btrfs-progs doc: emphasis that only mounted device works for btrfs device stats

We provided format <path>|<device> in command line.
But btrfs device stats doesn't work if device is not mounted.

Also fix some tailing whitespace.

Signed-off-by: Chen Hanxiao <chenhanxiao@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>

diff --git a/Documentation/btrfs-device.txt b/Documentation/btrfs-device.txt
index 66be6b3..075ccc5 100644 (file)
--- a/Documentation/btrfs-device.txt
+++ b/Documentation/btrfs-device.txt
@@ -83,14 +83,14 @@ Check device to see if it has all of it's devices in cache for mounting.
 *scan* [(--all-devices|-d)|<device> [<device>...]]::
 Scan devices for a btrfs filesystem.
 +
 *scan* [(--all-devices|-d)|<device> [<device>...]]::
 Scan devices for a btrfs filesystem.
 +

-If one or more devices are passed, these are scanned for a btrfs filesystem. 
+If one or more devices are passed, these are scanned for a btrfs filesystem.

 If no devices are passed, btrfs uses block devices containing btrfs
 filesystem as listed by blkid.
 If no devices are passed, btrfs uses block devices containing btrfs
 filesystem as listed by blkid.

-Finally, if '--all-devices' or '-d' is passed, all the devices under /dev are 
+Finally, if '--all-devices' or '-d' is passed, all the devices under /dev are

 scanned.
 
 *stats* [-z] <path>|<device>::
 scanned.
 
 *stats* [-z] <path>|<device>::

-Read and print the device IO stats for all devices of the filesystem
+Read and print the device IO stats for all mounted devices of the filesystem

 identified by <path> or for a single <device>.
 +
 `Options`
 identified by <path> or for a single <device>.
 +
 `Options`