Add zfs_prepare_disk script for disk firmware install

Have libzfs call a special `zfs_prepare_disk` script before a disk is
included into the pool.  The user can edit this script to add things
like a disk firmware update or a disk health check.  Use of the script
is totally optional. See the zfs_prepare_disk manpage for full details.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #15243

cmd/zed/agents/zfs_mod.c

@@ -141,6 +141,17 @@ zfs_unavail_pool(zpool_handle_t *zhp, void *data)
 	return (0);
 }
 
+/*
+ * Write an array of strings to the zed log
+ */
+static void lines_to_zed_log_msg(char **lines, int lines_cnt)
+{
+	int i;
+	for (i = 0; i < lines_cnt; i++) {
+		zed_log_msg(LOG_INFO, "%s", lines[i]);
+	}
+}
+
 /*
  * Two stage replace on Linux
  * since we get disk notifications
@@ -195,6 +206,8 @@ zfs_process_add(zpool_handle_t *zhp, nvlist_t *vdev, boolean_t labeled)
 	boolean_t is_mpath_wholedisk = B_FALSE;
 	uint_t c;
 	vdev_stat_t *vs;
+	char **lines = NULL;
+	int lines_cnt = 0;
 
 	if (nvlist_lookup_string(vdev, ZPOOL_CONFIG_PATH, &path) != 0)
 		return;
@@ -377,6 +390,22 @@ zfs_process_add(zpool_handle_t *zhp, nvlist_t *vdev, boolean_t labeled)
 
 	if (is_mpath_wholedisk) {
 		/* Don't label device mapper or multipath disks. */
+		zed_log_msg(LOG_INFO,
+		    "  it's a multipath wholedisk, don't label");
+		if (zpool_prepare_disk(zhp, vdev, "autoreplace", &lines,
+		    &lines_cnt) != 0) {
+			zed_log_msg(LOG_INFO,
+			    "  zpool_prepare_disk: could not "
+			    "prepare '%s' (%s)", fullpath,
+			    libzfs_error_description(g_zfshdl));
+			if (lines_cnt > 0) {
+				zed_log_msg(LOG_INFO,
+				    "  zfs_prepare_disk output:");
+				lines_to_zed_log_msg(lines, lines_cnt);
+			}
+			libzfs_free_str_array(lines, lines_cnt);
+			return;
+		}
 	} else if (!labeled) {
 		/*
 		 * we're auto-replacing a raw disk, so label it first
@@ -399,10 +428,18 @@ zfs_process_add(zpool_handle_t *zhp, nvlist_t *vdev, boolean_t labeled)
 		 * If this is a request to label a whole disk, then attempt to
 		 * write out the label.
 		 */
-		if (zpool_label_disk(g_zfshdl, zhp, leafname) != 0) {
-			zed_log_msg(LOG_INFO, "  zpool_label_disk: could not "
+		if (zpool_prepare_and_label_disk(g_zfshdl, zhp, leafname,
+		    vdev, "autoreplace", &lines, &lines_cnt) != 0) {
+			zed_log_msg(LOG_INFO,
+			    "  zpool_prepare_and_label_disk: could not "
 			    "label '%s' (%s)", leafname,
 			    libzfs_error_description(g_zfshdl));
+			if (lines_cnt > 0) {
+				zed_log_msg(LOG_INFO,
+				"  zfs_prepare_disk output:");
+				lines_to_zed_log_msg(lines, lines_cnt);
+			}
+			libzfs_free_str_array(lines, lines_cnt);
 
 			(void) zpool_vdev_online(zhp, fullpath,
 			    ZFS_ONLINE_FORCEFAULT, &newstate);
@@ -457,6 +494,8 @@ zfs_process_add(zpool_handle_t *zhp, nvlist_t *vdev, boolean_t labeled)
 		    DEV_BYID_PATH, new_devid);
 	}
 
+	libzfs_free_str_array(lines, lines_cnt);
+
 	/*
 	 * Construct the root vdev to pass to zpool_vdev_attach().  While adding
 	 * the entire vdev structure is harmless, we construct a reduced set of

cmd/zpool/zpool_iter.c

@@ -439,39 +439,23 @@ 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;
 	char **lines = NULL;
 	int lines_cnt = 0;
 	int i;
 
-	/* Setup our custom environment variables */
-	rc = asprintf(&env[1], "VDEV_PATH=%s",
-	    data->path ? data->path : "");
-	if (rc == -1) {
-		env[1] = NULL;
+	env = zpool_vdev_script_alloc_env(data->pool, data->path, data->upath,
+	    data->vdev_enc_sysfs_path, NULL, NULL);
+	if (env == NULL)
 		goto out;
-	}
-
-	rc = asprintf(&env[2], "VDEV_UPATH=%s",
-	    data->upath ? data->upath : "");
-	if (rc == -1) {
-		env[2] = NULL;
-		goto out;
-	}
-
-	rc = asprintf(&env[3], "VDEV_ENC_SYSFS_PATH=%s",
-	    data->vdev_enc_sysfs_path ?
-	    data->vdev_enc_sysfs_path : "");
-	if (rc == -1) {
-		env[3] = NULL;
-		goto out;
-	}
 
 	/* Run the command */
 	rc = libzfs_run_process_get_stdout_nopath(cmd, argv, env, &lines,
 	    &lines_cnt);
+
+	zpool_vdev_script_free_env(env);
+
 	if (rc != 0)
 		goto out;
 
@@ -483,10 +467,6 @@ vdev_run_cmd(vdev_cmd_data_t *data, char *cmd)
 out:
 	if (lines != NULL)
 		libzfs_free_str_array(lines, lines_cnt);
-
-	/* Start with i = 1 since env[0] was statically allocated */
-	for (i = 1; i < ARRAY_SIZE(env); i++)
-		free(env[i]);
 }
 
 /*

cmd/zpool/zpool_util.h

@@ -124,6 +124,10 @@ vdev_cmd_data_list_t *all_pools_for_each_vdev_run(int argc, char **argv,
 
 void free_vdev_cmd_data_list(vdev_cmd_data_list_t *vcdl);
 
+void free_vdev_cmd_data(vdev_cmd_data_t *data);
+
+int vdev_run_cmd_simple(char *path, char *cmd);
+
 int check_device(const char *path, boolean_t force,
     boolean_t isspare, boolean_t iswholedisk);
 boolean_t check_sector_size_database(char *path, int *sector_size);

cmd/zpool/zpool_vdev.c

@@ -921,6 +921,15 @@ zero_label(char *path)
 	return (0);
 }
 
+static void
+lines_to_stderr(char *lines[], int lines_cnt)
+{
+	int i;
+	for (i = 0; i < lines_cnt; i++) {
+		fprintf(stderr, "%s\n", lines[i]);
+	}
+}
+
 /*
  * Go through and find any whole disks in the vdev specification, labelling them
  * as appropriate.  When constructing the vdev spec, we were unable to open this
@@ -932,7 +941,7 @@ zero_label(char *path)
  * need to get the devid after we label the disk.
  */
 static int
-make_disks(zpool_handle_t *zhp, nvlist_t *nv)
+make_disks(zpool_handle_t *zhp, nvlist_t *nv, boolean_t replacing)
 {
 	nvlist_t **child;
 	uint_t c, children;
@@ -1017,6 +1026,8 @@ make_disks(zpool_handle_t *zhp, nvlist_t *nv)
 		 */
 		if (!is_exclusive && !is_spare(NULL, udevpath)) {
 			char *devnode = strrchr(devpath, '/') + 1;
+			char **lines = NULL;
+			int lines_cnt = 0;
 
 			ret = strncmp(udevpath, UDISK_ROOT, strlen(UDISK_ROOT));
 			if (ret == 0) {
@@ -1028,9 +1039,27 @@ make_disks(zpool_handle_t *zhp, nvlist_t *nv)
 			/*
 			 * When labeling a pool the raw device node name
 			 * is provided as it appears under /dev/.
+			 *
+			 * Note that 'zhp' will be NULL when we're creating a
+			 * pool.
 			 */
-			if (zpool_label_disk(g_zfs, zhp, devnode) == -1)
+			if (zpool_prepare_and_label_disk(g_zfs, zhp, devnode,
+			    nv, zhp == NULL ? "create" :
+			    replacing ? "replace" : "add", &lines,
+			    &lines_cnt) != 0) {
+				(void) fprintf(stderr,
+				    gettext(
+				    "Error preparing/labeling disk.\n"));
+				if (lines_cnt > 0) {
+					(void) fprintf(stderr,
+					gettext("zfs_prepare_disk output:\n"));
+					lines_to_stderr(lines, lines_cnt);
+				}
+
+				libzfs_free_str_array(lines, lines_cnt);
 				return (-1);
+			}
+			libzfs_free_str_array(lines, lines_cnt);
 
 			/*
 			 * Wait for udev to signal the device is available
@@ -1067,19 +1096,19 @@ make_disks(zpool_handle_t *zhp, nvlist_t *nv)
 	}
 
 	for (c = 0; c < children; c++)
-		if ((ret = make_disks(zhp, child[c])) != 0)
+		if ((ret = make_disks(zhp, child[c], replacing)) != 0)
 			return (ret);
 
 	if (nvlist_lookup_nvlist_array(nv, ZPOOL_CONFIG_SPARES,
 	    &child, &children) == 0)
 		for (c = 0; c < children; c++)
-			if ((ret = make_disks(zhp, child[c])) != 0)
+			if ((ret = make_disks(zhp, child[c], replacing)) != 0)
 				return (ret);
 
 	if (nvlist_lookup_nvlist_array(nv, ZPOOL_CONFIG_L2CACHE,
 	    &child, &children) == 0)
 		for (c = 0; c < children; c++)
-			if ((ret = make_disks(zhp, child[c])) != 0)
+			if ((ret = make_disks(zhp, child[c], replacing)) != 0)
 				return (ret);
 
 	return (0);
@@ -1740,7 +1769,7 @@ split_mirror_vdev(zpool_handle_t *zhp, char *newname, nvlist_t *props,
 			return (NULL);
 		}
 
-		if (!flags.dryrun && make_disks(zhp, newroot) != 0) {
+		if (!flags.dryrun && make_disks(zhp, newroot, B_FALSE) != 0) {
 			nvlist_free(newroot);
 			return (NULL);
 		}
@@ -1861,7 +1890,7 @@ make_root_vdev(zpool_handle_t *zhp, nvlist_t *props, int force, int check_rep,
 	/*
 	 * Run through the vdev specification and label any whole disks found.
 	 */
-	if (!dryrun && make_disks(zhp, newroot) != 0) {
+	if (!dryrun && make_disks(zhp, newroot, replacing) != 0) {
 		nvlist_free(newroot);
 		return (NULL);
 	}

config/Rules.am

@@ -41,6 +41,7 @@ AM_CPPFLAGS += -D_REENTRANT
 AM_CPPFLAGS += -D_FILE_OFFSET_BITS=64
 AM_CPPFLAGS += -D_LARGEFILE64_SOURCE
 AM_CPPFLAGS += -DLIBEXECDIR=\"$(libexecdir)\"
+AM_CPPFLAGS += -DZFSEXECDIR=\"$(zfsexecdir)\"
 AM_CPPFLAGS += -DRUNSTATEDIR=\"$(runstatedir)\"
 AM_CPPFLAGS += -DSBINDIR=\"$(sbindir)\"
 AM_CPPFLAGS += -DSYSCONFDIR=\"$(sysconfdir)\"

include/libzfs.h

@@ -318,6 +318,15 @@ extern nvlist_t *zpool_find_vdev(zpool_handle_t *, const char *, boolean_t *,
 extern nvlist_t *zpool_find_vdev_by_physpath(zpool_handle_t *, const char *,
     boolean_t *, boolean_t *, boolean_t *);
 extern int zpool_label_disk(libzfs_handle_t *, zpool_handle_t *, const char *);
+extern int zpool_prepare_disk(zpool_handle_t *zhp, nvlist_t *vdev_nv,
+    const char *prepare_str, char **lines[], int *lines_cnt);
+extern int zpool_prepare_and_label_disk(libzfs_handle_t *hdl,
+    zpool_handle_t *, const char *, nvlist_t *vdev_nv, const char *prepare_str,
+    char **lines[], int *lines_cnt);
+extern char ** zpool_vdev_script_alloc_env(const char *pool_name,
+    const char *vdev_path, const char *vdev_upath,
+    const char *vdev_enc_sysfs_path, const char *opt_key, const char *opt_val);
+extern void zpool_vdev_script_free_env(char **env);
 extern uint64_t zpool_vdev_path_to_guid(zpool_handle_t *zhp, const char *path);
 
 const char *zpool_get_state_str(zpool_handle_t *);

lib/libzfs/libzfs.abi

@@ -333,6 +333,8 @@
     <elf-symbol name='zpool_open_canfail' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='zpool_open_silent' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='zpool_pool_state_to_name' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='zpool_prepare_and_label_disk' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='zpool_prepare_disk' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='zpool_print_unsup_feat' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='zpool_prop_align_right' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='zpool_prop_column_name' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
@@ -380,6 +382,8 @@
     <elf-symbol name='zpool_vdev_remove' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='zpool_vdev_remove_cancel' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='zpool_vdev_remove_wanted' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='zpool_vdev_script_alloc_env' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
+    <elf-symbol name='zpool_vdev_script_free_env' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='zpool_vdev_split' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='zpool_wait' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>
     <elf-symbol name='zpool_wait_status' type='func-type' binding='global-binding' visibility='default-visibility' is-defined='yes'/>

lib/libzfs/libzfs_util.c

@@ -2121,3 +2121,196 @@ printf_color(const char *color, char *format, ...)
 
 	return (rc);
 }
+
+/* PATH + 5 env vars + a NULL entry = 7 */
+#define	ZPOOL_VDEV_SCRIPT_ENV_COUNT 7
+
+/*
+ * There's a few places where ZFS will call external scripts (like the script
+ * in zpool.d/ and `zfs_prepare_disk`).  These scripts are called with a
+ * reduced $PATH, and some vdev specific environment vars set.  This function
+ * will allocate an populate the environment variable array that is passed to
+ * these scripts.  The user must free the arrays with zpool_vdev_free_env() when
+ * they are done.
+ *
+ * The following env vars will be set (but value could be blank):
+ *
+ * POOL_NAME
+ * VDEV_PATH
+ * VDEV_UPATH
+ * VDEV_ENC_SYSFS_PATH
+ *
+ * In addition, you can set an optional environment variable named 'opt_key'
+ * to 'opt_val' if you want.
+ *
+ * Returns allocated env[] array on success, NULL otherwise.
+ */
+char **
+zpool_vdev_script_alloc_env(const char *pool_name,
+    const char *vdev_path, const char *vdev_upath,
+    const char *vdev_enc_sysfs_path, const char *opt_key, const char *opt_val)
+{
+	char **env = NULL;
+	int rc;
+
+	env = calloc(ZPOOL_VDEV_SCRIPT_ENV_COUNT, sizeof (*env));
+	if (!env)
+		return (NULL);
+
+	env[0] = strdup("PATH=/bin:/sbin:/usr/bin:/usr/sbin");
+	if (!env[0])
+		goto error;
+
+	/* Setup our custom environment variables */
+	rc = asprintf(&env[1], "POOL_NAME=%s", pool_name ? pool_name : "");
+	if (rc == -1) {
+		env[1] = NULL;
+		goto error;
+	}
+
+	rc = asprintf(&env[2], "VDEV_PATH=%s", vdev_path ? vdev_path : "");
+	if (rc == -1) {
+		env[2] = NULL;
+		goto error;
+	}
+
+	rc = asprintf(&env[3], "VDEV_UPATH=%s", vdev_upath ? vdev_upath : "");
+	if (rc == -1) {
+		env[3] = NULL;
+		goto error;
+	}
+
+	rc = asprintf(&env[4], "VDEV_ENC_SYSFS_PATH=%s",
+	    vdev_enc_sysfs_path ?  vdev_enc_sysfs_path : "");
+	if (rc == -1) {
+		env[4] = NULL;
+		goto error;
+	}
+
+	if (opt_key != NULL) {
+		rc = asprintf(&env[5], "%s=%s", opt_key,
+		    opt_val ? opt_val : "");
+		if (rc == -1) {
+			env[5] = NULL;
+			goto error;
+		}
+	}
+
+	return (env);
+
+error:
+	for (int i = 0; i < ZPOOL_VDEV_SCRIPT_ENV_COUNT; i++)
+		free(env[i]);
+
+	free(env);
+
+	return (NULL);
+}
+
+/*
+ * Free the env[] array that was allocated by zpool_vdev_script_alloc_env().
+ */
+void
+zpool_vdev_script_free_env(char **env)
+{
+	for (int i = 0; i < ZPOOL_VDEV_SCRIPT_ENV_COUNT; i++)
+		free(env[i]);
+
+	free(env);
+}
+
+/*
+ * Prepare a disk by (optionally) running a program before labeling the disk.
+ * This can be useful for installing disk firmware or doing some pre-flight
+ * checks on the disk before it becomes part of the pool.  The program run is
+ * located at ZFSEXECDIR/zfs_prepare_disk
+ * (E.x: /usr/local/libexec/zfs/zfs_prepare_disk).
+ *
+ * Return 0 on success, non-zero on failure.
+ */
+int
+zpool_prepare_disk(zpool_handle_t *zhp, nvlist_t *vdev_nv,
+    const char *prepare_str, char **lines[], int *lines_cnt)
+{
+	const char *script_path = ZFSEXECDIR "/zfs_prepare_disk";
+	const char *pool_name;
+	int rc = 0;
+
+	/* Path to script and a NULL entry */
+	char *argv[2] = {(char *)script_path};
+	char **env = NULL;
+	char *path = NULL, *enc_sysfs_path = NULL;
+	char *upath;
+	*lines_cnt = 0;
+
+	if (access(script_path, X_OK) != 0) {
+		/* No script, nothing to do */
+		return (0);
+	}
+
+	(void) nvlist_lookup_string(vdev_nv, ZPOOL_CONFIG_PATH, &path);
+	(void) nvlist_lookup_string(vdev_nv, ZPOOL_CONFIG_VDEV_ENC_SYSFS_PATH,
+	    &enc_sysfs_path);
+
+	upath = zfs_get_underlying_path(path);
+	pool_name = zhp ? zpool_get_name(zhp) : NULL;
+
+	env = zpool_vdev_script_alloc_env(pool_name, path, upath,
+	    enc_sysfs_path, "VDEV_PREPARE", prepare_str);
+
+	free(upath);
+
+	if (env == NULL) {
+		return (ENOMEM);
+	}
+
+	rc = libzfs_run_process_get_stdout(script_path, argv, env, lines,
+	    lines_cnt);
+
+	zpool_vdev_script_free_env(env);
+
+	return (rc);
+}
+
+/*
+ * Optionally run a script and then label a disk.  The script can be used to
+ * prepare a disk for inclusion into the pool.  For example, it might update
+ * the disk's firmware or check its health.
+ *
+ * The 'name' provided is the short name, stripped of any leading
+ * /dev path, and is passed to zpool_label_disk. vdev_nv is the nvlist for
+ * the vdev.  prepare_str is a string that gets passed as the VDEV_PREPARE
+ * env variable to the script.
+ *
+ * The following env vars are passed to the script:
+ *
+ * POOL_NAME:		The pool name (blank during zpool create)
+ * VDEV_PREPARE:	Reason why the disk is being prepared for inclusion:
+ *			"create", "add", "replace", or "autoreplace"
+ * VDEV_PATH:		Path to the disk
+ * VDEV_UPATH:		One of the 'underlying paths' to the disk.  This is
+ * 			useful for DM devices.
+ * VDEV_ENC_SYSFS_PATH:	Path to the disk's enclosure sysfs path, if available.
+ *
+ * Note, some of these values can be blank.
+ *
+ * Return 0 on success, non-zero otherwise.
+ */
+int
+zpool_prepare_and_label_disk(libzfs_handle_t *hdl, zpool_handle_t *zhp,
+    const char *name, nvlist_t *vdev_nv, const char *prepare_str,
+    char **lines[], int *lines_cnt)
+{
+	int rc;
+	char vdev_path[MAXPATHLEN];
+	(void) snprintf(vdev_path, sizeof (vdev_path), "%s/%s", DISK_ROOT,
+	    name);
+
+	/* zhp will be NULL when creating a pool */
+	rc = zpool_prepare_disk(zhp, vdev_nv, prepare_str, lines, lines_cnt);
+	if (rc != 0)
+		return (rc);
+
+	rc = zpool_label_disk(hdl, zhp, name);
+	return (rc);
+}

man/Makefile.am

@@ -104,7 +104,8 @@ dist_man_MANS = \
 
 nodist_man_MANS = \
 	man8/zed.8 \
-	man8/zfs-mount-generator.8
+	man8/zfs-mount-generator.8 \
+	man8/zfs_prepare_disk.8
 
 SUBSTFILES += $(nodist_man_MANS)
 

man/man8/.gitignore

@@ -1,2 +1,3 @@
 /zed.8
 /zfs-mount-generator.8
+/zfs_prepare_disk.8

man/man8/zfs_prepare_disk.8.in

@@ -0,0 +1,70 @@
+.\"
+.\" Developed at Lawrence Livermore National Laboratory (LLNL-CODE-403049).
+.\" Copyright (C) 2023 Lawrence Livermore National Security, LLC.
+.\" Refer to the OpenZFS git commit log for authoritative copyright attribution.
+.\"
+.\" The contents of this file are subject to the terms of the
+.\" Common Development and Distribution License Version 1.0 (CDDL-1.0).
+.\" You can obtain a copy of the license from the top-level file
+.\" "OPENSOLARIS.LICENSE" or at <http://opensource.org/licenses/CDDL-1.0>.
+.\" You may not use this file except in compliance with the license.
+.\"
+.\" Developed at Lawrence Livermore National Laboratory (LLNL-CODE-403049)
+.\"
+.Dd August 30, 2023
+.Dt ZFS_PREPARE_DISK 8
+.Os
+.
+.Sh NAME
+.Nm zfs_prepare_disk
+.Nd special script that gets run before bringing a disk into a pool
+.Sh DESCRIPTION
+.Nm
+is an optional script that gets called by libzfs before bringing a disk into a
+pool.
+It can be modified by the user to run whatever commands are necessary to prepare
+a disk for inclusion into the pool.
+For example, users can add lines to
+.Nm zfs_prepare_disk
+to do things like update the drive's firmware or check the drive's health.
+.Nm zfs_prepare_disk
+is optional and can be removed if not needed.
+libzfs will look for the script at @zfsexecdir@/zfs_prepare_disk.
+.
+.Ss Properties
+.Nm zfs_prepare_disk
+will be passed the following environment variables:
+.sp
+.Bl -tag -compact -width "VDEV_ENC_SYSFS_PATH"
+.
+.It Nm POOL_NAME
+.No Name of the pool
+.It Nm VDEV_PATH
+.No Path to the disk (like /dev/sda)
+.It Nm VDEV_PREPARE
+.No Reason why the disk is being prepared for inclusion
+('create', 'add', 'replace', or 'autoreplace').
+This can be useful if you only want the script to be run under certain actions.
+.It Nm VDEV_UPATH
+.No Path to one of the underlying devices for the
+disk.
+For multipath this would return one of the /dev/sd* paths to the disk.
+If the device is not a device mapper device, then
+.Nm VDEV_UPATH
+just returns the same value as
+.Nm VDEV_PATH
+.It Nm VDEV_ENC_SYSFS_PATH
+.No Path to the disk's enclosure sysfs path, if available
+.El
+.Pp
+Note that some of these variables may have a blank value.
+.Nm POOL_NAME
+is blank at pool creation time, for example.
+.Sh ENVIRONMENT
+.Nm zfs_prepare_disk
+runs with a limited $PATH.
+.Sh EXIT STATUS
+.Nm zfs_prepare_disk
+should return 0 on success, non-zero otherwise.
+If non-zero is returned, the disk will not be included in the pool.
+.

scripts/Makefile.am

@@ -9,6 +9,9 @@ dist_pkgdata_SCRIPTS = \
 	zloop.sh \
 	zfs-helpers.sh
 
+dist_zfsexec_SCRIPTS = \
+	zfs_prepare_disk
+
 EXTRA_SCRIPTS = \
 	commitcheck.sh \
 	common.sh.in \

scripts/zfs_prepare_disk

@@ -0,0 +1,17 @@
+#!/bin/sh
+#
+# This is an optional helper script that is automatically called by libzfs
+# before a disk is about to be added into the pool.  It can be modified by
+# the user to run whatever commands are necessary to prepare a disk for
+# inclusion into the pool.  For example, users can add lines to this
+# script to do things like update the drive's firmware or check the drive's
+# health.  The script is optional and can be removed if it is not needed.
+#
+# See the zfs_prepare_disk(8) man page for details.
+#
+# Example:
+#
+# echo "Prepare disk $VDEV_PATH ($VDEV_UPATH) for $VDEV_PREPARE in $POOL_NAME"
+#
+
+exit 0