Implement -t option to zpool create for temporary pool names

Creating virtual machines that have their rootfs on ZFS on hosts that
have their rootfs on ZFS causes SPA namespace collisions when the
standard name rpool is used. The solution is either to give each guest
pool a name unique to the host, which is not always desireable, or boot
a VM environment containing an ISO image to install it, which is
cumbersome.

26b42f3 introduced `zpool import -t
...` to simplify situations where a host must access a guest's pool when
there is a SPA namespace conflict. We build upon that to introduce
`zpool import -t tname ...`. That allows us to create a pool whose
in-core name is tname, but whose on-disk name is the normal name
specified.

This simplifies the creation of machine images that use a rootfs on ZFS.
That benefits not only real world deployments, but also ZFSOnLinux
development by decreasing the time needed to perform rootfs on ZFS
experiments.

Signed-off-by: Richard Yao <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Issue openzfs#2417

cmd/zpool/zpool_main.c

@@ -822,7 +822,7 @@ zpool_do_create(int argc, char **argv)
 	char *propval;
 
 	/* check options */
-	while ((c = getopt(argc, argv, ":fndR:m:o:O:")) != -1) {
+	while ((c = getopt(argc, argv, ":fndR:m:o:O:t:")) != -1) {
 		switch (c) {
 		case 'f':
 			force = B_TRUE;
@@ -895,6 +895,26 @@ zpool_do_create(int argc, char **argv)
 				goto errout;
 			}
 			break;
+		case 't':
+			/*
+			 * Sanity check temporary pool name.
+			 */
+			if (strchr(optarg, '/') != NULL) {
+				(void) fprintf(stderr, gettext("cannot create "
+				    "'%s': invalid character '/' in temporary "
+				    "name\n"), optarg);
+				(void) fprintf(stderr, gettext("use 'zfs "
+				    "create' to create a dataset\n"));
+				goto errout;
+			}
+
+			if (add_prop_list(zpool_prop_to_name(
+			    ZPOOL_PROP_TNAME), optarg, &props, B_TRUE))
+				goto errout;
+			if (add_prop_list_default(zpool_prop_to_name(
+			    ZPOOL_PROP_CACHEFILE), "none", &props, B_TRUE))
+				goto errout;
+			break;
 		case ':':
 			(void) fprintf(stderr, gettext("missing argument for "
 			    "'%c' option\n"), optopt);

include/sys/fs/zfs.h

@@ -196,6 +196,7 @@ typedef enum {
 	ZPOOL_PROP_FREEING,
 	ZPOOL_PROP_FRAGMENTATION,
 	ZPOOL_PROP_LEAKED,
+	ZPOOL_PROP_TNAME,
 	ZPOOL_NUM_PROPS
 } zpool_prop_t;
 

lib/libzfs/libzfs_pool.c

@@ -710,6 +710,15 @@ zpool_valid_proplist(libzfs_handle_t *hdl, const char *poolname,
 				goto error;
 			}
 			break;
+		case ZPOOL_PROP_TNAME:
+			if (!flags.create) {
+				zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
+				    "property '%s' can only be set at "
+				    "creation time"), propname);
+				(void) zfs_error(hdl, EZFS_BADPROP, errbuf);
+				goto error;
+			}
+			break;
 		}
 	}
 

man/man8/zpool.8

@@ -42,7 +42,7 @@ zpool \- configures ZFS storage pools
 .LP
 .nf
 \fBzpool create\fR [\fB-fnd\fR] [\fB-o\fR \fIproperty=value\fR] ... [\fB-O\fR \fIfile-system-property=value\fR]
-     ... [\fB-m\fR \fImountpoint\fR] [\fB-R\fR \fIroot\fR] \fIpool\fR \fIvdev\fR ...
+     ... [\fB-m\fR \fImountpoint\fR] [\fB-R\fR \fIroot\fR] [\fB-t\fR \fItname\fR] \fIpool\fR \fIvdev\fR ...
 .fi
 
 .LP
@@ -920,7 +920,7 @@ Clears device errors in a pool. If no arguments are specified, all device errors
 .ne 2
 .mk
 .na
-\fB\fBzpool create\fR [\fB-fnd\fR] [\fB-o\fR \fIproperty=value\fR] ... [\fB-O\fR \fIfile-system-property=value\fR] ... [\fB-m\fR \fImountpoint\fR] [\fB-R\fR \fIroot\fR] \fIpool\fR \fIvdev\fR ...\fR
+\fB\fBzpool create\fR [\fB-fnd\fR] [\fB-o\fR \fIproperty=value\fR] ... [\fB-O\fR \fIfile-system-property=value\fR] ... [\fB-m\fR \fImountpoint\fR] [\fB-R\fR \fIroot\fR] [\fB-t\fR \fItname\fR] \fIpool\fR \fIvdev\fR ...\fR
 .ad
 .sp .6
 .RS 4n
@@ -1013,6 +1013,17 @@ Equivalent to "-o cachefile=none,altroot=\fIroot\fR"
 Sets the mount point for the root dataset. The default mount point is "/\fIpool\fR" or "\fBaltroot\fR/\fIpool\fR" if \fBaltroot\fR is specified. The mount point must be an absolute path, "\fBlegacy\fR", or "\fBnone\fR". For more information on dataset mount points, see \fBzfs\fR(8).
 .RE
 
+.sp
+.ne 2
+.mk
+.na
+\fB\fB-t\fR \fItname\fR\fR
+.ad
+.sp .6
+.RS 4n
+Sets the in-core pool name to "\fBtname\fR" while the on-disk name will be the name specified as the pool name "\fBpool\fR". This will set the default cachefile property to none. This is intended to handle name space collisions when creating pools for other systems, such as virtual machines or physical machines whose pools live on network block devices.
+.RE
+
 .RE
 
 .sp

module/zcommon/zpool_prop.c

@@ -131,6 +131,8 @@ zpool_prop_init(void)
 	/* hidden properties */
 	zprop_register_hidden(ZPOOL_PROP_NAME, "name", PROP_TYPE_STRING,
 	    PROP_READONLY, ZFS_TYPE_POOL, "NAME");
+	zprop_register_hidden(ZPOOL_PROP_TNAME, "tname", PROP_TYPE_STRING,
+	    PROP_ONETIME, ZFS_TYPE_POOL, "TNAME");
 }
 
 /*

module/zfs/spa.c

@@ -3496,22 +3496,30 @@ spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
 	boolean_t has_features;
 	nvpair_t *elem;
 	int c;
+	char *poolname;
+	nvlist_t *nvl;
+
+	if (nvlist_lookup_string(props, "tname", &poolname) != 0)
+		poolname = (char *)pool;
 
 	/*
 	 * If this pool already exists, return failure.
 	 */
 	mutex_enter(&spa_namespace_lock);
-	if (spa_lookup(pool) != NULL) {
+	if (spa_lookup(poolname) != NULL) {
 		mutex_exit(&spa_namespace_lock);
 		return (SET_ERROR(EEXIST));
 	}
 
 	/*
 	 * Allocate a new spa_t structure.
 	 */
+	nvl = fnvlist_alloc();
+	fnvlist_add_string(nvl, ZPOOL_CONFIG_POOL_NAME, pool);
 	(void) nvlist_lookup_string(props,
 	    zpool_prop_to_name(ZPOOL_PROP_ALTROOT), &altroot);
-	spa = spa_add(pool, NULL, altroot);
+	spa = spa_add(poolname, nvl, altroot);
+	fnvlist_free(nvl);
 	spa_activate(spa, spa_mode_global);
 
 	if (props && (error = spa_prop_validate(spa, props))) {
@@ -3521,6 +3529,12 @@ spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
 		return (error);
 	}
 
+	/*
+	 * Temporary pool names should never be written to disk.
+	 */
+	if (poolname != pool)
+		spa->spa_import_flags |= ZFS_IMPORT_TEMP_NAME;
+
 	has_features = B_FALSE;
 	for (elem = nvlist_next_nvpair(props, NULL);
 	    elem != NULL; elem = nvlist_next_nvpair(props, elem)) {