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>

diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt
index 867c5b5..272f80d 100644 (file)
--- 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.

diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index 6b6e49d..0fc1293 100644 (file)
--- a/fs/ext3/super.c
+++ b/fs/ext3/super.c
@@ -653,8 +653,12 @@ static int ext3_show_options(struct seq_file *seq, struct vfsmount *vfs)
                seq_printf(seq, ",commit=%u",
                           (unsigned) (sbi->s_commit_interval / HZ));
        }
-       if (test_opt(sb, BARRIER))
-               seq_puts(seq, ",barrier=1");
+
+       /*
+        * Always display barrier state so it's clear what the status is.
+        */
+       seq_puts(seq, ",barrier=");
+       seq_puts(seq, test_opt(sb, BARRIER) ? "1" : "0");
        if (test_opt(sb, NOBH))
                seq_puts(seq, ",nobh");
 
@@ -810,8 +814,8 @@ enum {
        Opt_data_err_abort, Opt_data_err_ignore,
        Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
        Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_jqfmt_vfsv1, Opt_quota,
-       Opt_noquota, Opt_ignore, Opt_barrier, Opt_err, Opt_resize,
-       Opt_usrquota, Opt_grpquota
+       Opt_noquota, Opt_ignore, Opt_barrier, Opt_nobarrier, Opt_err,
+       Opt_resize, Opt_usrquota, Opt_grpquota
 };
 
 static const match_table_t tokens = {
@@ -865,6 +869,8 @@ static const match_table_t tokens = {
        {Opt_quota, "quota"},
        {Opt_usrquota, "usrquota"},
        {Opt_barrier, "barrier=%u"},
+       {Opt_barrier, "barrier"},
+       {Opt_nobarrier, "nobarrier"},
        {Opt_resize, "resize"},
        {Opt_err, NULL},
 };
@@ -967,7 +973,11 @@ static int parse_options (char *options, struct super_block *sb,
                int token;
                if (!*p)
                        continue;
-
+               /*
+                * Initialize args struct so we know whether arg was
+                * found; some options take optional arguments.
+                */
+               args[0].to = args[0].from = 0;
                token = match_token(p, tokens, args);
                switch (token) {
                case Opt_bsd_df:
@@ -1215,9 +1225,15 @@ set_qf_format:
                case Opt_abort:
                        set_opt(sbi->s_mount_opt, ABORT);
                        break;
+               case Opt_nobarrier:
+                       clear_opt(sbi->s_mount_opt, BARRIER);
+                       break;
                case Opt_barrier:
-                       if (match_int(&args[0], &option))
-                               return 0;
+                       if (args[0].from) {
+                               if (match_int(&args[0], &option))
+                                       return 0;
+                       } else
+                               option = 1;     /* No argument, default to 1 */
                        if (option)
                                set_opt(sbi->s_mount_opt, BARRIER);
                        else
@@ -2276,6 +2292,9 @@ static int ext3_load_journal(struct super_block *sb,
                        return -EINVAL;
        }
 
+       if (!(journal->j_flags & JFS_BARRIER))
+               printk(KERN_INFO "EXT3-fs: barriers not enabled\n");
+
        if (!really_read_only && test_opt(sb, UPDATE_JOURNAL)) {
                err = journal_update_format(journal);
                if (err)  {