cstyle fixes
dsl_dataset_set_fsid_guid should use ZFS_SPACE_CHECK_RESERVED
dsl_dataset_set_fsid_guid _check and _sync func declared static,
removed from dsl_dataset.h
rewrite unique_valid
6333 ZFS should let the user specify or modify the fsid_guid of a dataset

@@ -1796,10 +1796,12 @@
             ds->ds_quota);
         dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_REFRESERVATION,
             ds->ds_reserved);
         dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_GUID,
             dsl_dataset_phys(ds)->ds_guid);
+        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_FSID_GUID,
+            dsl_dataset_phys(ds)->ds_fsid_guid);
         dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_UNIQUE,
             dsl_dataset_phys(ds)->ds_unique_bytes);
         dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_OBJSETID,
             ds->ds_object);
         dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_USERREFS,

@@ -3503,5 +3505,73 @@
 {
         return (dsl_dataset_is_zapified(ds) &&
             zap_contains(ds->ds_dir->dd_pool->dp_meta_objset,
             ds->ds_object, DS_FIELD_RESUME_TOGUID) == 0);
 }
+
+typedef struct dsl_dataset_set_fsid_guid_arg {
+        const char *ddsfg_name;
+        uint64_t ddsfg_value;
+} dsl_dataset_set_fsid_guid_arg_t;
+
+static int
+dsl_dataset_set_fsid_guid_check(void *arg, dmu_tx_t *tx)
+{
+        int err = 0;
+        dsl_dataset_set_fsid_guid_arg_t *ddsfg = arg;
+        dsl_pool_t *dp = dmu_tx_pool(tx);
+        dsl_dataset_t *ds;
+        uint64_t newval;
+
+        newval = ddsfg->ddsfg_value;
+
+        err = dsl_dataset_hold(dp, ddsfg->ddsfg_name, FTAG, &ds);
+        if (err != 0)
+                return (err);
+
+        /* Check if the FS is mounted */
+        if (ds->ds_owner != NULL) {
+                dsl_dataset_rele(ds, FTAG);
+                return (SET_ERROR(EBUSY));
+        }
+        dsl_dataset_rele(ds, FTAG);
+
+        if (!unique_valid(newval))
+                return (SET_ERROR(EEXIST));
+
+        return (err);
+}
+
+static void
+dsl_dataset_set_fsid_guid_sync(void *arg, dmu_tx_t *tx)
+{
+        dsl_dataset_set_fsid_guid_arg_t *ddsfg = arg;
+        dsl_pool_t *dp = dmu_tx_pool(tx);
+        dsl_dataset_t *ds;
+        uint64_t newval;
+
+        VERIFY0(dsl_dataset_hold(dp, ddsfg->ddsfg_name, FTAG, &ds));
+
+        newval = ddsfg->ddsfg_value;
+
+        dmu_buf_will_dirty(ds->ds_dbuf, tx);
+        mutex_enter(&ds->ds_lock);
+        ds->ds_fsid_guid = newval;
+        dsl_dataset_phys(ds)->ds_fsid_guid = newval;
+        mutex_exit(&ds->ds_lock);
+
+        dsl_dataset_rele(ds, FTAG);
+}
+
+int
+dsl_dataset_set_fsid_guid(const char *ddname, zprop_source_t source,
+    uint64_t fsid_guid)
+{
+        dsl_dataset_set_fsid_guid_arg_t ddsfg;
+
+        ddsfg.ddsfg_name = ddname;
+        ddsfg.ddsfg_value = fsid_guid;
+
+        return (dsl_sync_task(ddname, dsl_dataset_set_fsid_guid_check,
+            dsl_dataset_set_fsid_guid_sync, &ddsfg, 0,
+            ZFS_SPACE_CHECK_RESERVED));
+}