nvpair: Constify string functions

After addressing coverity complaints involving `nvpair_name()`, the
compiler started complaining about dropping const. This lead to a rabbit
hole where not only `nvpair_name()` needed to be constified, but also
`nvpair_value_string()`, `fnvpair_value_string()` and a few other static
functions, plus variable pointers throughout the code. The result became
a fairly big change, so it has been split out into its own patch.

Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #14612

lib/libzfs/libzfs.abi

@@ -2399,6 +2399,9 @@
     <array-type-def dimensions='1' type-id='a84c031d' size-in-bits='65536' id='163f6aa5'>
       <subrange length='8192' type-id='7359adad' id='c88f397d'/>
     </array-type-def>
+    <array-type-def dimensions='1' type-id='a84c031d' size-in-bits='infinite' id='e84913bd'>
+      <subrange length='infinite' type-id='7359adad' id='031f2035'/>
+    </array-type-def>
     <array-type-def dimensions='1' type-id='9c313c2d' size-in-bits='128' id='c1c22e6c'>
       <subrange length='2' type-id='7359adad' id='52efc4ef'/>
     </array-type-def>
@@ -2456,6 +2459,9 @@
       <data-member access='public' layout-offset-in-bits='96'>
         <var-decl name='nvp_type' type-id='8d0687d2' visibility='default'/>
       </data-member>
+      <data-member access='public' layout-offset-in-bits='128'>
+        <var-decl name='nvp_name' type-id='e84913bd' visibility='default'/>
+      </data-member>
     </class-decl>
     <typedef-decl name='nvpair_t' type-id='1c34e459' id='57928edf'/>
     <class-decl name='drr_begin' size-in-bits='2432' is-struct='yes' visibility='default' id='09fcdc01'>
@@ -2745,7 +2751,7 @@
     </function-decl>
     <function-decl name='nvpair_name' visibility='default' binding='global' size-in-bits='64'>
       <parameter type-id='dace003f'/>
-      <return type-id='26a90f95'/>
+      <return type-id='80f4b756'/>
     </function-decl>
     <function-decl name='fnvpair_value_nvlist' visibility='default' binding='global' size-in-bits='64'>
       <parameter type-id='3fa542f0'/>
@@ -3239,6 +3245,7 @@
     <pointer-type-def type-id='79bd3751' size-in-bits='64' id='c65a1f29'/>
     <qualified-type-def type-id='9b23c9ad' restrict='yes' id='8c85230f'/>
     <qualified-type-def type-id='80f4b756' restrict='yes' id='9d26089a'/>
+    <pointer-type-def type-id='80f4b756' size-in-bits='64' id='7d3cd834'/>
     <qualified-type-def type-id='aca3bac8' const='yes' id='2498fd78'/>
     <pointer-type-def type-id='2498fd78' size-in-bits='64' id='eed6c816'/>
     <qualified-type-def type-id='eed6c816' restrict='yes' id='a431a9da'/>
@@ -3351,9 +3358,9 @@
       <return type-id='95e97e5e'/>
     </function-decl>
     <function-decl name='nvlist_lookup_string' visibility='default' binding='global' size-in-bits='64'>
-      <parameter type-id='5ce45b60'/>
+      <parameter type-id='22cce67b'/>
       <parameter type-id='80f4b756'/>
-      <parameter type-id='9b23c9ad'/>
+      <parameter type-id='7d3cd834'/>
       <return type-id='95e97e5e'/>
     </function-decl>
     <function-decl name='fnvlist_alloc' visibility='default' binding='global' size-in-bits='64'>
@@ -3803,7 +3810,6 @@
     <pointer-type-def type-id='fba6cb51' size-in-bits='64' id='32adbf30'/>
     <pointer-type-def type-id='f20fbd51' size-in-bits='64' id='a3681dea'/>
     <qualified-type-def type-id='26a90f95' restrict='yes' id='266fe297'/>
-    <pointer-type-def type-id='80f4b756' size-in-bits='64' id='7d3cd834'/>
     <qualified-type-def type-id='56fe4a37' const='yes' id='a75125ce'/>
     <pointer-type-def type-id='a75125ce' size-in-bits='64' id='48bea5ec'/>
     <qualified-type-def type-id='8afd6070' const='yes' id='1d853360'/>
@@ -4166,8 +4172,8 @@
       <return type-id='95e97e5e'/>
     </function-decl>
     <function-decl name='nvpair_value_string' visibility='default' binding='global' size-in-bits='64'>
-      <parameter type-id='3fa542f0'/>
-      <parameter type-id='9b23c9ad'/>
+      <parameter type-id='dace003f'/>
+      <parameter type-id='7d3cd834'/>
       <return type-id='95e97e5e'/>
     </function-decl>
     <function-decl name='fnvlist_free' visibility='default' binding='global' size-in-bits='64'>
@@ -4203,9 +4209,9 @@
       <return type-id='9c313c2d'/>
     </function-decl>
     <function-decl name='fnvlist_lookup_string' visibility='default' binding='global' size-in-bits='64'>
-      <parameter type-id='5ce45b60'/>
+      <parameter type-id='22cce67b'/>
       <parameter type-id='80f4b756'/>
-      <return type-id='26a90f95'/>
+      <return type-id='80f4b756'/>
     </function-decl>
     <function-decl name='fnvlist_lookup_nvlist' visibility='default' binding='global' size-in-bits='64'>
       <parameter type-id='5ce45b60'/>
@@ -4418,7 +4424,7 @@
     <function-decl name='getprop_uint64' mangled-name='getprop_uint64' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='getprop_uint64'>
       <parameter type-id='9200a744' name='zhp'/>
       <parameter type-id='58603c44' name='prop'/>
-      <parameter type-id='9b23c9ad' name='source'/>
+      <parameter type-id='7d3cd834' name='source'/>
       <return type-id='9c313c2d'/>
     </function-decl>
     <function-decl name='zfs_prop_get_recvd' mangled-name='zfs_prop_get_recvd' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='zfs_prop_get_recvd'>
@@ -4688,7 +4694,7 @@
       <parameter type-id='95e97e5e'/>
       <parameter type-id='2e45de5d'/>
       <parameter type-id='5ce45b60'/>
-      <parameter type-id='9b23c9ad'/>
+      <parameter type-id='7d3cd834'/>
       <parameter type-id='5d6479ae'/>
       <parameter type-id='80f4b756'/>
       <return type-id='95e97e5e'/>
@@ -5993,8 +5999,8 @@
       <return type-id='9da381c4'/>
     </function-decl>
     <function-decl name='fnvpair_value_string' visibility='default' binding='global' size-in-bits='64'>
-      <parameter type-id='3fa542f0'/>
-      <return type-id='26a90f95'/>
+      <parameter type-id='dace003f'/>
+      <return type-id='80f4b756'/>
     </function-decl>
     <function-decl name='zfeature_is_supported' mangled-name='zfeature_is_supported' visibility='default' binding='global' size-in-bits='64' elf-symbol-id='zfeature_is_supported'>
       <parameter type-id='80f4b756'/>
@@ -8140,8 +8146,8 @@
     <function-decl name='label_paths' visibility='default' binding='global' size-in-bits='64'>
       <parameter type-id='5507783b'/>
       <parameter type-id='5ce45b60'/>
-      <parameter type-id='9b23c9ad'/>
-      <parameter type-id='9b23c9ad'/>
+      <parameter type-id='7d3cd834'/>
+      <parameter type-id='7d3cd834'/>
       <return type-id='95e97e5e'/>
     </function-decl>
     <function-decl name='zutil_alloc' visibility='default' binding='global' size-in-bits='64'>

lib/libzfs/libzfs_crypto.c

@@ -942,7 +942,7 @@ proplist_has_encryption_props(nvlist_t *props)
 {
 	int ret;
 	uint64_t intval;
-	char *strval;
+	const char *strval;
 
 	ret = nvlist_lookup_uint64(props,
 	    zfs_prop_to_name(ZFS_PROP_ENCRYPTION), &intval);
@@ -1007,7 +1007,7 @@ zfs_crypto_create(libzfs_handle_t *hdl, char *parent_name, nvlist_t *props,
 	char errbuf[ERRBUFLEN];
 	uint64_t crypt = ZIO_CRYPT_INHERIT, pcrypt = ZIO_CRYPT_INHERIT;
 	uint64_t keyformat = ZFS_KEYFORMAT_NONE;
-	char *keylocation = NULL;
+	const char *keylocation = NULL;
 	zfs_handle_t *pzhp = NULL;
 	uint8_t *wkeydata = NULL;
 	uint_t wkeylen = 0;
@@ -1595,7 +1595,7 @@ zfs_crypto_rewrap(zfs_handle_t *zhp, nvlist_t *raw_props, boolean_t inheritkey)
 	uint64_t crypt, pcrypt, keystatus, pkeystatus;
 	uint64_t keyformat = ZFS_KEYFORMAT_NONE;
 	zfs_handle_t *pzhp = NULL;
-	char *keylocation = NULL;
+	const char *keylocation = NULL;
 	char origin_name[MAXNAMELEN];
 	char prop_keylocation[MAXNAMELEN];
 	char parent_name[ZFS_MAX_DATASET_NAME_LEN];
@@ -1705,7 +1705,7 @@ 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 = (char *)"prompt";
+				keylocation = "prompt";
 				ret = nvlist_add_string(props,
 				    zfs_prop_to_name(ZFS_PROP_KEYLOCATION),
 				    keylocation);

lib/libzfs/libzfs_dataset.c

@@ -1029,7 +1029,7 @@ zfs_valid_proplist(libzfs_handle_t *hdl, zfs_type_t type, nvlist_t *nvl,
 {
 	nvpair_t *elem;
 	uint64_t intval;
-	char *strval;
+	const char *strval;
 	zfs_prop_t prop;
 	nvlist_t *ret;
 	int chosen_normal = -1;
@@ -2065,7 +2065,7 @@ error:
  * extract them appropriately.
  */
 uint64_t
-getprop_uint64(zfs_handle_t *zhp, zfs_prop_t prop, char **source)
+getprop_uint64(zfs_handle_t *zhp, zfs_prop_t prop, const char **source)
 {
 	nvlist_t *nv;
 	uint64_t value;
@@ -2079,14 +2079,14 @@ 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 = (char *)"";
+		*source = "";
 	}
 
 	return (value);
 }
 
 static const char *
-getprop_string(zfs_handle_t *zhp, zfs_prop_t prop, char **source)
+getprop_string(zfs_handle_t *zhp, zfs_prop_t prop, const char **source)
 {
 	nvlist_t *nv;
 	const char *value;
@@ -2100,7 +2100,7 @@ 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 = (char *)"";
+		*source = "";
 	}
 
 	return (value);
@@ -2138,7 +2138,7 @@ zfs_unset_recvd_props_mode(zfs_handle_t *zhp, uintptr_t *cookie)
  */
 static int
 get_numeric_property(zfs_handle_t *zhp, zfs_prop_t prop, zprop_source_t *src,
-    char **source, uint64_t *val)
+    const char **source, uint64_t *val)
 {
 	zfs_cmd_t zc = {"\0"};
 	nvlist_t *zplprops = NULL;
@@ -2370,7 +2370,7 @@ get_numeric_property(zfs_handle_t *zhp, zfs_prop_t prop, zprop_source_t *src,
  * Calculate the source type, given the raw source string.
  */
 static void
-get_source(zfs_handle_t *zhp, zprop_source_t *srctype, char *source,
+get_source(zfs_handle_t *zhp, zprop_source_t *srctype, const char *source,
     char *statbuf, size_t statlen)
 {
 	if (statbuf == NULL ||
@@ -2418,7 +2418,7 @@ zfs_prop_get_recvd(zfs_handle_t *zhp, const char *propname, char *propbuf,
 		zfs_unset_recvd_props_mode(zhp, &cookie);
 	} else {
 		nvlist_t *propval;
-		char *recvdval;
+		const char *recvdval;
 		if (nvlist_lookup_nvlist(zhp->zfs_recvd_props,
 		    propname, &propval) != 0)
 			return (-1);
@@ -2620,7 +2620,7 @@ zcp_check(zfs_handle_t *zhp, zfs_prop_t prop, uint64_t intval,
 				    (u_longlong_t)intval, (u_longlong_t)ans);
 			}
 		} else {
-			char *str_ans;
+			const char *str_ans;
 			error = nvlist_lookup_string(retnvl, "value", &str_ans);
 			if (error != 0) {
 				(void) fprintf(stderr, "%s: zcp check error: "
@@ -2652,7 +2652,7 @@ int
 zfs_prop_get(zfs_handle_t *zhp, zfs_prop_t prop, char *propbuf, size_t proplen,
     zprop_source_t *src, char *statbuf, size_t statlen, boolean_t literal)
 {
-	char *source = NULL;
+	const char *source = NULL;
 	uint64_t val;
 	const char *str;
 	const char *strval;
@@ -3053,7 +3053,7 @@ zfs_prop_get(zfs_handle_t *zhp, zfs_prop_t prop, char *propbuf, size_t proplen,
 uint64_t
 zfs_prop_get_int(zfs_handle_t *zhp, zfs_prop_t prop)
 {
-	char *source;
+	const char *source;
 	uint64_t val = 0;
 
 	(void) get_numeric_property(zhp, prop, NULL, &source, &val);
@@ -3077,7 +3077,7 @@ int
 zfs_prop_get_numeric(zfs_handle_t *zhp, zfs_prop_t prop, uint64_t *value,
     zprop_source_t *src, char *statbuf, size_t statlen)
 {
-	char *source;
+	const char *source;
 
 	/*
 	 * Check to see if this property applies to our object
@@ -4698,7 +4698,7 @@ zfs_expand_proplist(zfs_handle_t *zhp, zprop_list_t **plp, boolean_t received,
 	zprop_list_t **last, **start;
 	nvlist_t *userprops, *propval;
 	nvpair_t *elem;
-	char *strval;
+	const char *strval;
 	char buf[ZFS_MAXPROPLEN];
 
 	if (zprop_expand_list(hdl, plp, ZFS_TYPE_DATASET) != 0)
@@ -5484,7 +5484,7 @@ volsize_from_vdevs(zpool_handle_t *zhp, uint64_t nblocks, uint64_t blksize)
 	}
 
 	for (int v = 0; v < nvdevs; v++) {
-		char *type;
+		const char *type;
 		uint64_t nparity, ashift, asize, tsize;
 		uint64_t volsize;
 
@@ -5566,7 +5566,7 @@ zvol_volsize_to_reservation(zpool_handle_t *zph, uint64_t volsize,
 	uint64_t numdb;
 	uint64_t nblocks, volblocksize;
 	int ncopies;
-	char *strval;
+	const char *strval;
 
 	if (nvlist_lookup_string(props,
 	    zfs_prop_to_name(ZFS_PROP_COPIES), &strval) == 0)

lib/libzfs/libzfs_impl.h

@@ -140,7 +140,7 @@ extern zfs_handle_t *make_dataset_handle_zc(libzfs_handle_t *, zfs_cmd_t *);
 extern zfs_handle_t *make_dataset_simple_handle_zc(zfs_handle_t *, zfs_cmd_t *);
 
 extern int zprop_parse_value(libzfs_handle_t *, nvpair_t *, int, zfs_type_t,
-    nvlist_t *, char **, uint64_t *, const char *);
+    nvlist_t *, const char **, uint64_t *, const char *);
 extern int zprop_expand_list(libzfs_handle_t *hdl, zprop_list_t **plp,
     zfs_type_t type);
 

lib/libzfs/libzfs_import.c

@@ -280,7 +280,7 @@ zpool_in_use(libzfs_handle_t *hdl, int fd, pool_state_t *state, char **namestr,
     boolean_t *inuse)
 {
 	nvlist_t *config;
-	char *name = NULL;
+	const char *name = NULL;
 	boolean_t ret;
 	uint64_t guid = 0, vdev_guid;
 	zpool_handle_t *zhp;

lib/libzfs/libzfs_iter.c

@@ -224,7 +224,7 @@ zfs_iter_bookmarks(zfs_handle_t *zhp, int flags __maybe_unused,
 	for (pair = nvlist_next_nvpair(bmarks, NULL);
 	    pair != NULL; pair = nvlist_next_nvpair(bmarks, pair)) {
 		char name[ZFS_MAX_DATASET_NAME_LEN];
-		char *bmark_name;
+		const char *bmark_name;
 		nvlist_t *bmark_props;
 
 		bmark_name = nvpair_name(pair);

lib/libzfs/libzfs_mount.c

@@ -291,7 +291,7 @@ static int
 zfs_add_option(zfs_handle_t *zhp, char *options, int len,
     zfs_prop_t prop, const char *on, const char *off)
 {
-	char *source;
+	const char *source;
 	uint64_t value;
 
 	/* Skip adding duplicate default options */

lib/libzfs/libzfs_pool.c

@@ -459,9 +459,9 @@ zpool_valid_proplist(libzfs_handle_t *hdl, const char *poolname,
 	nvpair_t *elem;
 	nvlist_t *retprops;
 	zpool_prop_t prop;
-	char *strval;
+	const char *strval;
 	uint64_t intval;
-	char *slash, *check;
+	const char *slash, *check;
 	struct stat64 statbuf;
 	zpool_handle_t *zhp;
 	char report[1024];
@@ -689,12 +689,12 @@ zpool_valid_proplist(libzfs_handle_t *hdl, const char *poolname,
 				goto error;
 			}
 
-			*slash = '\0';
+			*(char *)slash = '\0';
 
 			if (strval[0] != '\0' &&
 			    (stat64(strval, &statbuf) != 0 ||
 			    !S_ISDIR(statbuf.st_mode))) {
-				*slash = '/';
+				*(char *)slash = '/';
 				zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
 				    "'%s' is not a valid directory"),
 				    strval);
@@ -702,7 +702,7 @@ zpool_valid_proplist(libzfs_handle_t *hdl, const char *poolname,
 				goto error;
 			}
 
-			*slash = '/';
+			*(char *)slash = '/';
 			break;
 
 		case ZPOOL_PROP_COMPATIBILITY:
@@ -932,7 +932,7 @@ vdev_expand_proplist(zpool_handle_t *zhp, const char *vdevname,
 {
 	zprop_list_t *entry;
 	char buf[ZFS_MAXPROPLEN];
-	char *strval = NULL;
+	const char *strval = NULL;
 	int err = 0;
 	nvpair_t *elem = NULL;
 	nvlist_t *vprops = NULL;
@@ -1290,7 +1290,7 @@ zpool_has_special_vdev(nvlist_t *nvroot)
 	if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_CHILDREN, &child,
 	    &children) == 0) {
 		for (uint_t c = 0; c < children; c++) {
-			char *bias;
+			const char *bias;
 
 			if (nvlist_lookup_string(child[c],
 			    ZPOOL_CONFIG_ALLOCATION_BIAS, &bias) == 0 &&
@@ -1314,7 +1314,7 @@ zpool_has_draid_vdev(nvlist_t *nvroot)
 	if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_CHILDREN,
 	    &child, &children) == 0) {
 		for (uint_t c = 0; c < children; c++) {
-			char *type;
+			const char *type;
 
 			if (nvlist_lookup_string(child[c],
 			    ZPOOL_CONFIG_TYPE, &type) == 0 &&
@@ -1394,7 +1394,7 @@ zpool_create(libzfs_handle_t *hdl, const char *pool, nvlist_t *nvroot,
 
 	if (fsprops) {
 		uint64_t zoned;
-		char *zonestr;
+		const char *zonestr;
 
 		zoned = ((nvlist_lookup_string(fsprops,
 		    zfs_prop_to_name(ZFS_PROP_ZONED), &zonestr) == 0) &&
@@ -1987,7 +1987,7 @@ zpool_print_unsup_feat(nvlist_t *config)
 
 	for (nvpair_t *nvp = nvlist_next_nvpair(unsup_feat, NULL);
 	    nvp != NULL; nvp = nvlist_next_nvpair(unsup_feat, nvp)) {
-		char *desc = fnvpair_value_string(nvp);
+		const char *desc = fnvpair_value_string(nvp);
 		if (strlen(desc) > 0)
 			(void) printf("\t%s (%s)\n", nvpair_name(nvp), desc);
 		else
@@ -2011,7 +2011,7 @@ zpool_import_props(libzfs_handle_t *hdl, nvlist_t *config, const char *newname,
 	nvlist_t *nvinfo = NULL;
 	nvlist_t *missing = NULL;
 	const char *thename;
-	char *origname;
+	const char *origname;
 	int ret;
 	int error = 0;
 	char errbuf[ERRBUFLEN];
@@ -2239,7 +2239,7 @@ zpool_translate_vdev_guids(zpool_handle_t *zhp, nvlist_t *vds,
 	    elem = nvlist_next_nvpair(vds, elem)) {
 		boolean_t spare, cache;
 
-		char *vd_path = nvpair_name(elem);
+		const char *vd_path = nvpair_name(elem);
 		nvlist_t *tgt = zpool_find_vdev(zhp, vd_path, &spare, &cache,
 		    NULL);
 
@@ -2353,7 +2353,7 @@ list_errors:
 	for (elem = nvlist_next_nvpair(vd_errlist, NULL); elem != NULL;
 	    elem = nvlist_next_nvpair(vd_errlist, elem)) {
 		int64_t vd_error = xlate_init_err(fnvpair_value_int64(elem));
-		char *path;
+		const char *path;
 
 		if (nvlist_lookup_string(guids_to_paths, nvpair_name(elem),
 		    &path) != 0)
@@ -2451,7 +2451,7 @@ check_trim_errs(zpool_handle_t *zhp, trimflags_t *trim_flags,
 	for (elem = nvlist_next_nvpair(errlist, NULL);
 	    elem != NULL; elem = nvlist_next_nvpair(errlist, elem)) {
 		int64_t vd_error = xlate_trim_err(fnvpair_value_int64(elem));
-		char *path;
+		const char *path;
 
 		/*
 		 * If only the pool was specified, and it was not a secure
@@ -2634,7 +2634,7 @@ vdev_to_nvlist_iter(nvlist_t *nv, nvlist_t *search, boolean_t *avail_spare,
 	nvlist_t **child;
 	nvlist_t *ret;
 	uint64_t is_log;
-	char *srchkey;
+	const char *srchkey;
 	nvpair_t *pair = nvlist_next_nvpair(search, NULL);
 
 	/* Nothing to look for */
@@ -2656,7 +2656,7 @@ vdev_to_nvlist_iter(nvlist_t *nv, nvlist_t *search, boolean_t *avail_spare,
 		break;
 
 	case DATA_TYPE_STRING: {
-		char *srchval, *val;
+		const char *srchval, *val;
 
 		srchval = fnvpair_value_string(pair);
 		if (nvlist_lookup_string(nv, srchkey, &val) != 0)
@@ -2969,7 +2969,7 @@ zpool_vdev_online(zpool_handle_t *zhp, const char *path, int flags,
 		return (zfs_error(hdl, EZFS_ISSPARE, errbuf));
 
 #ifndef __FreeBSD__
-	char *pathname;
+	const char *pathname;
 	if ((flags & ZFS_ONLINE_EXPAND ||
 	    zpool_get_prop_int(zhp, ZPOOL_PROP_AUTOEXPAND, NULL)) &&
 	    nvlist_lookup_string(tgt, ZPOOL_CONFIG_PATH, &pathname) == 0) {
@@ -3181,7 +3181,8 @@ is_replacing_spare(nvlist_t *search, nvlist_t *tgt, int which)
 
 	if (nvlist_lookup_nvlist_array(search, ZPOOL_CONFIG_CHILDREN, &child,
 	    &children) == 0) {
-		char *type = fnvlist_lookup_string(search, ZPOOL_CONFIG_TYPE);
+		const char *type = fnvlist_lookup_string(search,
+		    ZPOOL_CONFIG_TYPE);
 		if ((strcmp(type, VDEV_TYPE_SPARE) == 0 ||
 		    strcmp(type, VDEV_TYPE_DRAID_SPARE) == 0) &&
 		    children == 2 && child[which] == tgt)
@@ -3484,7 +3485,8 @@ zpool_vdev_split(zpool_handle_t *zhp, char *newname, nvlist_t **newroot,
     nvlist_t *props, splitflags_t flags)
 {
 	zfs_cmd_t zc = {"\0"};
-	char errbuf[ERRBUFLEN], *bias;
+	char errbuf[ERRBUFLEN];
+	const char *bias;
 	nvlist_t *tree, *config, **child, **newchild, *newconfig = NULL;
 	nvlist_t **varray = NULL, *zc_props = NULL;
 	uint_t c, children, newchildren, lastlog = 0, vcount, found = 0;
@@ -3542,7 +3544,7 @@ zpool_vdev_split(zpool_handle_t *zhp, char *newname, nvlist_t **newroot,
 	for (c = 0; c < children; c++) {
 		uint64_t is_log = B_FALSE, is_hole = B_FALSE;
 		boolean_t is_special = B_FALSE, is_dedup = B_FALSE;
-		char *type;
+		const char *type;
 		nvlist_t **mchild, *vdev;
 		uint_t mchildren;
 		int entry;
@@ -4015,7 +4017,7 @@ char *
 zpool_vdev_name(libzfs_handle_t *hdl, zpool_handle_t *zhp, nvlist_t *nv,
     int name_flags)
 {
-	char *type, *tpath;
+	const char *type, *tpath;
 	const char *path;
 	uint64_t value;
 	char buf[PATH_BUF_LEN];

lib/libzfs/libzfs_sendrecv.c

@@ -119,7 +119,7 @@ dump_record(dmu_replay_record_t *drr, void *payload, size_t payload_len,
 typedef struct fsavl_node {
 	avl_node_t fn_node;
 	nvlist_t *fn_nvfs;
-	char *fn_snapname;
+	const char *fn_snapname;
 	uint64_t fn_guid;
 } fsavl_node_t;
 
@@ -137,7 +137,7 @@ fsavl_compare(const void *arg1, const void *arg2)
  * (optionally) name.
  */
 static nvlist_t *
-fsavl_find(avl_tree_t *avl, uint64_t snapguid, char **snapname)
+fsavl_find(avl_tree_t *avl, uint64_t snapguid, const char **snapname)
 {
 	fsavl_node_t fn_find;
 	fsavl_node_t *fn;
@@ -384,7 +384,7 @@ send_iterate_prop(zfs_handle_t *zhp, boolean_t received_only, nvlist_t *nv)
 
 	nvpair_t *elem = NULL;
 	while ((elem = nvlist_next_nvpair(props, elem)) != NULL) {
-		char *propname = nvpair_name(elem);
+		const char *propname = nvpair_name(elem);
 		zfs_prop_t prop = zfs_name_to_prop(propname);
 
 		if (!zfs_prop_user(propname)) {
@@ -412,7 +412,7 @@ send_iterate_prop(zfs_handle_t *zhp, boolean_t received_only, nvlist_t *nv)
 		if (isspacelimit && zhp->zfs_type == ZFS_TYPE_SNAPSHOT)
 			continue;
 
-		char *source;
+		const char *source;
 		if (nvlist_lookup_string(propnv, ZPROP_SOURCE, &source) == 0) {
 			if (strcmp(source, zhp->zfs_name) != 0 &&
 			    strcmp(source, ZPROP_SOURCE_VAL_RECVD) != 0)
@@ -428,7 +428,7 @@ send_iterate_prop(zfs_handle_t *zhp, boolean_t received_only, nvlist_t *nv)
 
 		if (zfs_prop_user(propname) ||
 		    zfs_prop_get_type(prop) == PROP_TYPE_STRING) {
-			char *value;
+			const char *value;
 			value = fnvlist_lookup_string(propnv, ZPROP_VALUE);
 			fnvlist_add_string(nv, propname, value);
 		} else {
@@ -1132,7 +1132,7 @@ dump_snapshot(zfs_handle_t *zhp, void *arg)
 
 	if (!sdd->doall && !isfromsnap && !istosnap) {
 		if (sdd->replicate) {
-			char *snapname;
+			const char *snapname;
 			nvlist_t *snapprops;
 			/*
 			 * Filter out all intermediate snapshots except origin
@@ -1372,7 +1372,7 @@ dump_filesystems(zfs_handle_t *rzhp, send_dump_data_t *sdd)
 		nvfs = fnvpair_value_nvlist(fspair);
 		(void) nvlist_lookup_uint64(nvfs, "origin", &origin_guid);
 		if (origin_guid != 0) {
-			char *snapname;
+			const char *snapname;
 			nvlist_t *origin_nv = fsavl_find(sdd->fsavl,
 			    origin_guid, &snapname);
 			if (origin_nv != NULL) {
@@ -1391,7 +1391,7 @@ again:
 	for (fspair = nvlist_next_nvpair(sdd->fss, NULL); fspair;
 	    fspair = nvlist_next_nvpair(sdd->fss, fspair)) {
 		nvlist_t *fslist, *parent_nv;
-		char *fsname;
+		const char *fsname;
 		zfs_handle_t *zhp;
 		int err;
 		uint64_t origin_guid = 0;
@@ -1757,8 +1757,8 @@ zfs_send_resume_impl_cb_impl(libzfs_handle_t *hdl, sendflags_t *flags,
     int outfd, nvlist_t *resume_nvl)
 {
 	char errbuf[ERRBUFLEN];
-	char *toname;
-	char *fromname = NULL;
+	const char *toname;
+	const char *fromname = NULL;
 	uint64_t resumeobj, resumeoff, toguid, fromguid, bytes;
 	zfs_handle_t *zhp;
 	int error = 0;
@@ -3254,7 +3254,7 @@ created_before(libzfs_handle_t *hdl, avl_tree_t *avl,
     uint64_t guid1, uint64_t guid2)
 {
 	nvlist_t *nvfs;
-	char *fsname = NULL, *snapname = NULL;
+	const char *fsname = NULL, *snapname = NULL;
 	char buf[ZFS_MAX_DATASET_NAME_LEN];
 	int rv;
 	zfs_handle_t *guid1hdl, *guid2hdl;
@@ -3320,7 +3320,7 @@ recv_fix_encryption_hierarchy(libzfs_handle_t *hdl, const char *top_zfs,
 		nvpair_t *snapel = NULL;
 		boolean_t is_encroot, is_clone, stream_encroot;
 		char *cp;
-		char *stream_keylocation = NULL;
+		const char *stream_keylocation = NULL;
 		char keylocation[MAXNAMELEN];
 		char fsname[ZFS_MAX_DATASET_NAME_LEN];
 
@@ -3440,12 +3440,12 @@ recv_incremental_replication(libzfs_handle_t *hdl, const char *tofs,
 	nvlist_t *local_nv, *deleted = NULL;
 	avl_tree_t *local_avl;
 	nvpair_t *fselem, *nextfselem;
-	char *fromsnap;
+	const char *fromsnap;
 	char newname[ZFS_MAX_DATASET_NAME_LEN];
 	char guidname[32];
 	int error;
 	boolean_t needagain, progress, recursive;
-	char *s1, *s2;
+	const char *s1, *s2;
 
 	fromsnap = fnvlist_lookup_string(stream_nv, "fromsnap");
 
@@ -3477,7 +3477,7 @@ again:
 		uint64_t originguid = 0;
 		uint64_t stream_originguid = 0;
 		uint64_t parent_fromsnap_guid, stream_parent_fromsnap_guid;
-		char *fsname, *stream_fsname;
+		const char *fsname, *stream_fsname;
 
 		nextfselem = nvlist_next_nvpair(local_nv, fselem);
 
@@ -3512,7 +3512,7 @@ again:
 			case 1: {
 				/* promote it! */
 				nvlist_t *origin_nvfs;
-				char *origin_fsname;
+				const char *origin_fsname;
 
 				origin_nvfs = fsavl_find(local_avl, originguid,
 				    NULL);
@@ -3543,7 +3543,7 @@ again:
 		for (snapelem = nvlist_next_nvpair(snaps, NULL);
 		    snapelem; snapelem = nextsnapelem) {
 			uint64_t thisguid;
-			char *stream_snapname;
+			const char *stream_snapname;
 			nvlist_t *found, *props;
 
 			nextsnapelem = nvlist_next_nvpair(snaps, snapelem);
@@ -3689,7 +3689,7 @@ again:
 			 * new fs.
 			 */
 			if (parent != NULL) {
-				char *pname;
+				const char *pname;
 
 				pname = fnvlist_lookup_string(parent, "name");
 				(void) snprintf(tryname, sizeof (tryname),
@@ -3740,8 +3740,8 @@ zfs_receive_package(libzfs_handle_t *hdl, int fd, const char *destname,
 {
 	nvlist_t *stream_nv = NULL;
 	avl_tree_t *stream_avl = NULL;
-	char *fromsnap = NULL;
-	char *sendsnap = NULL;
+	const char *fromsnap = NULL;
+	const char *sendsnap = NULL;
 	char *cp;
 	char tofs[ZFS_MAX_DATASET_NAME_LEN];
 	char sendfs[ZFS_MAX_DATASET_NAME_LEN];
@@ -4230,7 +4230,7 @@ zfs_setup_cmdline_props(libzfs_handle_t *hdl, zfs_type_t type,
 			 */
 			if (nvlist_exists(origprops, newname)) {
 				nvlist_t *attrs;
-				char *source = NULL;
+				const char *source = NULL;
 
 				attrs = fnvlist_lookup_nvlist(origprops,
 				    newname);
@@ -4354,7 +4354,7 @@ zfs_receive_one(libzfs_handle_t *hdl, int infd, const char *tosnap,
 	zprop_errflags_t prop_errflags;
 	nvlist_t *prop_errors = NULL;
 	boolean_t recursive;
-	char *snapname = NULL;
+	const char *snapname = NULL;
 	char destsnap[MAXPATHLEN * 2];
 	char origin[MAXNAMELEN] = {0};
 	char name[MAXPATHLEN];
@@ -4385,7 +4385,7 @@ zfs_receive_one(libzfs_handle_t *hdl, int infd, const char *tosnap,
 	boolean_t holds = flags->holds && !flags->skipholds;
 
 	if (stream_avl != NULL) {
-		char *keylocation = NULL;
+		const char *keylocation = NULL;
 		nvlist_t *lookup = NULL;
 		nvlist_t *fs = fsavl_find(stream_avl, drrb->drr_toguid,
 		    &snapname);
@@ -5503,7 +5503,7 @@ zfs_receive(libzfs_handle_t *hdl, const char *tosnap, nvlist_t *props,
 	char *top_zfs = NULL;
 	int err;
 	struct stat sb;
-	char *originsnap = NULL;
+	const char *originsnap = NULL;
 
 	/*
 	 * The only way fstat can fail is if we do not have a valid file

lib/libzfs/libzfs_status.c

@@ -168,7 +168,8 @@ find_vdev_problem(nvlist_t *vdev, int (*func)(vdev_stat_t *, uint_t),
 	 * later.
 	 */
 	if (ignore_replacing == B_TRUE) {
-		char *type = fnvlist_lookup_string(vdev, ZPOOL_CONFIG_TYPE);
+		const char *type = fnvlist_lookup_string(vdev,
+		    ZPOOL_CONFIG_TYPE);
 		if (strcmp(type, VDEV_TYPE_REPLACING) == 0)
 			return (B_FALSE);
 	}

lib/libzfs/libzfs_util.c

@@ -1595,13 +1595,13 @@ zfs_nicestrtonum(libzfs_handle_t *hdl, const char *value, uint64_t *num)
  */
 int
 zprop_parse_value(libzfs_handle_t *hdl, nvpair_t *elem, int prop,
-    zfs_type_t type, nvlist_t *ret, char **svalp, uint64_t *ivalp,
+    zfs_type_t type, nvlist_t *ret, const char **svalp, uint64_t *ivalp,
     const char *errbuf)
 {
 	data_type_t datatype = nvpair_type(elem);
 	zprop_type_t proptype;
 	const char *propname;
-	char *value;
+	const char *value;
 	boolean_t isnone = B_FALSE;
 	boolean_t isauto = B_FALSE;
 	int err = 0;

lib/libzfs/os/linux/libzfs_pool_os.c

@@ -96,7 +96,7 @@ zpool_relabel_disk(libzfs_handle_t *hdl, const char *path, const char *msg)
 static int
 read_efi_label(nvlist_t *config, diskaddr_t *sb)
 {
-	char *path;
+	const char *path;
 	int fd;
 	char diskname[MAXPATHLEN];
 	int err = -1;