_hold_flags_t flags, void *tag)
 }
 
 boolean_t
-dsl_dataset_tryown(dsl_dataset_t *ds, void *tag, boolean_t override)
+dsl_dataset_tryown(dsl_dataset_t *ds, const void *tag, boolean_t override)
 {
 	boolean_t gotit = FALSE;
 
@@ -3278,8 +3279,8 @@ struct promotenode {
 
 static int snaplist_space(list_t *l, uint64_t mintxg, uint64_t *spacep);
 static int promote_hold(dsl_dataset_promote_arg_t *ddpa, dsl_pool_t *dp,
-    void *tag);
-static void promote_rele(dsl_dataset_promote_arg_t *ddpa, void *tag);
+    const void *tag);
+static void promote_rele(dsl_dataset_promote_arg_t *ddpa, const void *tag);
 
 int
 dsl_dataset_promote_check(void *arg, dmu_tx_t *tx)
@@ -3739,7 +3740,7 @@ dsl_dataset_promote_sync(void *arg, dmu_tx_t *tx)
  */
 static int
 snaplist_make(dsl_pool_t *dp,
-    uint64_t first_obj, uint64_t last_obj, list_t *l, void *tag)
+    uint64_t first_obj, uint64_t last_obj, list_t *l, const void *tag)
 {
 	uint64_t obj = last_obj;
 
@@ -3784,7 +3785,7 @@ snaplist_space(list_t *l, uint64_t mintxg, uint64_t *spacep)
 }
 
 static void
-snaplist_destroy(list_t *l, void *tag)
+snaplist_destroy(list_t *l, const void *tag)
 {
 	struct promotenode *snap;
 
@@ -3800,7 +3801,7 @@ snaplist_destroy(list_t *l, void *tag)
 }
 
 static int
-promote_hold(dsl_dataset_promote_arg_t *ddpa, dsl_pool_t *dp, void *tag)
+promote_hold(dsl_dataset_promote_arg_t *ddpa, dsl_pool_t *dp, const void *tag)
 {
 	int error;
 	dsl_dir_t *dd;
@@ -3850,7 +3851,7 @@ out:
 }
 
 static void
-promote_rele(dsl_dataset_promote_arg_t *ddpa, void *tag)
+promote_rele(dsl_dataset_promote_arg_t *ddpa, const void *tag)
 {
 	snaplist_destroy(&ddpa->shared_snaps, tag);
 	snaplist_destroy(&ddpa->clone_snaps, tag);
diff --git a/module/zfs/dsl_dir.c b/module/zfs/dsl_dir.c
index aca32ff9b..252dd2912 100644
--- a/module/zfs/dsl_dir.c
+++ b/module/zfs/dsl_dir.c
@@ -801,7 +801,7 @@ dsl_fs_ss_limit_check(dsl_dir_t *dd, uint64_t delta, zfs_prop_t prop,
 {
 	objset_t *os = dd->dd_pool->dp_meta_objset;
 	uint64_t limit, count;
-	char *count_prop;
+	const char *count_prop;
 	enforce_res_t enforce;
 	int err = 0;
 
diff --git a/module/zfs/dsl_pool.c b/module/zfs/dsl_pool.c
index 4a6d4b623..3c2fefcfb 100644
--- a/module/zfs/dsl_pool.c
+++ b/module/zfs/dsl_pool.c
@@ -1387,7 +1387,7 @@ dsl_pool_user_release(dsl_pool_t *dp, uint64_t dsobj, const char *tag,
  */
 
 int
-dsl_pool_hold(const char *name, void *tag, dsl_pool_t **dp)
+dsl_pool_hold(const char *name, const void *tag, dsl_pool_t **dp)
 {
 	spa_t *spa;
 	int error;
@@ -1401,14 +1401,14 @@ dsl_pool_hold(const char *name, void *tag, dsl_pool_t **dp)
 }
 
 void
-dsl_pool_rele(dsl_pool_t *dp, void *tag)
+dsl_pool_rele(dsl_pool_t *dp, const void *tag)
 {
 	dsl_pool_config_exit(dp, tag);
 	spa_close(dp->dp_spa, tag);
 }
 
 void
-dsl_pool_config_enter(dsl_pool_t *dp, void *tag)
+dsl_pool_config_enter(dsl_pool_t *dp, const void *tag)
 {
 	/*
 	 * We use a "reentrant" reader-writer lock, but not reentrantly.
@@ -1427,14 +1427,14 @@ dsl_pool_config_enter(dsl_pool_t *dp, void *tag)
 }
 
 void
-dsl_pool_config_enter_prio(dsl_pool_t *dp, void *tag)
+dsl_pool_config_enter_prio(dsl_pool_t *dp, const void *tag)
 {
 	ASSERT(!rrw_held(&dp->dp_config_rwlock, RW_READER));
 	rrw_enter_read_prio(&dp->dp_config_rwlock, tag);
 }
 
 void
-dsl_pool_config_exit(dsl_pool_t *dp, void *tag)
+dsl_pool_config_exit(dsl_pool_t *dp, const void *tag)
 {
 	rrw_exit(&dp->dp_config_rwlock, tag);
 }
diff --git a/module/zfs/dsl_userhold.c b/module/zfs/dsl_userhold.c
index 75d153194..499ab09ec 100644
--- a/module/zfs/dsl_userhold.c
+++ b/module/zfs/dsl_userhold.c
@@ -346,7 +346,7 @@ dsl_dataset_user_hold(nvlist_t *holds, minor_t cleanup_minor, nvlist_t *errlist)
 	return (ret);
 }
 
-typedef int (dsl_holdfunc_t)(dsl_pool_t *dp, const char *name, void *tag,
+typedef int (dsl_holdfunc_t)(dsl_pool_t *dp, const char *name, const void *tag,
     dsl_dataset_t **dsp);
 
 typedef struct dsl_dataset_user_release_arg {
@@ -359,7 +359,7 @@ typedef struct dsl_dataset_user_release_arg {
 
 /* Place a dataset hold on the snapshot identified by passed dsobj string */
 static int
-dsl_dataset_hold_obj_string(dsl_pool_t *dp, const char *dsobj, void *tag,
+dsl_dataset_hold_obj_string(dsl_pool_t *dp, const char *dsobj, const void *tag,
     dsl_dataset_t **dsp)
 {
 	return (dsl_dataset_hold_obj(dp, zfs_strtonum(dsobj, NULL), tag, dsp));
diff --git a/module/zfs/mmp.c b/module/zfs/mmp.c
index b03b90fdc..ab0f055ff 100644
--- a/module/zfs/mmp.c
+++ b/module/zfs/mmp.c
@@ -186,7 +186,7 @@ uint_t zfs_multihost_import_intervals = MMP_DEFAULT_IMPORT_INTERVALS;
  */
 uint_t zfs_multihost_fail_intervals = MMP_DEFAULT_FAIL_INTERVALS;
 
-static void *const mmp_tag = "mmp_write_uberblock";
+static const void *const mmp_tag = "mmp_write_uberblock";
 static __attribute__((noreturn)) void mmp_thread(void *arg);
 
 void
diff --git a/module/zfs/rrwlock.c b/module/zfs/rrwlock.c
index d23fc3ad1..8e3ee5ddf 100644
--- a/module/zfs/rrwlock.c
+++ b/module/zfs/rrwlock.c
@@ -77,7 +77,7 @@ uint_t rrw_tsd_key;
 typedef struct rrw_node {
 	struct rrw_node *rn_next;
 	rrwlock_t *rn_rrl;
-	void *rn_tag;
+	const void *rn_tag;
 } rrw_node_t;
 
 static rrw_node_t *
@@ -99,7 +99,7 @@ rrn_find(rrwlock_t *rrl)
  * Add a node to the head of the singly linked list.
  */
 static void
-rrn_add(rrwlock_t *rrl, void *tag)
+rrn_add(rrwlock_t *rrl, const void *tag)
 {
 	rrw_node_t *rn;
 
@@ -115,7 +115,7 @@ rrn_add(rrwlock_t *rrl, void *tag)
  * thread's list and return TRUE; otherwise return FALSE.
  */
 static boolean_t
-rrn_find_and_remove(rrwlock_t *rrl, void *tag)
+rrn_find_and_remove(rrwlock_t *rrl, const void *tag)
 {
 	rrw_node_t *rn;
 	rrw_node_t *prev = NULL;
@@ -160,7 +160,7 @@ rrw_destroy(rrwlock_t *rrl)
 }
 
 static void
-rrw_enter_read_impl(rrwlock_t *rrl, boolean_t prio, void *tag)
+rrw_enter_read_impl(rrwlock_t *rrl, boolean_t prio, const void *tag)
 {
 	mutex_enter(&rrl->rr_lock);
 #if !defined(ZFS_DEBUG) && defined(_KERNEL)
@@ -192,7 +192,7 @@ rrw_enter_read_impl(rrwlock_t *rrl, boolean_t prio, void *tag)
 }
 
 void
-rrw_enter_read(rrwlock_t *rrl, void *tag)
+rrw_enter_read(rrwlock_t *rrl, const void *tag)
 {
 	rrw_enter_read_impl(rrl, B_FALSE, tag);
 }
@@ -204,7 +204,7 @@ rrw_enter_read(rrwlock_t *rrl, void *tag)
  * the pending writer does not work, so we have to give an explicit hint here.
  */
 void
-rrw_enter_read_prio(rrwlock_t *rrl, void *tag)
+rrw_enter_read_prio(rrwlock_t *rrl, const void *tag)
 {
 	rrw_enter_read_impl(rrl, B_TRUE, tag);
 }
@@ -228,7 +228,7 @@ rrw_enter_write(rrwlock_t *rrl)
 }
 
 void
-rrw_enter(rrwlock_t *rrl, krw_t rw, void *tag)
+rrw_enter(rrwlock_t *rrl, krw_t rw, const void *tag)
 {
 	if (rw == RW_READER)
 		rrw_enter_read(rrl, tag);
@@ -237,7 +237,7 @@ rrw_enter(rrwlock_t *rrl, krw_t rw, void *tag)
 }
 
 void
-rrw_exit(rrwlock_t *rrl, void *tag)
+rrw_exit(rrwlock_t *rrl, const void *tag)
 {
 	mutex_enter(&rrl->rr_lock);
 #if !defined(ZFS_DEBUG) && defined(_KERNEL)
@@ -339,7 +339,7 @@ rrm_destroy(rrmlock_t *rrl)
 }
 
 void
-rrm_enter(rrmlock_t *rrl, krw_t rw, void *tag)
+rrm_enter(rrmlock_t *rrl, krw_t rw, const void *tag)
 {
 	if (rw == RW_READER)
 		rrm_enter_read(rrl, tag);
@@ -358,7 +358,7 @@ rrm_enter(rrmlock_t *rrl, krw_t rw, void *tag)
 #define	RRM_TD_LOCK()	(((uint32_t)(uintptr_t)(curthread)) % RRM_NUM_LOCKS)
 
 void
-rrm_enter_read(rrmlock_t *rrl, void *tag)
+rrm_enter_read(rrmlock_t *rrl, const void *tag)
 {
 	rrw_enter_read(&rrl->locks[RRM_TD_LOCK()], tag);
 }
@@ -373,7 +373,7 @@ rrm_enter_write(rrmlock_t *rrl)
 }
 
 void
-rrm_exit(rrmlock_t *rrl, void *tag)
+rrm_exit(rrmlock_t *rrl, const void *tag)
 {
 	int i;
 
diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index baa5fc247..55f3a4de6 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -164,7 +164,8 @@ static const zio_taskq_info_t zio_taskqs[ZIO_TYPES][ZIO_TASKQ_TYPES] = {
 static void spa_sync_version(void *arg, dmu_tx_t *tx);
 static void spa_sync_props(void *arg, dmu_tx_t *tx);
 static boolean_t spa_has_active_shared_spare(spa_t *spa);
-static int spa_load_impl(spa_t *spa, spa_import_type_t type, char **ereport);
+static int spa_load_impl(spa_t *spa, spa_import_type_t type,
+    const char **ereport);
 static void spa_vdev_resilver_done(spa_t *spa);
 
 static uint_t	zio_taskq_batch_pct = 80;	  /* 1 thread per cpu in pset */
@@ -277,7 +278,7 @@ static int zfs_livelist_condense_new_alloc = 0;
  * Add a (source=src, propname=propval) list to an nvlist.
  */
 static void
-spa_prop_add_list(nvlist_t *nvl, zpool_prop_t prop, char *strval,
+spa_prop_add_list(nvlist_t *nvl, zpool_prop_t prop, const char *strval,
     uint64_t intval, zprop_source_t src)
 {
 	const char *propname = zpool_prop_to_name(prop);
@@ -2974,7 +2975,7 @@ spa_try_repair(spa_t *spa, nvlist_t *config)
 static int
 spa_load(spa_t *spa, spa_load_state_t state, spa_import_type_t type)
 {
-	char *ereport = FM_EREPORT_ZFS_POOL;
+	const char *ereport = FM_EREPORT_ZFS_POOL;
 	int error;
 
 	spa->spa_load_state = state;
@@ -3291,7 +3292,7 @@ out:
 	 * ZPOOL_CONFIG_MMP_HOSTID   - hostid from the active pool
 	 */
 	if (error == EREMOTEIO) {
-		char *hostname = "<unknown>";
+		const char *hostname = "<unknown>";
 		uint64_t hostid = 0;
 
 		if (mmp_label) {
@@ -4399,7 +4400,7 @@ spa_ld_load_dedup_tables(spa_t *spa)
 }
 
 static int
-spa_ld_verify_logs(spa_t *spa, spa_import_type_t type, char **ereport)
+spa_ld_verify_logs(spa_t *spa, spa_import_type_t type, const char **ereport)
 {
 	vdev_t *rvd = spa->spa_root_vdev;
 
@@ -4766,7 +4767,7 @@ spa_ld_mos_with_trusted_config(spa_t *spa, spa_import_type_t type,
  * config stored in the MOS.
  */
 static int
-spa_load_impl(spa_t *spa, spa_import_type_t type, char **ereport)
+spa_load_impl(spa_t *spa, spa_import_type_t type, const char **ereport)
 {
 	int error = 0;
 	boolean_t missing_feat_write = B_FALSE;
@@ -5157,8 +5158,8 @@ spa_load_best(spa_t *spa, spa_load_state_t state, uint64_t max_request,
  * ambiguous state.
  */
 static int
-spa_open_common(const char *pool, spa_t **spapp, void *tag, nvlist_t *nvpolicy,
-    nvlist_t **config)
+spa_open_common(const char *pool, spa_t **spapp, const void *tag,
+    nvlist_t *nvpolicy, nvlist_t **config)
 {
 	spa_t *spa;
 	spa_load_state_t state = SPA_LOAD_OPEN;
@@ -5274,14 +5275,14 @@ spa_open_common(const char *pool, spa_t **spapp, void *tag, nvlist_t *nvpolicy,
 }
 
 int
-spa_open_rewind(const char *name, spa_t **spapp, void *tag, nvlist_t *policy,
-    nvlist_t **config)
+spa_open_rewind(const char *name, spa_t **spapp, const void *tag,
+    nvlist_t *policy, nvlist_t **config)
 {
 	return (spa_open_common(name, spapp, tag, policy, config));
 }
 
 int
-spa_open(const char *name, spa_t **spapp, void *tag)
+spa_open(const char *name, spa_t **spapp, const void *tag)
 {
 	return (spa_open_common(name, spapp, tag, NULL, NULL));
 }
@@ -7507,7 +7508,7 @@ spa_vdev_trim(spa_t *spa, nvlist_t *nv, uint64_t cmd_type, uint64_t rate,
  * Split a set of devices from their mirrors, and create a new pool from them.
  */
 int
-spa_vdev_split_mirror(spa_t *spa, char *newname, nvlist_t *config,
+spa_vdev_split_mirror(spa_t *spa, const char *newname, nvlist_t *config,
     nvlist_t *props, boolean_t exp)
 {
 	int error = 0;
diff --git a/module/zfs/spa_config.c b/module/zfs/spa_config.c
index 254031f31..4dcb9f153 100644
--- a/module/zfs/spa_config.c
+++ b/module/zfs/spa_config.c
@@ -67,7 +67,7 @@ static uint64_t spa_config_generation = 1;
  * This can be overridden in userland to preserve an alternate namespace for
  * userland pools when doing testing.
  */
-char *spa_config_path = ZPOOL_CACHE;
+char *spa_config_path = (char *)ZPOOL_CACHE;
 #ifdef _KERNEL
 static int zfs_autoimport_disable = B_TRUE;
 #endif
diff --git a/module/zfs/spa_errlog.c b/module/zfs/spa_errlog.c
index 9e5d1de63..19a3cc814 100644
--- a/module/zfs/spa_errlog.c
+++ b/module/zfs/spa_errlog.c
@@ -659,9 +659,9 @@ sync_upgrade_errlog(spa_t *spa, uint64_t spa_err_obj, uint64_t *newobj,
 		}
 
 		char buf[64];
-		char *name = "";
 		errphys_to_name(&zep, buf, sizeof (buf));
 
+		const char *name = "";
 		(void) zap_update(spa->spa_meta_objset, err_obj,
 		    buf, 1, strlen(name) + 1, name, tx);
 	}
@@ -901,17 +901,14 @@ sync_error_list(spa_t *spa, avl_tree_t *t, uint64_t *obj, dmu_tx_t *tx)
 	/* add errors to the current log */
 	if (!spa_feature_is_enabled(spa, SPA_FEATURE_HEAD_ERRLOG)) {
 		for (se = avl_first(t); se != NULL; se = AVL_NEXT(t, se)) {
-			char *name = se->se_name ? se->se_name : "";
-
 			bookmark_to_name(&se->se_bookmark, buf, sizeof (buf));
 
+			const char *name = se->se_name ? se->se_name : "";
 			(void) zap_update(spa->spa_meta_objset, *obj, buf, 1,
 			    strlen(name) + 1, name, tx);
 		}
 	} else {
 		for (se = avl_first(t); se != NULL; se = AVL_NEXT(t, se)) {
-			char *name = se->se_name ? se->se_name : "";
-
 			zbookmark_err_phys_t zep;
 			zep.zb_object = se->se_bookmark.zb_object;
 			zep.zb_level = se->se_bookmark.zb_level;
@@ -943,6 +940,7 @@ sync_error_list(spa_t *spa, avl_tree_t *t, uint64_t *obj, dmu_tx_t *tx)
 			}
 			errphys_to_name(&zep, buf, sizeof (buf));
 
+			const char *name = se->se_name ? se->se_name : "";
 			(void) zap_update(spa->spa_meta_objset,
 			    err_obj, buf, 1, strlen(name) + 1, name, tx);
 		}
@@ -1153,7 +1151,7 @@ swap_errlog(spa_t *spa, uint64_t spa_err_obj, uint64_t new_head, uint64_t
 	for (zap_cursor_init(&zc, spa->spa_meta_objset, old_head_errlog);
 	    zap_cursor_retrieve(&zc, &za) == 0; zap_cursor_advance(&zc)) {
 
-		char *name = "";
+		const char *name = "";
 		name_to_errphys(za.za_name, &err_block);
 		if (err_block.zb_birth < txg) {
 			(void) zap_update(spa->spa_meta_objset, new_head_errlog,
diff --git a/module/zfs/spa_misc.c b/module/zfs/spa_misc.c
index c57c69bd7..aaca2a8a5 100644
--- a/module/zfs/spa_misc.c
+++ b/module/zfs/spa_misc.c
@@ -462,7 +462,7 @@ spa_config_lock_destroy(spa_t *spa)
 }
 
 int
-spa_config_tryenter(spa_t *spa, int locks, void *tag, krw_t rw)
+spa_config_tryenter(spa_t *spa, int locks, const void *tag, krw_t rw)
 {
 	for (int i = 0; i < SCL_LOCKS; i++) {
 		spa_config_lock_t *scl = &spa->spa_config_lock[i];
@@ -877,7 +877,7 @@ spa_next(spa_t *prev)
  * have the namespace lock held.
  */
 void
-spa_open_ref(spa_t *spa, void *tag)
+spa_open_ref(spa_t *spa, const void *tag)
 {
 	ASSERT(zfs_refcount_count(&spa->spa_refcount) >= spa->spa_minref ||
 	    MUTEX_HELD(&spa_namespace_lock));
@@ -889,7 +889,7 @@ spa_open_ref(spa_t *spa, void *tag)
  * have the namespace lock held.
  */
 void
-spa_close(spa_t *spa, void *tag)
+spa_close(spa_t *spa, const void *tag)
 {
 	ASSERT(zfs_refcount_count(&spa->spa_refcount) > spa->spa_minref ||
 	    MUTEX_HELD(&spa_namespace_lock));
@@ -905,7 +905,7 @@ spa_close(spa_t *spa, void *tag)
  * so the asserts in spa_close() do not apply.
  */
 void
-spa_async_close(spa_t *spa, void *tag)
+spa_async_close(spa_t *spa, const void *tag)
 {
 	(void) zfs_refcount_remove(&spa->spa_refcount, tag);
 }
@@ -1513,8 +1513,8 @@ void
 snprintf_blkptr(char *buf, size_t buflen, const blkptr_t *bp)
 {
 	char type[256];
-	char *checksum = NULL;
-	char *compress = NULL;
+	const char *checksum = NULL;
+	const char *compress = NULL;
 
 	if (bp != NULL) {
 		if (BP_GET_TYPE(bp) & DMU_OT_NEWTYPE) {
diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index 2dcb97b7f..dedbc1a23 100644
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -5790,7 +5790,7 @@ vdev_prop_get(vdev_t *vd, nvlist_t *innvl, nvlist_t *outnvl)
 					    KM_SLEEP);
 				for (uint64_t i = 0; i < vd->vdev_children;
 				    i++) {
-					char *vname;
+					const char *vname;
 
 					vname = vdev_name(vd->vdev_child[i],
 					    namebuf, sizeof (namebuf));
diff --git a/module/zfs/vdev_raidz_math.c b/module/zfs/vdev_raidz_math.c
index 50b8dab74..c58895973 100644
--- a/module/zfs/vdev_raidz_math.c
+++ b/module/zfs/vdev_raidz_math.c
@@ -563,7 +563,7 @@ vdev_raidz_math_fini(void)
 }
 
 static const struct {
-	char *name;
+	const char *name;
 	uint32_t sel;
 } math_impl_opts[] = {
 		{ "cycle",	IMPL_CYCLE },
diff --git a/module/zfs/vdev_rebuild.c b/module/zfs/vdev_rebuild.c
index a965912ac..aa7ed24de 100644
--- a/module/zfs/vdev_rebuild.c
+++ b/module/zfs/vdev_rebuild.c
@@ -260,7 +260,7 @@ vdev_rebuild_initiate_sync(void *arg, dmu_tx_t *tx)
 }
 
 static void
-vdev_rebuild_log_notify(spa_t *spa, vdev_t *vd, char *name)
+vdev_rebuild_log_notify(spa_t *spa, vdev_t *vd, const char *name)
 {
 	nvlist_t *aux = fnvlist_alloc();
 
diff --git a/module/zfs/vdev_removal.c b/module/zfs/vdev_removal.c
index 7dfc4345f..7fbe38b42 100644
--- a/module/zfs/vdev_removal.c
+++ b/module/zfs/vdev_removal.c
@@ -338,8 +338,8 @@ spa_vdev_alloc(spa_t *spa, uint64_t guid)
 }
 
 static void
-spa_vdev_remove_aux(nvlist_t *config, char *name, nvlist_t **dev, int count,
-    nvlist_t *dev_to_remove)
+spa_vdev_remove_aux(nvlist_t *config, const char *name, nvlist_t **dev,
+    int count, nvlist_t *dev_to_remove)
 {
 	nvlist_t **newdev = NULL;
 
@@ -2384,7 +2384,8 @@ spa_vdev_remove(spa_t *spa, uint64_t guid, boolean_t unspare)
 	int error = 0, error_log;
 	boolean_t locked = MUTEX_HELD(&spa_namespace_lock);
 	sysevent_t *ev = NULL;
-	char *vd_type = NULL, *vd_path = NULL;
+	const char *vd_type = NULL;
+	char *vd_path = NULL;
 
 	ASSERT(spa_writeable(spa));
 
diff --git a/module/zfs/zfs_fuid.c b/module/zfs/zfs_fuid.c
index 3aa60034d..976333ee8 100644
--- a/module/zfs/zfs_fuid.c
+++ b/module/zfs/zfs_fuid.c
@@ -61,7 +61,7 @@ typedef struct fuid_domain {
 	uint64_t	f_idx;
 } fuid_domain_t;
 
-static char *nulldomain = "";
+static const char *const nulldomain = "";
 
 /*
  * Compare two indexes.
@@ -171,7 +171,7 @@ zfs_fuid_table_destroy(avl_tree_t *idx_tree, avl_tree_t *domain_tree)
 	avl_destroy(idx_tree);
 }
 
-char *
+const char *
 zfs_fuid_idx_domain(avl_tree_t *idx_tree, uint32_t idx)
 {
 	fuid_domain_t searchnode, *findnode;
@@ -290,9 +290,9 @@ zfs_fuid_sync(zfsvfs_t *zfsvfs, dmu_tx_t *tx)
  * necessary for the caller or another thread to detect the dirty table
  * and sync out the changes.
  */
-int
+static int
 zfs_fuid_find_by_domain(zfsvfs_t *zfsvfs, const char *domain,
-    char **retdomain, boolean_t addok)
+    const char **retdomain, boolean_t addok)
 {
 	fuid_domain_t searchnode, *findnode;
 	avl_index_t loc;
@@ -358,7 +358,7 @@ retry:
 const char *
 zfs_fuid_find_by_idx(zfsvfs_t *zfsvfs, uint32_t idx)
 {
-	char *domain;
+	const char *domain;
 
 	if (idx == 0 || !zfsvfs->z_use_fuids)
 		return (NULL);
@@ -518,8 +518,7 @@ zfs_fuid_create_cred(zfsvfs_t *zfsvfs, zfs_fuid_type_t type,
 	uint64_t	idx;
 	ksid_t		*ksid;
 	uint32_t	rid;
-	char		*kdomain;
-	const char	*domain;
+	const char	*kdomain, *domain;
 	uid_t		id;
 
 	VERIFY(type == ZFS_OWNER || type == ZFS_GROUP);
@@ -574,8 +573,7 @@ zfs_fuid_create(zfsvfs_t *zfsvfs, uint64_t id, cred_t *cr,
     zfs_fuid_type_t type, zfs_fuid_info_t **fuidpp)
 {
 #ifdef HAVE_KSID
-	const char *domain;
-	char *kdomain;
+	const char *domain, *kdomain;
 	uint32_t fuid_idx = FUID_INDEX(id);
 	uint32_t rid = 0;
 	idmap_stat status;
diff --git a/module/zfs/zil.c b/module/zfs/zil.c
index 9adf81551..9de60896d 100644
--- a/module/zfs/zil.c
+++ b/module/zfs/zil.c
@@ -3470,7 +3470,7 @@ zil_close(zilog_t *zilog)
 	mutex_exit(&zilog->zl_lock);
 }
 
-static char *suspend_tag = "zil suspending";
+static const char *suspend_tag = "zil suspending";
 
 /*
  * Suspend an intent log.  While in suspended mode, we still honor
diff --git a/module/zfs/zio_checksum.c b/module/zfs/zio_checksum.c
index 3c5cdf604..c7368ac26 100644
--- a/module/zfs/zio_checksum.c
+++ b/module/zfs/zio_checksum.c
@@ -160,7 +160,7 @@ abd_fletcher_4_byteswap(abd_t *abd, uint64_t size,
 	abd_fletcher_4_impl(abd, size, &acd);
 }
 
-zio_checksum_info_t zio_checksum_table[ZIO_CHECKSUM_FUNCTIONS] = {
+const zio_checksum_info_t zio_checksum_table[ZIO_CHECKSUM_FUNCTIONS] = {
 	{{NULL, NULL}, NULL, NULL, 0, "inherit"},
 	{{NULL, NULL}, NULL, NULL, 0, "on"},
 	{{abd_checksum_off,		abd_checksum_off},
diff --git a/module/zfs/zio_compress.c b/module/zfs/zio_compress.c
index 38020ce22..717395dcf 100644
--- a/module/zfs/zio_compress.c
+++ b/module/zfs/zio_compress.c
@@ -49,7 +49,7 @@ unsigned long zio_decompress_fail_fraction = 0;
 /*
  * Compression vectors.
  */
-zio_compress_info_t zio_compress_table[ZIO_COMPRESS_FUNCTIONS] = {
+const zio_compress_info_t zio_compress_table[ZIO_COMPRESS_FUNCTIONS] = {
 	{"inherit",	0,	NULL,		NULL, NULL},
 	{"on",		0,	NULL,		NULL, NULL},
 	{"uncompressed", 0,	NULL,		NULL, NULL},
diff --git a/tests/zfs-tests/cmd/ctime.c b/tests/zfs-tests/cmd/ctime.c
index cb2be72ee..6d9cf9608 100644
--- a/tests/zfs-tests/cmd/ctime.c
+++ b/tests/zfs-tests/cmd/ctime.c
@@ -51,7 +51,7 @@
 
 typedef struct timetest {
 	int	type;
-	char	*name;
+	const char	*name;
 	int	(*func)(const char *pfile);
 } timetest_t;
 
@@ -260,7 +260,7 @@ static int
 do_xattr(const char *pfile)
 {
 	int ret = 0;
-	char *value = "user.value";
+	const char *value = "user.value";
 
 	if (pfile == NULL) {
 		return (-1);
@@ -306,7 +306,7 @@ int
 main(void)
 {
 	int i, ret, fd;
-	char *penv[] = {"TESTDIR", "TESTFILE0"};
+	const char *penv[] = {"TESTDIR", "TESTFILE0"};
 
 	(void) atexit(cleanup);
 
diff --git a/tests/zfs-tests/cmd/dir_rd_update.c b/tests/zfs-tests/cmd/dir_rd_update.c
index ea46f047a..0f460fbec 100644
--- a/tests/zfs-tests/cmd/dir_rd_update.c
+++ b/tests/zfs-tests/cmd/dir_rd_update.c
@@ -47,7 +47,7 @@ static char dirpath[256];
 int
 main(int argc, char **argv)
 {
-	char *cp1 = "";
+	const char *cp1 = "";
 	int i = 0;
 	int ret = 0;
 	int testdd = 0;
diff --git a/tests/zfs-tests/cmd/draid.c b/tests/zfs-tests/cmd/draid.c
index 618cb9c4d..d1183b438 100644
--- a/tests/zfs-tests/cmd/draid.c
+++ b/tests/zfs-tests/cmd/draid.c
@@ -130,7 +130,7 @@ read_map(const char *filename, nvlist_t **allcfgs)
  * for freeing the configuration returned.
  */
 static int
-read_map_key(const char *filename, char *key, nvlist_t **cfg)
+read_map_key(const char *filename, const char *key, nvlist_t **cfg)
 {
 	nvlist_t *allcfgs, *foundcfg = NULL;
 	int error;
@@ -320,8 +320,8 @@ write_map_key(const char *filename, char *key, draid_map_t *map,
 }
 
 static void
-dump_map(draid_map_t *map, char *key, double worst_ratio, double avg_ratio,
-    int verbose)
+dump_map(draid_map_t *map, const char *key, double worst_ratio,
+    double avg_ratio, int verbose)
 {
 	if (verbose == 0) {
 		return;
@@ -363,7 +363,7 @@ dump_map(draid_map_t *map, char *key, double worst_ratio, double avg_ratio,
 }
 
 static void
-dump_map_nv(char *key, nvlist_t *cfg, int verbose)
+dump_map_nv(const char *key, nvlist_t *cfg, int verbose)
 {
 	draid_map_t map;
 	uint_t c;
@@ -385,7 +385,7 @@ dump_map_nv(char *key, nvlist_t *cfg, int verbose)
  * Print a summary of the mapping.
  */
 static int
-dump_map_key(const char *filename, char *key, int verbose)
+dump_map_key(const char *filename, const char *key, int verbose)
 {
 	nvlist_t *cfg;
 	int error;
diff --git a/tests/zfs-tests/cmd/get_diff.c b/tests/zfs-tests/cmd/get_diff.c
index 2799f46b0..3f8fe787f 100644
--- a/tests/zfs-tests/cmd/get_diff.c
+++ b/tests/zfs-tests/cmd/get_diff.c
@@ -25,10 +25,9 @@
 #include <errno.h>
 
 static void
-usage(char *msg, int exit_value)
+usage(const char *msg, int exit_value)
 {
-	(void) fprintf(stderr, "get_diff file redacted_file\n");
-	(void) fprintf(stderr, "%s\n", msg);
+	(void) fprintf(stderr, "usage: get_diff file redacted_file\n%s\n", msg);
 	exit(exit_value);
 }
 
diff --git a/tests/zfs-tests/cmd/libzfs_input_check.c b/tests/zfs-tests/cmd/libzfs_input_check.c
index bfa450be5..e84a00273 100644
--- a/tests/zfs-tests/cmd/libzfs_input_check.c
+++ b/tests/zfs-tests/cmd/libzfs_input_check.c
@@ -596,13 +596,13 @@ test_channel_program(const char *pool)
 	    "arg = ...\n"
 	    "argv = arg[\"argv\"]\n"
 	    "return argv[1]";
-	char *const argv[1] = { "Hello World!" };
+	const char *const argv[1] = { "Hello World!" };
 	nvlist_t *required = fnvlist_alloc();
 	nvlist_t *optional = fnvlist_alloc();
 	nvlist_t *args = fnvlist_alloc();
 
 	fnvlist_add_string(required, "program", program);
-	fnvlist_add_string_array(args, "argv", (const char * const *)argv, 1);
+	fnvlist_add_string_array(args, "argv", argv, 1);
 	fnvlist_add_nvlist(required, "arg", args);
 
 	fnvlist_add_boolean_value(optional, "sync", B_TRUE);
diff --git a/tests/zfs-tests/cmd/mkbusy.c b/tests/zfs-tests/cmd/mkbusy.c
index 75b5736e5..cc4a6cfcb 100644
--- a/tests/zfs-tests/cmd/mkbusy.c
+++ b/tests/zfs-tests/cmd/mkbusy.c
@@ -32,14 +32,14 @@
 
 
 static __attribute__((noreturn)) void
-usage(char *progname)
+usage(const char *progname)
 {
 	(void) fprintf(stderr, "Usage: %s <dirname|filename>\n", progname);
 	exit(1);
 }
 
 static __attribute__((noreturn)) void
-fail(char *err)
+fail(const char *err)
 {
 	perror(err);
 	exit(1);
diff --git a/tests/zfs-tests/cmd/mkfiles.c b/tests/zfs-tests/cmd/mkfiles.c
index 32abfd0c3..76be4dadb 100644
--- a/tests/zfs-tests/cmd/mkfiles.c
+++ b/tests/zfs-tests/cmd/mkfiles.c
@@ -21,13 +21,11 @@
 #include <unistd.h>
 #include <sys/param.h>
 
-#define	MAX_INT_LENGTH 10
-
 static void
-usage(char *msg, int exit_value)
+usage(const char *msg, int exit_value)
 {
-	(void) fprintf(stderr, "mkfiles basename max_file [min_file]\n");
-	(void) fprintf(stderr, "%s\n", msg);
+	(void) fprintf(stderr, "usage: mkfiles basename max_file [min_file]\n"
+	    "%s\n", msg);
 	exit(exit_value);
 }
 
@@ -40,13 +38,13 @@ main(int argc, char **argv)
 	char buf[MAXPATHLEN];
 
 	if (argc < 3 || argc > 4)
-		usage("Invalid number of arguments", -1);
+		usage("Invalid number of arguments", 1);
 
 	if (sscanf(argv[2], "%u", &numfiles) != 1)
-		usage("Invalid maximum file", -2);
+		usage("Invalid maximum file", 2);
 
 	if (argc == 4 && sscanf(argv[3], "%u", &first_file) != 1)
-		usage("Invalid first file", -3);
+		usage("Invalid first file", 3);
 
 	for (i = first_file; i < first_file + numfiles; i++) {
 		int fd;
@@ -54,11 +52,11 @@ main(int argc, char **argv)
 		if ((fd = open(buf, O_CREAT | O_EXCL, O_RDWR)) == -1) {
 			(void) fprintf(stderr, "Failed to create %s %s\n", buf,
 			    strerror(errno));
-			return (-4);
+			return (4);
 		} else if (fchown(fd, getuid(), getgid()) < 0) {
 			(void) fprintf(stderr, "Failed to chown %s %s\n", buf,
 			    strerror(errno));
-			return (-5);
+			return (5);
 		}
 		(void) close(fd);
 	}
diff --git a/tests/zfs-tests/cmd/mktree.c b/tests/zfs-tests/cmd/mktree.c
index 25b26c9e1..8ee86e5a0 100644
--- a/tests/zfs-tests/cmd/mktree.c
+++ b/tests/zfs-tests/cmd/mktree.c
@@ -153,7 +153,7 @@ crtfile(char *pname)
 {
 	int fd = -1;
 	int i, size;
-	char *context = "0123456789ABCDF";
+	const char *context = "0123456789ABCDF";
 	char *pbuf;
 
 	if (pname == NULL) {
diff --git a/tests/zfs-tests/cmd/nvlist_to_lua.c b/tests/zfs-tests/cmd/nvlist_to_lua.c
index 4d2abfeb1..b65b3fd26 100644
--- a/tests/zfs-tests/cmd/nvlist_to_lua.c
+++ b/tests/zfs-tests/cmd/nvlist_to_lua.c
@@ -84,7 +84,7 @@ nvlist_equal(nvlist_t *nvla, nvlist_t *nvlb)
 static void
 test(const char *testname, boolean_t expect_success, boolean_t expect_match)
 {
-	char *progstr = "input = ...; return {output=input}";
+	const char *progstr = "input = ...; return {output=input}";
 
 	nvlist_t *outnvl;
 
@@ -230,8 +230,8 @@ run_tests(void)
 		test("uint64_array", B_FALSE, B_FALSE);
 	}
 	{
-		char *const val[2] = { "0", "1" };
-		fnvlist_add_string_array(nvl, key, (const char **)val, 2);
+		const char *val[2] = { "0", "1" };
+		fnvlist_add_string_array(nvl, key, val, 2);
 		test("string_array", B_TRUE, B_FALSE);
 	}
 	{
diff --git a/tests/zfs-tests/cmd/readmmap.c b/tests/zfs-tests/cmd/readmmap.c
index e21c2c867..f119e114d 100644
--- a/tests/zfs-tests/cmd/readmmap.c
+++ b/tests/zfs-tests/cmd/readmmap.c
@@ -49,7 +49,7 @@
 int
 main(int argc, char **argv)
 {
-	char *filename = "badfile";
+	const char *filename = "badfile";
 	size_t size = 4395;
 	size_t idx = 0;
 	char *buf = NULL;
diff --git a/tests/zfs-tests/cmd/stride_dd.c b/tests/zfs-tests/cmd/stride_dd.c
index 88bd53292..732ac9f47 100644
--- a/tests/zfs-tests/cmd/stride_dd.c
+++ b/tests/zfs-tests/cmd/stride_dd.c
@@ -27,7 +27,7 @@ static char *ifile = NULL;
 static char *ofile = NULL;
 static int stride = 0;
 static int seek = 0;
-static char *execname = "stride_dd";
+static const char *execname = "stride_dd";
 
 static void usage(void);
 static void parse_options(int argc, char *argv[]);
diff --git a/tests/zfs-tests/cmd/xattrtest.c b/tests/zfs-tests/cmd/xattrtest.c
index 49b6629ba..4f82facb0 100644
--- a/tests/zfs-tests/cmd/xattrtest.c
+++ b/tests/zfs-tests/cmd/xattrtest.c
@@ -91,8 +91,8 @@ static int size_is_random = 0;
 static int value_is_random = 0;
 static int keep_files = 0;
 static int phase = PHASE_ALL;
-static char path[PATH_MAX] = "/tmp/xattrtest";
-static char script[PATH_MAX] = "/bin/true";
+static const char *path = "/tmp/xattrtest";
+static const char *script = "/bin/true";
 static char xattrbytes[XATTR_SIZE_MAX];
 
 static int
@@ -161,8 +161,7 @@ parse_args(int argc, char **argv)
 			}
 			break;
 		case 'p':
-			strncpy(path, optarg, PATH_MAX);
-			path[PATH_MAX - 1] = '\0';
+			path = optarg;
 			break;
 		case 'c':
 			synccaches = 1;
@@ -171,8 +170,7 @@ parse_args(int argc, char **argv)
 			dropcaches = 1;
 			break;
 		case 't':
-			strncpy(script, optarg, PATH_MAX);
-			script[PATH_MAX - 1] = '\0';
+			script = optarg;
 			break;
 		case 'e':
 			seed = strtol(optarg, NULL, 0);
@@ -291,9 +289,9 @@ run_process(const char *path, char *argv[])
 }
 
 static int
-post_hook(char *phase)
+post_hook(const char *phase)
 {
-	char *argv[3] = { script, phase, (char *)0 };
+	char *argv[3] = { (char *)script, (char *)phase, NULL };
 	int rc;
 
 	if (synccaches)
@@ -517,9 +515,9 @@ getxattrs(void)
 	int i, j, rnd_size, shift, rc = 0;
 	char name[XATTR_NAME_MAX];
 	char *verify_value = NULL;
-	char *verify_string;
+	const char *verify_string;
 	char *value = NULL;
-	char *value_string;
+	const char *value_string;
 	char *file = NULL;
 	struct timeval start, stop;
 	double seconds;
diff --git a/tests/zfs-tests/tests/functional/hkdf/hkdf_test.c b/tests/zfs-tests/tests/functional/hkdf/hkdf_test.c
index 473a9ba9a..24aeb0b22 100644
--- a/tests/zfs-tests/tests/functional/hkdf/hkdf_test.c
+++ b/tests/zfs-tests/tests/functional/hkdf/hkdf_test.c
@@ -29,16 +29,16 @@
  */
 typedef struct hkdf_tv {
 	/* test vector input values */
-	char		*ikm;
+	const char		*ikm;
 	uint_t		ikm_len;
-	char		*salt;
+	const char		*salt;
 	uint_t		salt_len;
-	char		*info;
+	const char		*info;
 	uint_t		info_len;
 	uint_t		okm_len;
 
 	/* expected output */
-	char		*okm;
+	const char		*okm;
 } hkdf_tv_t;
 
 /*
@@ -48,7 +48,7 @@ typedef struct hkdf_tv {
  * The current vectors were taken from:
  * https://www.kullo.net/blog/hkdf-sha-512-test-vectors/
  */
-static hkdf_tv_t test_vectors[] = {
+static const hkdf_tv_t test_vectors[] = {
 	{
 		.ikm =	"\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b"
 			"\x0b\x0b\x0b\x0b\x0b\x0b\x0b\x0b"
@@ -170,7 +170,7 @@ static hkdf_tv_t test_vectors[] = {
 };
 
 static void
-hexdump(char *str, uint8_t *src, uint_t len)
+hexdump(const char *str, uint8_t *src, uint_t len)
 {
 	printf("\t%s\t", str);
 	for (int i = 0; i < len; i++)
@@ -179,7 +179,7 @@ hexdump(char *str, uint8_t *src, uint_t len)
 }
 
 static int
-run_test(int i, hkdf_tv_t *tv)
+run_test(int i, const hkdf_tv_t *tv)
 {
 	int ret;
 	uint8_t good[SHA512_DIGEST_LENGTH];
diff --git a/tests/zfs-tests/tests/functional/tmpfile/tmpfile_001_pos.c b/tests/zfs-tests/tests/functional/tmpfile/tmpfile_001_pos.c
index d40da0d2b..503861656 100644
--- a/tests/zfs-tests/tests/functional/tmpfile/tmpfile_001_pos.c
+++ b/tests/zfs-tests/tests/functional/tmpfile/tmpfile_001_pos.c
@@ -8,6 +8,7 @@
 #include <errno.h>
 #include <string.h>
 #include <time.h>
+#include <err.h>
 
 /* backward compat in case it's not defined */
 #ifndef O_TMPFILE
@@ -33,75 +34,45 @@ fill_random(char *buf, int len)
 {
 	srand(time(NULL));
 	for (int i = 0; i < len; i++)
-		buf[i] = (char)rand();
+		buf[i] = (char)(rand() % 0xFF);
 }
 
 int
 main(void)
 {
-	int i, fd;
-	char buf1[BSZ], buf2[BSZ] = {};
-	char *penv[] = {"TESTDIR"};
+	char buf1[BSZ], buf2[BSZ] = {0};
 
 	(void) fprintf(stdout, "Verify O_TMPFILE is working properly.\n");
 
-	/*
-	 * Get the environment variable values.
-	 */
-	for (i = 0; i < sizeof (penv) / sizeof (char *); i++) {
-		if ((penv[i] = getenv(penv[i])) == NULL) {
-			(void) fprintf(stderr, "getenv(penv[%d])\n", i);
-			exit(1);
-		}
-	}
+	const char *testdir = getenv("TESTDIR");
+	if (testdir == NULL)
+		errx(1, "getenv(\"TESTDIR\")");
 
 	fill_random(buf1, BSZ);
 
-	fd = open(penv[0], O_RDWR|O_TMPFILE, 0666);
-	if (fd < 0) {
-		perror("open");
-		exit(2);
-	}
+	int fd = open(testdir, O_RDWR|O_TMPFILE, 0666);
+	if (fd < 0)
+		err(2, "open(%s)", testdir);
 
-	if (write(fd, buf1, BSZ) < 0) {
-		perror("write");
-		close(fd);
-		exit(3);
-	}
+	if (write(fd, buf1, BSZ) < 0)
+		err(3, "write");
 
-	if (pread(fd, buf2, BSZ, 0) < 0) {
-		perror("pread");
-		close(fd);
-		exit(4);
-	}
+	if (pread(fd, buf2, BSZ, 0) < 0)
+		err(4, "pread");
 
-	if (memcmp(buf1, buf2, BSZ) != 0) {
-		fprintf(stderr, "data corrupted\n");
-		close(fd);
-		exit(5);
-	}
+	if (memcmp(buf1, buf2, BSZ) != 0)
+		errx(5, "data corrupted");
 
 	memset(buf2, 0, BSZ);
 
-	if (fsetxattr(fd, "user.test", buf1, BSZ, 0) < 0) {
-		perror("fsetxattr");
-		close(fd);
-		exit(6);
-	}
+	if (fsetxattr(fd, "user.test", buf1, BSZ, 0) < 0)
+		err(6, "pread");
 
-	if (fgetxattr(fd, "user.test", buf2, BSZ) < 0) {
-		perror("fgetxattr");
-		close(fd);
-		exit(7);
-	}
+	if (fgetxattr(fd, "user.test", buf2, BSZ) < 0)
+		err(7, "fgetxattr");
 
-	if (memcmp(buf1, buf2, BSZ) != 0) {
-		fprintf(stderr, "xattr corrupted\n");
-		close(fd);
-		exit(8);
-	}
-
-	close(fd);
+	if (memcmp(buf1, buf2, BSZ) != 0)
+		errx(8, "xattr corrupted\n");
 
 	return (0);
 }
diff --git a/tests/zfs-tests/tests/functional/tmpfile/tmpfile_002_pos.c b/tests/zfs-tests/tests/functional/tmpfile/tmpfile_002_pos.c
index 39a72c22a..424231d11 100644
--- a/tests/zfs-tests/tests/functional/tmpfile/tmpfile_002_pos.c
+++ b/tests/zfs-tests/tests/functional/tmpfile/tmpfile_002_pos.c
@@ -6,6 +6,7 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <string.h>
+#include <err.h>
 
 /* backward compat in case it's not defined */
 #ifndef O_TMPFILE
@@ -24,12 +25,27 @@
  *
  */
 
+static void
+run(const char *op)
+{
+	int ret;
+	char buf[50];
+	sprintf(buf, "sudo -E zpool %s $TESTPOOL", op);
+	if ((ret = system(buf)) != 0) {
+		if (ret == -1)
+			err(4, "system \"zpool %s\"", op);
+		else
+			errx(4, "zpool %s exited %d\n",
+			    op, WEXITSTATUS(ret));
+	}
+}
+
 int
 main(void)
 {
-	int i, fd, ret;
+	int i, fd;
 	char spath[1024], dpath[1024];
-	char *penv[] = {"TESTDIR", "TESTFILE0"};
+	const char *penv[] = {"TESTDIR", "TESTFILE0"};
 	struct stat sbuf;
 
 	(void) fprintf(stdout, "Verify O_TMPFILE file can be linked.\n");
@@ -37,55 +53,25 @@ main(void)
 	/*
 	 * Get the environment variable values.
 	 */
-	for (i = 0; i < sizeof (penv) / sizeof (char *); i++) {
-		if ((penv[i] = getenv(penv[i])) == NULL) {
-			(void) fprintf(stderr, "getenv(penv[%d])\n", i);
-			exit(1);
-		}
-	}
+	for (i = 0; i < ARRAY_SIZE(penv); i++)
+		if ((penv[i] = getenv(penv[i])) == NULL)
+			errx(1, "getenv(penv[%d])", i);
 
 	fd = open(penv[0], O_RDWR|O_TMPFILE, 0666);
-	if (fd < 0) {
-		perror("open");
-		exit(2);
-	}
+	if (fd < 0)
+		err(2, "open(%s)", penv[0]);
 
 	snprintf(spath, 1024, "/proc/self/fd/%d", fd);
 	snprintf(dpath, 1024, "%s/%s", penv[0], penv[1]);
-	if (linkat(AT_FDCWD, spath, AT_FDCWD, dpath, AT_SYMLINK_FOLLOW) < 0) {
-		perror("linkat");
-		close(fd);
-		exit(3);
-	}
+	if (linkat(AT_FDCWD, spath, AT_FDCWD, dpath, AT_SYMLINK_FOLLOW) < 0)
+		err(3, "linkat");
 
-	if ((ret = system("sudo -E zpool freeze $TESTPOOL"))) {
-		if (ret == -1)
-			perror("system \"zpool freeze\"");
-		else
-			fprintf(stderr, "zpool freeze exits with %d\n",
-			    WEXITSTATUS(ret));
-		exit(4);
-	}
+	run("freeze");
 
 	close(fd);
 
-	if ((ret = system("sudo -E zpool export $TESTPOOL"))) {
-		if (ret == -1)
-			perror("system \"zpool export\"");
-		else
-			fprintf(stderr, "zpool export exits with %d\n",
-			    WEXITSTATUS(ret));
-		exit(4);
-	}
-
-	if ((ret = system("sudo -E zpool import $TESTPOOL"))) {
-		if (ret == -1)
-			perror("system \"zpool import\"");
-		else
-			fprintf(stderr, "zpool import exits with %d\n",
-			    WEXITSTATUS(ret));
-		exit(4);
-	}
+	run("export");
+	run("import");
 
 	if (stat(dpath, &sbuf) < 0) {
 		perror("stat");
diff --git a/tests/zfs-tests/tests/functional/tmpfile/tmpfile_003_pos.c b/tests/zfs-tests/tests/functional/tmpfile/tmpfile_003_pos.c
index 58aa90512..463b96c99 100644
--- a/tests/zfs-tests/tests/functional/tmpfile/tmpfile_003_pos.c
+++ b/tests/zfs-tests/tests/functional/tmpfile/tmpfile_003_pos.c
@@ -6,6 +6,7 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <string.h>
+#include <err.h>
 
 /* backward compat in case it's not defined */
 #ifndef O_TMPFILE
@@ -28,7 +29,7 @@ main(void)
 {
 	int i, fd;
 	char spath[1024], dpath[1024];
-	char *penv[] = {"TESTDIR", "TESTFILE0"};
+	const char *penv[] = {"TESTDIR", "TESTFILE0"};
 	struct stat sbuf;
 
 	(void) fprintf(stdout, "Verify O_EXCL tmpfile cannot be linked.\n");
@@ -36,33 +37,21 @@ main(void)
 	/*
 	 * Get the environment variable values.
 	 */
-	for (i = 0; i < sizeof (penv) / sizeof (char *); i++) {
-		if ((penv[i] = getenv(penv[i])) == NULL) {
-			(void) fprintf(stderr, "getenv(penv[%d])\n", i);
-			exit(1);
-		}
-	}
+	for (i = 0; i < ARRAY_SIZE(penv); i++)
+		if ((penv[i] = getenv(penv[i])) == NULL)
+			errx(1, "getenv(penv[%d])", i);
 
 	fd = open(penv[0], O_RDWR|O_TMPFILE|O_EXCL, 0666);
-	if (fd < 0) {
-		perror("open");
-		exit(2);
-	}
+	if (fd < 0)
+		err(2, "open(%s)", penv[0]);
 
 	snprintf(spath, 1024, "/proc/self/fd/%d", fd);
 	snprintf(dpath, 1024, "%s/%s", penv[0], penv[1]);
-	if (linkat(AT_FDCWD, spath, AT_FDCWD, dpath, AT_SYMLINK_FOLLOW) == 0) {
-		fprintf(stderr, "linkat returns successfully\n");
-		close(fd);
-		exit(3);
-	}
+	if (linkat(AT_FDCWD, spath, AT_FDCWD, dpath, AT_SYMLINK_FOLLOW) == 0)
+		errx(3, "linkat returned successfully\n");
 
-	if (stat(dpath, &sbuf) == 0) {
-		fprintf(stderr, "stat returns successfully\n");
-		close(fd);
-		exit(4);
-	}
-	close(fd);
+	if (stat(dpath, &sbuf) == 0)
+		errx(4, "stat returned successfully\n");
 
 	return (0);
 }
diff --git a/tests/zfs-tests/tests/functional/tmpfile/tmpfile_stat_mode.c b/tests/zfs-tests/tests/functional/tmpfile/tmpfile_stat_mode.c
index c72ea2bb6..893d2639a 100644
--- a/tests/zfs-tests/tests/functional/tmpfile/tmpfile_stat_mode.c
+++ b/tests/zfs-tests/tests/functional/tmpfile/tmpfile_stat_mode.c
@@ -28,6 +28,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <fcntl.h>
+#include <err.h>
 
 /* backward compat in case it's not defined */
 #ifndef O_TMPFILE
@@ -50,63 +51,46 @@ test_stat_mode(mode_t mask)
 	struct stat st, fst;
 	int i, fd;
 	char spath[1024], dpath[1024];
-	char *penv[] = {"TESTDIR", "TESTFILE0"};
+	const char *penv[] = {"TESTDIR", "TESTFILE0"};
 	mode_t masked = 0777 & ~mask;
 	mode_t mode;
 
 	/*
 	 * Get the environment variable values.
 	 */
-	for (i = 0; i < sizeof (penv) / sizeof (char *); i++) {
-		if ((penv[i] = getenv(penv[i])) == NULL) {
-			fprintf(stderr, "getenv(penv[%d])\n", i);
-			exit(1);
-		}
-	}
+	for (i = 0; i < ARRAY_SIZE(penv); i++)
+		if ((penv[i] = getenv(penv[i])) == NULL)
+			errx(1, "getenv(penv[%d])", i);
 
 	umask(mask);
 	fd = open(penv[0], O_RDWR|O_TMPFILE, 0777);
-	if (fd == -1) {
-		perror("open");
-		exit(2);
-	}
+	if (fd == -1)
+		err(2, "open(%s)", penv[0]);
 
-	if (fstat(fd, &fst) == -1) {
-		perror("fstat");
-		close(fd);
-		exit(3);
-	}
+	if (fstat(fd, &fst) == -1)
+		err(3, "open");
 
 	snprintf(spath, sizeof (spath), "/proc/self/fd/%d", fd);
 	snprintf(dpath, sizeof (dpath), "%s/%s", penv[0], penv[1]);
 
 	unlink(dpath);
-	if (linkat(AT_FDCWD, spath, AT_FDCWD, dpath, AT_SYMLINK_FOLLOW) == -1) {
-		perror("linkat");
-		close(fd);
-		exit(4);
-	}
+	if (linkat(AT_FDCWD, spath, AT_FDCWD, dpath, AT_SYMLINK_FOLLOW) == -1)
+		err(4, "linkat");
 	close(fd);
 
-	if (stat(dpath, &st) == -1) {
-		perror("stat");
-		exit(5);
-	}
+	if (stat(dpath, &st) == -1)
+		err(5, "stat");
 	unlink(dpath);
 
 	/* Verify fstat(2) result */
 	mode = fst.st_mode & 0777;
-	if (mode != masked) {
-		fprintf(stderr, "fstat(2) %o != %o\n", mode, masked);
-		exit(6);
-	}
+	if (mode != masked)
+		errx(6, "fstat(2) %o != %o\n", mode, masked);
 
 	/* Verify stat(2) result */
 	mode = st.st_mode & 0777;
-	if (mode != masked) {
-		fprintf(stderr, "stat(2) %o != %o\n", mode, masked);
-		exit(7);
-	}
+	if (mode != masked)
+		errx(7, "stat(2) %o != %o\n", mode, masked);
 }
 
 int