5882 Temporary pool names
Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: Igor Kozhukhov <igor@dilos.org>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Approved by: Dan McDonald <danmcd@joyent.com>

@@ -206,10 +206,11 @@
 {
         spa_config_dirent_t *dp, *tdp;
         nvlist_t *nvl;
         boolean_t ccw_failure;
         int error;
+        char *pool_name;
 
         ASSERT(MUTEX_HELD(&spa_namespace_lock));
 
         if (rootdir == NULL || !(spa_mode_global & FWRITE))
                 return;

@@ -252,11 +253,18 @@
                         }
 
                         if (nvl == NULL)
                                 nvl = fnvlist_alloc();
 
-                        fnvlist_add_nvlist(nvl, spa->spa_name,
+                        if (spa->spa_import_flags & ZFS_IMPORT_TEMP_NAME) {
+                                pool_name = fnvlist_lookup_string(
+                                    spa->spa_config, ZPOOL_CONFIG_POOL_NAME);
+                        } else {
+                                pool_name = spa_name(spa);
+                        }
+
+                        fnvlist_add_nvlist(nvl, pool_name,
                             spa->spa_config);
                         mutex_exit(&spa->spa_props_lock);
                 }
 
                 error = spa_config_write(dp, nvl);

@@ -357,10 +365,11 @@
         nvlist_t *config, *nvroot;
         vdev_t *rvd = spa->spa_root_vdev;
         unsigned long hostid = 0;
         boolean_t locked = B_FALSE;
         uint64_t split_guid;
+        char *pool_name;
 
         if (vd == NULL) {
                 vd = rvd;
                 locked = B_TRUE;
                 spa_config_enter(spa, SCL_CONFIG | SCL_STATE, FTAG, RW_READER);

@@ -373,14 +382,31 @@
          * If txg is -1, report the current value of spa->spa_config_txg.
          */
         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) {
+                pool_name = fnvlist_lookup_string(spa->spa_config,
+                    ZPOOL_CONFIG_POOL_NAME);
+        } else {
+                pool_name = spa_name(spa);
+        }
+
         config = fnvlist_alloc();
 
         fnvlist_add_uint64(config, ZPOOL_CONFIG_VERSION, spa_version(spa));
-        fnvlist_add_string(config, ZPOOL_CONFIG_POOL_NAME, spa_name(spa));
+        fnvlist_add_string(config, ZPOOL_CONFIG_POOL_NAME, pool_name);
         fnvlist_add_uint64(config, ZPOOL_CONFIG_POOL_STATE, spa_state(spa));
         fnvlist_add_uint64(config, ZPOOL_CONFIG_POOL_TXG, txg);
         fnvlist_add_uint64(config, ZPOOL_CONFIG_POOL_GUID, spa_guid(spa));
         if (spa->spa_comment != NULL) {
                 fnvlist_add_string(config, ZPOOL_CONFIG_COMMENT,