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

2 files changed, 9 insertions, 8 deletions

diff --git a/include/sys/spa_impl.h b/include/sys/spa_impl.h
index 0bb6dccdc..759c3472f 100644
--- a/include/sys/spa_impl.h
+++ b/include/sys/spa_impl.h
@@ -23,6 +23,7 @@
  * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 #ifndef _SYS_SPA_IMPL_H
@@ -253,6 +254,7 @@ struct spa {
 	uint64_t	spa_errata;		/* errata issues detected */
 	spa_stats_t	spa_stats;		/* assorted spa statistics */
 	hrtime_t	spa_ccw_fail_time;	/* Conf cache write fail time */
+	taskq_t		*spa_zvol_taskq;	/* Taskq for minor managment */
 
 	/*
 	 * spa_refcount & spa_config_lock must be the last elements
diff --git a/include/sys/zvol.h b/include/sys/zvol.h
index 898e23521..c3e386f0b 100644
--- a/include/sys/zvol.h
+++ b/include/sys/zvol.h
@@ -21,6 +21,7 @@
 
 /*
  * Copyright (c) 2006, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2016 Actifio, Inc. All rights reserved.
  */
 
 #ifndef	_SYS_ZVOL_H
@@ -31,24 +32,22 @@
 #define	ZVOL_OBJ		1ULL
 #define	ZVOL_ZAP_OBJ		2ULL
 
-#ifdef _KERNEL
+extern void zvol_create_minors(spa_t *spa, const char *name, boolean_t async);
+extern void zvol_remove_minors(spa_t *spa, const char *name, boolean_t async);
+extern void zvol_rename_minors(spa_t *spa, const char *oldname,
+    const char *newname, boolean_t async);
 
+#ifdef _KERNEL
 extern int zvol_check_volsize(uint64_t volsize, uint64_t blocksize);
 extern int zvol_check_volblocksize(const char *name, uint64_t volblocksize);
 extern int zvol_get_stats(objset_t *os, nvlist_t *nv);
 extern boolean_t zvol_is_zvol(const char *);
 extern void zvol_create_cb(objset_t *os, void *arg, cred_t *cr, dmu_tx_t *tx);
-extern int zvol_create_minor(const char *name);
-extern int zvol_create_minors(const char *name);
-extern int zvol_remove_minor(const char *name);
-extern void zvol_remove_minors(const char *name);
-extern void zvol_rename_minors(const char *oldname, const char *newname);
 extern int zvol_set_volsize(const char *, uint64_t);
 extern int zvol_set_volblocksize(const char *, uint64_t);
-extern int zvol_set_snapdev(const char *, uint64_t);
+extern int zvol_set_snapdev(const char *, zprop_source_t, uint64_t);
 
 extern int zvol_init(void);
 extern void zvol_fini(void);
-
 #endif /* _KERNEL */
 #endif /* _SYS_ZVOL_H */