Implement -t option to zpool import for temporary pool names

Originally, users had to handle spa namespace collisions by either
exporting the already imported pool or by specifying a new name for the
pool with a conflicting name. In the case of root pools from virtual
guests, neither approach to collision resolution is reasonable. This is
addressed by extending the new name syntax with a -t option to specify
that the new name is temporary. When specified, this sets an internal
flag that is passed into the kernel to tell it that all label updates
should refer to the name used in the original label. Consequently, the
original pool name will be retained on export.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2189

cmd/zpool/zpool_main.c

@@ -2013,7 +2013,7 @@ zpool_do_import(int argc, char **argv)
 	char *endptr;
 
 	/* check options */
-	while ((c = getopt(argc, argv, ":aCc:d:DEfFmnNo:R:T:VX")) != -1) {
+	while ((c = getopt(argc, argv, ":aCc:d:DEfFmnNo:R:tT:VX")) != -1) {
 		switch (c) {
 		case 'a':
 			do_all = B_TRUE;
@@ -2075,6 +2075,10 @@ zpool_do_import(int argc, char **argv)
 			    ZPOOL_PROP_CACHEFILE), "none", &props, B_TRUE))
 				goto error;
 			break;
+		case 't':
+			flags |= ZFS_IMPORT_TEMP_NAME;
+			break;
+
 		case 'T':
 			errno = 0;
 			txg = strtoull(optarg, &endptr, 10);

include/sys/fs/zfs.h

@@ -936,6 +936,7 @@ typedef enum {
 #define	ZFS_IMPORT_ANY_HOST	0x2
 #define	ZFS_IMPORT_MISSING_LOG	0x4
 #define	ZFS_IMPORT_ONLY		0x8
+#define	ZFS_IMPORT_TEMP_NAME	0x10
 
 /*
  * Sysevent payload members.  ZFS will generate the following sysevents with the

man/man8/zpool.8

@@ -84,7 +84,7 @@ zpool \- configures ZFS storage pools
 .LP
 .nf
 \fBzpool import\fR [\fB-o \fImntopts\fR\fR] [\fB-o\fR \fIproperty=value\fR] ... [\fB-d\fR \fIdir\fR | \fB-c\fR \fIcachefile\fR]
-     [\fB-D\fR] [\fB-f\fR] [\fB-m\fR] [\fB-R\fR \fIroot\fR] [\fB-F\fR [\fB-n\fR]] \fIpool\fR |\fIid\fR [\fInewpool\fR]
+     [\fB-D\fR] [\fB-f\fR] [\fB-m\fR] [\fB-R\fR \fIroot\fR] [\fB-F\fR [\fB-n\fR]] [\fB-t\fR]] \fIpool\fR |\fIid\fR [\fInewpool\fR]
 .fi
 
 .LP
@@ -1300,7 +1300,7 @@ Used with the \fB-F\fR recovery option. Determines whether a non-importable pool
 .ne 2
 .mk
 .na
-\fB\fBzpool import\fR [\fB-o\fR \fImntopts\fR] [ \fB-o\fR \fIproperty\fR=\fIvalue\fR] ... [\fB-d\fR \fIdir\fR | \fB-c\fR \fIcachefile\fR] [\fB-D\fR] [\fB-f\fR] [\fB-m\fR] [\fB-R\fR \fIroot\fR] [\fB-F\fR [\fB-n\fR]] \fIpool\fR | \fIid\fR [\fInewpool\fR]\fR
+\fB\fBzpool import\fR [\fB-o\fR \fImntopts\fR] [ \fB-o\fR \fIproperty\fR=\fIvalue\fR] ... [\fB-d\fR \fIdir\fR | \fB-c\fR \fIcachefile\fR] [\fB-D\fR] [\fB-f\fR] [\fB-m\fR] [\fB-R\fR \fIroot\fR] [\fB-F\fR [\fB-n\fR]] [\fB-t\fR]] \fIpool\fR | \fIid\fR [\fInewpool\fR]\fR
 .ad
 .sp .6
 .RS 4n
@@ -1406,6 +1406,17 @@ Sets the "\fBcachefile\fR" property to "\fBnone\fR" and the "\fIaltroot\fR" prop
 Used with the \fB-F\fR recovery option. Determines whether a non-importable pool can be made importable again, but does not actually perform the pool recovery. For more details about pool recovery mode, see the \fB-F\fR option, above.
 .RE
 
+.sp
+.ne 2
+.mk
+.na
+\fB\fB-t\fR\fR
+.ad
+.sp .6
+.RS 4n
+Used with "\fBnewpool\fR". Specifies that "\fBnewpool\fR" is temporary. Temporary pool names last until export. Ensures that the original pool name will be used in all label updates and therefore is retained upon export.
+.RE
+
 .sp
 .ne 2
 .mk

module/zfs/spa_config.c

@@ -208,6 +208,7 @@ spa_config_sync(spa_t *target, boolean_t removing, boolean_t postsysevent)
 {
 	spa_config_dirent_t *dp, *tdp;
 	nvlist_t *nvl;
+	char *pool_name;
 
 	ASSERT(MUTEX_HELD(&spa_namespace_lock));
 
@@ -254,7 +255,13 @@ spa_config_sync(spa_t *target, boolean_t removing, boolean_t postsysevent)
 				VERIFY(nvlist_alloc(&nvl, NV_UNIQUE_NAME,
 				    KM_PUSHPAGE) == 0);
 
-			VERIFY(nvlist_add_nvlist(nvl, spa->spa_name,
+			if (spa->spa_import_flags & ZFS_IMPORT_TEMP_NAME) {
+				VERIFY0(nvlist_lookup_string(spa->spa_config,
+					ZPOOL_CONFIG_POOL_NAME, &pool_name));
+			} else
+				pool_name = spa_name(spa);
+
+			VERIFY(nvlist_add_nvlist(nvl, pool_name,
 			    spa->spa_config) == 0);
 			mutex_exit(&spa->spa_props_lock);
 		}
@@ -337,6 +344,7 @@ spa_config_generate(spa_t *spa, vdev_t *vd, uint64_t txg, int getstats)
 	unsigned long hostid = 0;
 	boolean_t locked = B_FALSE;
 	uint64_t split_guid;
+	char *pool_name;
 
 	if (vd == NULL) {
 		vd = rvd;
@@ -353,12 +361,28 @@ spa_config_generate(spa_t *spa, vdev_t *vd, uint64_t txg, int getstats)
 	if (txg == -1ULL)
 		txg = spa->spa_config_txg;
 
+	/*
+	 * Originally, users had to handle spa namespace collisions by either
+	 * exporting the already imported pool or by specifying a new name for
+	 * the pool with a conflicting name. In the case of root pools from
+	 * virtual guests, neither approach to collision resolution is
+	 * reasonable. This is addressed by extending the new name syntax with
+	 * an option to specify that the new name is temporary. When specified,
+	 * ZFS_IMPORT_TEMP_NAME will be set in spa->spa_import_flags to tell us
+	 * to use the previous name, which we do below.
+	 */
+	if (spa->spa_import_flags & ZFS_IMPORT_TEMP_NAME) {
+		VERIFY0(nvlist_lookup_string(spa->spa_config,
+			ZPOOL_CONFIG_POOL_NAME, &pool_name));
+	} else
+		pool_name = spa_name(spa);
+
 	VERIFY(nvlist_alloc(&config, NV_UNIQUE_NAME, KM_PUSHPAGE) == 0);
 
 	VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_VERSION,
 	    spa_version(spa)) == 0);
 	VERIFY(nvlist_add_string(config, ZPOOL_CONFIG_POOL_NAME,
-	    spa_name(spa)) == 0);
+	    pool_name) == 0);
 	VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_POOL_STATE,
 	    spa_state(spa)) == 0);
 	VERIFY(nvlist_add_uint64(config, ZPOOL_CONFIG_POOL_TXG,