Add support for asynchronous zvol minor operations

zfsonlinux issue #2217 - zvol minor operations: check snapdev
property before traversing snapshots of a dataset

zfsonlinux issue #3681 - lock order inversion between zvol_open()
and dsl_pool_sync()...zvol_rename_minors()

Create a per-pool zvol taskq for asynchronous zvol tasks.
There are a few key design decisions to be aware of.

* Each taskq must be single threaded to ensure tasks are always
  processed in the order in which they were dispatched.

* There is a taskq per-pool in order to keep the pools independent.
  This way if one pool is suspended it will not impact another.

* The preferred location to dispatch a zvol minor task is a sync
  task.  In this context there is easy access to the spa_t and
  minimal error handling is required because the sync task must
  succeed.

Support for asynchronous zvol minor operations address issue #3681.

Signed-off-by: Boris Protopopov <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #2217
Closes #3678
Closes #3681

1 files changed, 6 insertions, 30 deletions

diff --git a/module/zfs/dsl_dataset.c b/module/zfs/dsl_dataset.c
index a5a9694fc..230027daf 100644
--- a/module/zfs/dsl_dataset.c
+++ b/module/zfs/dsl_dataset.c
@@ -24,6 +24,7 @@
  * Copyright (c) 2014, Joyent, Inc. All rights reserved.
  * Copyright (c) 2014 RackTop Systems.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 #include <sys/dmu_objset.h>
@@ -1424,6 +1425,7 @@ dsl_dataset_snapshot_sync(void *arg, dmu_tx_t *tx)
 			dsl_props_set_sync_impl(ds->ds_prev,
 			    ZPROP_SRC_LOCAL, ddsa->ddsa_props, tx);
 		}
+		zvol_create_minors(dp->dp_spa, nvpair_name(pair), B_TRUE);
 		dsl_dataset_rele(ds, FTAG);
 	}
 }
@@ -1498,16 +1500,6 @@ dsl_dataset_snapshot(nvlist_t *snaps, nvlist_t *props, nvlist_t *errors)
 		fnvlist_free(suspended);
 	}
 
-#ifdef _KERNEL
-	if (error == 0) {
-		for (pair = nvlist_next_nvpair(snaps, NULL); pair != NULL;
-		    pair = nvlist_next_nvpair(snaps, pair)) {
-			char *snapname = nvpair_name(pair);
-			zvol_create_minors(snapname);
-		}
-	}
-#endif
-
 	return (error);
 }
 
@@ -1930,6 +1922,8 @@ dsl_dataset_rename_snapshot_sync_impl(dsl_pool_t *dp,
 	VERIFY0(zap_add(dp->dp_meta_objset,
 	    dsl_dataset_phys(hds)->ds_snapnames_zapobj,
 	    ds->ds_snapname, 8, 1, &ds->ds_object, tx));
+	zvol_rename_minors(dp->dp_spa, ddrsa->ddrsa_oldsnapname,
+	    ddrsa->ddrsa_newsnapname, B_TRUE);
 
 	dsl_dataset_rele(ds, FTAG);
 	return (0);
@@ -1958,11 +1952,6 @@ int
 dsl_dataset_rename_snapshot(const char *fsname,
     const char *oldsnapname, const char *newsnapname, boolean_t recursive)
 {
-#ifdef _KERNEL
-	char *oldname, *newname;
-#endif
-	int error;
-
 	dsl_dataset_rename_snapshot_arg_t ddrsa;
 
 	ddrsa.ddrsa_fsname = fsname;
@@ -1970,22 +1959,9 @@ dsl_dataset_rename_snapshot(const char *fsname,
 	ddrsa.ddrsa_newsnapname = newsnapname;
 	ddrsa.ddrsa_recursive = recursive;
 
-	error = dsl_sync_task(fsname, dsl_dataset_rename_snapshot_check,
+	return (dsl_sync_task(fsname, dsl_dataset_rename_snapshot_check,
 	    dsl_dataset_rename_snapshot_sync, &ddrsa,
-	    1, ZFS_SPACE_CHECK_RESERVED);
-
-	if (error)
-	    return (SET_ERROR(error));
-
-#ifdef _KERNEL
-	oldname = kmem_asprintf("%s@%s", fsname, oldsnapname);
-	newname = kmem_asprintf("%s@%s", fsname, newsnapname);
-	zvol_rename_minors(oldname, newname);
-	strfree(newname);
-	strfree(oldname);
-#endif
-
-	return (0);
+	    1, ZFS_SPACE_CHECK_RESERVED));
 }
 
 /*