libzpool: tunable-based option interface for zdb/ztest

Removes the old dlsym() based option setter and adds a new
function handle_tunable_option() that can set, get and list all the
tunables in the system. And then wire it up to zdb and ztest.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #17537

cmd/zdb/zdb.c

@@ -797,8 +797,8 @@ usage(void)
 	    "[default is 200]\n");
 	(void) fprintf(stderr, "        -K --key=KEY                 "
 	    "decryption key for encrypted dataset\n");
-	(void) fprintf(stderr, "        -o --option=\"OPTION=INTEGER\" "
-	    "set global variable to an unsigned 32-bit integer\n");
+	(void) fprintf(stderr, "        -o --option=\"NAME=VALUE\" "
+	    "set the named tunable to the given value\n");
 	(void) fprintf(stderr, "        -p --path==PATH              "
 	    "use one or more with -e to specify path to vdev dir\n");
 	(void) fprintf(stderr, "        -P --parseable               "
@@ -9377,9 +9377,11 @@ main(int argc, char **argv)
 			while (*optarg != '\0') { *optarg++ = '*'; }
 			break;
 		case 'o':
-			error = set_global_var(optarg);
+			dump_opt[c]++;
+			dump_all = 0;
+			error = handle_tunable_option(optarg, B_FALSE);
 			if (error != 0)
-				usage();
+				zdb_exit(1);
 			break;
 		case 'p':
 			if (searchdirs == NULL) {
@@ -9545,6 +9547,12 @@ main(int argc, char **argv)
 			error = 0;
 			goto fini;
 		}
+		if (dump_opt['o'])
+			/*
+			 * Avoid blasting tunable options off the top of the
+			 * screen.
+			 */
+			zdb_exit(1);
 		usage();
 	}
 

cmd/ztest.c

@@ -809,8 +809,8 @@ static ztest_option_t option_table[] = {
 	{ 'X', "raidz-expansion", NULL,
 	    "Perform a dedicated raidz expansion test",
 	    NO_DEFAULT, NULL},
-	{ 'o',	"option", "\"OPTION=INTEGER\"",
-	    "Set global variable to an unsigned 32-bit integer value",
+	{ 'o',	"option", "\"NAME=VALUE\"",
+	    "Set the named tunable to the given value",
 	    NO_DEFAULT, NULL},
 	{ 'G',	"dump-debug-msg", NULL,
 	    "Dump zfs_dbgmsg buffer before exiting due to an error",
@@ -7069,7 +7069,7 @@ ztest_set_global_vars(void)
 		char *kv = ztest_opts.zo_gvars[i];
 		VERIFY3U(strlen(kv), <=, ZO_GVARS_MAX_ARGLEN);
 		VERIFY3U(strlen(kv), >, 0);
-		int err = set_global_var(kv);
+		int err = handle_tunable_option(kv, B_TRUE);
 		if (ztest_opts.zo_verbose > 0) {
 			(void) printf("setting global var %s ... %s\n", kv,
 			    err ? "failed" : "ok");

include/sys/zfs_context.h

@@ -661,7 +661,7 @@ extern void random_fini(void);
 
 struct spa;
 extern void show_pool_stats(struct spa *);
-extern int set_global_var(char const *arg);
+extern int handle_tunable_option(const char *, boolean_t);
 
 typedef struct callb_cpr {
 	kmutex_t	*cc_lockp;

lib/libzpool/Makefile.am

@@ -199,7 +199,7 @@ libzpool_la_LIBADD = \
 	libzstd.la \
 	libzutil.la
 
-libzpool_la_LIBADD += $(LIBCLOCK_GETTIME) $(ZLIB_LIBS) -ldl -lm
+libzpool_la_LIBADD += $(LIBCLOCK_GETTIME) $(ZLIB_LIBS) -lm
 
 libzpool_la_LDFLAGS = -pthread
 

lib/libzpool/util.c

@@ -36,7 +36,7 @@
 #include <sys/fs/zfs.h>
 #include <sys/zfs_refcount.h>
 #include <sys/zfs_ioctl.h>
-#include <dlfcn.h>
+#include <sys/tunables.h>
 #include <libzutil.h>
 
 /*
@@ -151,97 +151,119 @@ show_pool_stats(spa_t *spa)
 	nvlist_free(config);
 }
 
-/* *k_out must be freed by the caller */
-static int
-set_global_var_parse_kv(const char *arg, char **k_out, u_longlong_t *v_out)
-{
-	int err;
-	VERIFY(arg);
-	char *d = strdup(arg);
-
-	char *save = NULL;
-	char *k = strtok_r(d, "=", &save);
-	char *v_str = strtok_r(NULL, "=", &save);
-	char *follow = strtok_r(NULL, "=", &save);
-	if (k == NULL || v_str == NULL || follow != NULL) {
-		err = EINVAL;
-		goto err_free;
-	}
-
-	u_longlong_t val = strtoull(v_str, NULL, 0);
-	if (val > UINT32_MAX) {
-		fprintf(stderr, "Value for global variable '%s' must "
-		    "be a 32-bit unsigned integer, got '%s'\n", k, v_str);
-		err = EOVERFLOW;
-		goto err_free;
-	}
-
-	*k_out = strdup(k);
-	*v_out = val;
-	free(d);
-	return (0);
-
-err_free:
-	free(d);
-
-	return (err);
-}
-
 /*
- * Sets given global variable in libzpool to given unsigned 32-bit value.
- * arg: "<variable>=<value>"
+ * Common helper for working with libzpool tunables from the command line.
+ *
+ * Valid inputs:
+ *
+ *   <name>		show named tunable and value
+ *   <name>=<value>	set tunable value
+ *
+ *   show		show all tunables and values
+ *   show=<name>	show named tunable and value
+ *   info		show info about all tunables
+ *   info=<name>	show info about named tunable
  */
-int
-set_global_var(char const *arg)
+
+typedef enum { SHOW, INFO, SET } tunable_mode_t;
+
+static int
+list_tunables_cb(const zfs_tunable_t *tunable, void *arg)
 {
-	void *zpoolhdl;
-	char *varname;
-	u_longlong_t val;
-	int ret;
+	const tunable_mode_t *mode = arg;
 
-#ifndef _ZFS_LITTLE_ENDIAN
-	/*
-	 * On big endian systems changing a 64-bit variable would set the high
-	 * 32 bits instead of the low 32 bits, which could cause unexpected
-	 * results.
-	 */
-	fprintf(stderr, "Setting global variables is only supported on "
-	    "little-endian systems\n");
-	ret = ENOTSUP;
-	goto out_ret;
-#endif
-
-	if ((ret = set_global_var_parse_kv(arg, &varname, &val)) != 0) {
-		goto out_ret;
-	}
-
-	zpoolhdl = dlopen("libzpool.so", RTLD_LAZY);
-	if (zpoolhdl != NULL) {
-		uint32_t *var;
-		var = dlsym(zpoolhdl, varname);
-		if (var == NULL) {
-			fprintf(stderr, "Global variable '%s' does not exist "
-			    "in libzpool.so\n", varname);
-			ret = EINVAL;
-			goto out_dlclose;
-		}
-		*var = (uint32_t)val;
+	static const char *type[] = {
+		"int", "uint", "ulong", "u64", "str",
+	};
+	static const char *perm[] = {
+		"rw", "rd",
+	};
 
+	if (*mode == SHOW) {
+		char val[64];
+		int err = zfs_tunable_get(tunable, val, sizeof (val));
+		if (err == 0)
+			printf("%s: %s\n", tunable->zt_name, val);
+		else
+			printf("%s: [error getting tunable value: %s]\n",
+			    tunable->zt_name, strerror(err));
 	} else {
-		fprintf(stderr, "Failed to open libzpool.so to set global "
-		    "variable\n");
-		ret = EIO;
-		goto out_free;
+		printf("%s [%s %s]: %s\n", tunable->zt_name,
+		    type[tunable->zt_type], perm[tunable->zt_perm],
+		    tunable->zt_desc);
 	}
 
-	ret = 0;
+	return (0);
+}
+int
+handle_tunable_option(const char *_arg, boolean_t quiet)
+{
+	int err = 0;
+	char *arg = strdup(_arg);
+	char *k, *v;
 
-out_dlclose:
-	dlclose(zpoolhdl);
-out_free:
-	free(varname);
-out_ret:
-	return (ret);
+	v = arg;
+	k = strsep(&v, "=");
+
+	tunable_mode_t mode;
+
+	if (strcmp(k, "show") == 0) {
+		mode = SHOW;
+		k = v;
+	} else if (strcmp(k, "info") == 0) {
+		mode = INFO;
+		k = v;
+	} else if (v == NULL) {
+		mode = SHOW;
+	} else {
+		mode = SET;
+	}
+
+	if (quiet && mode != SET) {
+		err = EINVAL;
+		goto out;
+	}
+
+	if (mode == SET) {
+		const zfs_tunable_t *tunable = zfs_tunable_lookup(k);
+		if (tunable == NULL) {
+			err = ENOENT;
+			goto out;
+		}
+
+		char vold[256], vnew[256];
+		if (zfs_tunable_get(tunable, vold, sizeof (vold)) != 0)
+			strcpy(vold, "???");
+		err = zfs_tunable_set(tunable, v);
+		if (err != 0)
+			goto out;
+		if (zfs_tunable_get(tunable, vnew, sizeof (vnew)) != 0)
+			strcpy(vnew, "???");
+
+		if (!quiet)
+			printf("%s: %s -> %s\n", k, vold, vnew);
+	} else if (k != NULL) {
+		const zfs_tunable_t *tunable = zfs_tunable_lookup(k);
+		if (tunable == NULL) {
+			err = ENOENT;
+			goto out;
+		}
+		list_tunables_cb(tunable, &mode);
+	} else {
+		zfs_tunable_iter(list_tunables_cb, &mode);
+	}
+
+out:
+	if (!quiet) {
+		if (err == ENOENT)
+			fprintf(stderr, "no such tunable: %s\n", k);
+		else if (err != 0)
+			fprintf(stderr, "couldn't set tunable '%s': %s\n",
+			    k, strerror(err));
+	}
+
+	free(arg);
+	return (err);
 }
 
 static nvlist_t *

man/man1/ztest.1

@@ -188,12 +188,8 @@ i.e. given
 will be loaded.
 .It Fl C , -vdev-class-state Ns = Ns Sy on Ns | Ns Sy off Ns | Ns Sy random No (default : Sy random  )
 The vdev allocation class state.
-.It Fl o , -option Ns = Ns Ar variable Ns = Ns Ar value
-Set global
-.Ar variable
-to an unsigned 32-bit integer
-.Ar value
-(little-endian only).
+.It Fl o , -option Ns = Ns Ar var Ns = Ns Ar value Ns …
+Set the given tunable to the provided value.
 .It Fl G , -dump-debug
 Dump zfs_dbgmsg buffer before exiting due to an error.
 .It Fl V , -verbose

man/man8/zdb.8

@@ -474,10 +474,15 @@ as it runs.
 Exercise extreme caution when using this option in shared or uncontrolled
 environments.
 .It Fl o , -option Ns = Ns Ar var Ns = Ns Ar value Ns …
-Set the given global libzpool variable to the provided value.
-The value must be an unsigned 32-bit integer.
-Currently only little-endian systems are supported to avoid accidentally setting
-the high 32 bits of 64-bit variables.
+Set the given tunable to the provided value.
+.It Fl o , -option Ns = Ns Ar var Ns …
+Show the value of the given tunable.
+.It Fl o , -option Ns = Ns show
+Show all tunables and their values.
+.It Fl o , -option Ns = Ns info Ns = Ns Ar value Ns …
+Show info about a tunable, including their name, type and description.
+.It Fl o , -option Ns = Ns info
+Show info about all tunables.
 .It Fl P , -parseable
 Print numbers in an unscaled form more amenable to parsing, e.g.\&
 .Sy 1000000