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

*** 1796,1805 ****
--- 1796,1807 ----
              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,
*** 3503,3507 ****
--- 3505,3577 ----
  {
          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));
+ }