[PATCH] device-mapper: make lock_fs optional

Devices only needs syncing when creating snapshots, so make this optional when
suspending a device.

Signed-off-by: Alasdair G Kergon <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/md/dm-ioctl.c

···
 		return -ENXIO;
 
 	if (!dm_suspended(md))
-		r = dm_suspend(md);
+		r = dm_suspend(md, 1);
 
 	if (!r)
 		r = __dev_status(md, param);
···
 	if (new_map) {
 		/* Suspend if it isn't already suspended */
 		if (!dm_suspended(md))
-			dm_suspend(md);
+			dm_suspend(md, 1);
 
 		r = dm_swap_table(md, new_map);
 		if (r) {

drivers/md/dm.c

···
  */
 #define DMF_BLOCK_IO 0
 #define DMF_SUSPENDED 1
+#define DMF_FROZEN 2
 
 struct mapped_device {
 	struct rw_semaphore io_lock;
···
 		return r;
 	}
 
+	set_bit(DMF_FROZEN, &md->flags);
+
 	/* don't bdput right now, we don't want the bdev
 	 * to go away while it is locked.
 	 */
···
 
 static void unlock_fs(struct mapped_device *md)
 {
+	if (!test_bit(DMF_FROZEN, &md->flags))
+		return;
+
 	thaw_bdev(md->suspended_bdev, md->frozen_sb);
 	md->frozen_sb = NULL;
+	clear_bit(DMF_FROZEN, &md->flags);
 }
 
 /*
···
  * dm_bind_table, dm_suspend must be called to flush any in
  * flight bios and ensure that any further io gets deferred.
  */
-int dm_suspend(struct mapped_device *md)
+int dm_suspend(struct mapped_device *md, int do_lockfs)
 {
 	struct dm_table *map = NULL;
 	DECLARE_WAITQUEUE(wait, current);
···
 	}
 
 	/* Flush I/O to the device. */
-	r = lock_fs(md);
-	if (r)
-		goto out;
+	if (do_lockfs) {
+		r = lock_fs(md);
+		if (r)
+			goto out;
+	}
 
 	/*
 	 * First we set the BLOCK_IO flag so no more ios will be mapped.

drivers/md/dm.h

···
 /*
  * A device can still be used while suspended, but I/O is deferred.
  */
-int dm_suspend(struct mapped_device *md);
+int dm_suspend(struct mapped_device *md, int with_lockfs);
 int dm_resume(struct mapped_device *md);
 
 /*