ext3: make barrier options consistent with ext4

ext4 was updated to accept barrier/nobarrier mount options
in addition to the older barrier=0/1.  The barrier story
is complex enough, we should help people by making the options
the same at least, even if the defaults are different.

This patch allows the barrier/nobarrier mount options for ext3,
while keeping nobarrier the default.

It also unconditionally displays barrier status in show_options,
and prints a message at mount time if barriers are not enabled,
just as ext4 does.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 13 insertions, 2 deletions

diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt
index 867c5b50cb4..272f80d5f96 100644
--- a/Documentation/filesystems/ext3.txt
+++ b/Documentation/filesystems/ext3.txt
@@ -59,8 +59,19 @@ commit=nrsec	(*)	Ext3 can be told to sync all its data and metadata
                         Setting it to very large values will improve
                         performance.
 
-barrier=1               This enables/disables barriers.  barrier=0 disables
-                        it, barrier=1 enables it.
+barrier=<0(*)|1>        This enables/disables the use of write barriers in
+barrier                 the jbd code.  barrier=0 disables, barrier=1 enables.
+nobarrier       (*)     This also requires an IO stack which can support
+                        barriers, and if jbd gets an error on a barrier
+                        write, it will disable again with a warning.
+                        Write barriers enforce proper on-disk ordering
+                        of journal commits, making volatile disk write caches
+                        safe to use, at some performance penalty.  If
+                        your disks are battery-backed in one way or another,
+                        disabling barriers may safely improve performance.
+                        The mount options "barrier" and "nobarrier" can
+                        also be used to enable or disable barriers, for
+                        consistency with other ext3 mount options.
 
 orlov           (*)     This enables the new Orlov block allocator. It is
                         enabled by default.