btrfs: Add nodiscard mount option.

Add nodiscard mount option to disable discard with remount option.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/Documentation/filesystems/btrfs.txt b/Documentation/filesystems/btrfs.txt
index e87609a..7254cf5 100644 (file)
--- a/Documentation/filesystems/btrfs.txt
+++ b/Documentation/filesystems/btrfs.txt
@@ -98,9 +98,12 @@ Options with (*) are default options and will not show in the mount options.
        can be avoided.  Especially useful when trying to mount a multi-device
        setup as root.  May be specified multiple times for multiple devices.
 
+  nodiscard(*)
   discard
-       Issue frequent commands to let the block device reclaim space freed by
-       the filesystem.  This is useful for SSD devices, thinly provisioned
+       Disable/enable discard mount option.
+       Discard issues frequent commands to let the block device reclaim space
+       freed by the filesystem.
+       This is useful for SSD devices, thinly provisioned
        LUNs and virtual machine images, but may have a significant
        performance impact.  (The fstrim command is also available to
        initiate batch trims from userspace).

diff --cc fs/btrfs/super.c
Simple merge