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 <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #2189

4 files changed, 45 insertions, 5 deletions

diff --git a/cmd/zpool/zpool_main.c b/cmd/zpool/zpool_main.c
index 1c606e077..d095b15a5 100644
--- a/cmd/zpool/zpool_main.c
+++ b/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);
diff --git a/include/sys/fs/zfs.h b/include/sys/fs/zfs.h
index df5692d14..882e9e84a 100644
--- a/include/sys/fs/zfs.h
+++ b/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
diff --git a/man/man8/zpool.8 b/man/man8/zpool.8
index 63037760a..2cfa8558c 100644
--- a/man/man8/zpool.8
+++ b/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
@@ -1410,6 +1410,17 @@ Used with the \fB-F\fR recovery option. Determines whether a non-importable pool
 .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
+.na
 \fB\fB-m\fR\fR
 .ad
 .sp .6
diff --git a/module/zfs/spa_config.c b/module/zfs/spa_config.c
index 5b95a8e81..c8fe79ed5 100644
--- a/module/zfs/spa_config.c
+++ b/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,