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, 12 insertions, 38 deletions

diff --git a/module/zfs/zfs_ioctl.c b/module/zfs/zfs_ioctl.c
index 746a3f0fc..5c84d238f 100644
--- a/module/zfs/zfs_ioctl.c
+++ b/module/zfs/zfs_ioctl.c
@@ -29,6 +29,7 @@
  * Copyright (c) 2011, 2014 by Delphix. All rights reserved.
  * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
  * Copyright (c) 2013 Steven Hartland. All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 /*
@@ -1499,8 +1500,7 @@ zfs_ioc_pool_destroy(zfs_cmd_t *zc)
 	int error;
 	zfs_log_history(zc);
 	error = spa_destroy(zc->zc_name);
-	if (error == 0)
-		zvol_remove_minors(zc->zc_name);
+
 	return (error);
 }
 
@@ -1552,8 +1552,7 @@ zfs_ioc_pool_export(zfs_cmd_t *zc)
 
 	zfs_log_history(zc);
 	error = spa_export(zc->zc_name, NULL, force, hardforce);
-	if (error == 0)
-		zvol_remove_minors(zc->zc_name);
+
 	return (error);
 }
 
@@ -2394,7 +2393,7 @@ zfs_prop_set_special(const char *dsname, zprop_source_t source,
 		err = zvol_set_volsize(dsname, intval);
 		break;
 	case ZFS_PROP_SNAPDEV:
-		err = zvol_set_snapdev(dsname, intval);
+		err = zvol_set_snapdev(dsname, source, intval);
 		break;
 	case ZFS_PROP_VERSION:
 	{
@@ -3188,12 +3187,6 @@ zfs_ioc_create(const char *fsname, nvlist_t *innvl, nvlist_t *outnvl)
 		if (error != 0)
 			(void) dsl_destroy_head(fsname);
 	}
-
-#ifdef _KERNEL
-	if (error == 0 && type == DMU_OST_ZVOL)
-		zvol_create_minors(fsname);
-#endif
-
 	return (error);
 }
 
@@ -3236,12 +3229,6 @@ zfs_ioc_clone(const char *fsname, nvlist_t *innvl, nvlist_t *outnvl)
 		if (error != 0)
 			(void) dsl_destroy_head(fsname);
 	}
-
-#ifdef _KERNEL
-	if (error == 0)
-		zvol_create_minors(fsname);
-#endif
-
 	return (error);
 }
 
@@ -3304,11 +3291,6 @@ zfs_ioc_snapshot(const char *poolname, nvlist_t *innvl, nvlist_t *outnvl)
 
 	error = dsl_dataset_snapshot(snaps, props, outnvl);
 
-#ifdef _KERNEL
-	if (error == 0)
-		zvol_create_minors(poolname);
-#endif
-
 	return (error);
 }
 
@@ -3434,7 +3416,6 @@ zfs_ioc_destroy_snaps(const char *poolname, nvlist_t *innvl, nvlist_t *outnvl)
 	for (pair = nvlist_next_nvpair(snaps, NULL); pair != NULL;
 	    pair = nvlist_next_nvpair(snaps, pair)) {
 		(void) zfs_unmount_snap(nvpair_name(pair));
-		(void) zvol_remove_minor(nvpair_name(pair));
 	}
 
 	return (dsl_destroy_snapshots_nvl(snaps, defer, outnvl));
@@ -3560,8 +3541,7 @@ zfs_ioc_destroy(zfs_cmd_t *zc)
 		err = dsl_destroy_snapshot(zc->zc_name, zc->zc_defer_destroy);
 	else
 		err = dsl_destroy_head(zc->zc_name);
-	if (zc->zc_objset_type == DMU_OST_ZVOL && err == 0)
-		(void) zvol_remove_minor(zc->zc_name);
+
 	return (err);
 }
 
@@ -4127,11 +4107,6 @@ zfs_ioc_recv(zfs_cmd_t *zc)
 	}
 #endif
 
-#ifdef _KERNEL
-	if (error == 0)
-		zvol_create_minors(tofs);
-#endif
-
 	/*
 	 * On error, restore the original props.
 	 */
@@ -6032,16 +6007,16 @@ _init(void)
 		return (error);
 	}
 
+	if ((error = -zvol_init()) != 0)
+		return (error);
+
 	spa_init(FREAD | FWRITE);
 	zfs_init();
 
-	if ((error = -zvol_init()) != 0)
-		goto out1;
-
 	zfs_ioctl_init();
 
 	if ((error = zfs_attach()) != 0)
-		goto out2;
+		goto out;
 
 	tsd_create(&zfs_fsyncer_key, NULL);
 	tsd_create(&rrw_tsd_key, rrw_tsd_destroy);
@@ -6057,11 +6032,10 @@ _init(void)
 
 	return (0);
 
-out2:
-	(void) zvol_fini();
-out1:
+out:
 	zfs_fini();
 	spa_fini();
+	(void) zvol_fini();
 	printk(KERN_NOTICE "ZFS: Failed to Load ZFS Filesystem v%s-%s%s"
 	    ", rc = %d\n", ZFS_META_VERSION, ZFS_META_RELEASE,
 	    ZFS_DEBUG_STR, error);
@@ -6073,9 +6047,9 @@ static void __exit
 _fini(void)
 {
 	zfs_detach();
-	zvol_fini();
 	zfs_fini();
 	spa_fini();
+	zvol_fini();
 
 	tsd_destroy(&zfs_fsyncer_key);
 	tsd_destroy(&rrw_tsd_key);