2 files changed, 39 insertions, 9 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.
diff --git a/fs/ext3/super.c b/fs/ext3/super.c
index 6b6e49de091..0fc1293d0e9 100644
--- 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)  {