btrfs: Add "barrier" option to support "-o remount,barrier"

Btrfs can be remounted without barrier, but there is no "barrier" option
so nobody can remount btrfs back with barrier on. Only umount and
mount again can re-enable barrier.(Quite awkward)

Also the mount options in the document is also changed slightly for the
further pairing options changes.

Reported-by: Daniel Blueman <daniel@quora.org>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Mike Fleetwood <mike.fleetwood@googlemail.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 15b6a1d4c533..b02d25a64b2e 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -323,7 +323,7 @@ enum {
         Opt_no_space_cache, Opt_recovery, Opt_skip_balance,
         Opt_check_integrity, Opt_check_integrity_including_extent_data,
         Opt_check_integrity_print_mask, Opt_fatal_errors, Opt_rescan_uuid_tree,
-        Opt_commit_interval,
+        Opt_commit_interval, Opt_barrier,
         Opt_err,
 };
 
@@ -335,6 +335,7 @@ static match_table_t tokens = {
         {Opt_nodatasum, "nodatasum"},
         {Opt_nodatacow, "nodatacow"},
         {Opt_nobarrier, "nobarrier"},
+        {Opt_barrier, "barrier"},
         {Opt_max_inline, "max_inline=%s"},
         {Opt_alloc_start, "alloc_start=%s"},
         {Opt_thread_pool, "thread_pool=%d"},
@@ -494,6 +495,11 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
                         btrfs_clear_opt(info->mount_opt, SSD);
                         btrfs_clear_opt(info->mount_opt, SSD_SPREAD);
                         break;
+                case Opt_barrier:
+                        if (btrfs_test_opt(root, NOBARRIER))
+                                btrfs_info(root->fs_info, "turning on barriers");
+                        btrfs_clear_opt(info->mount_opt, NOBARRIER);
+                        break;
                 case Opt_nobarrier:
                         btrfs_info(root->fs_info, "turning off barriers");
                         btrfs_set_opt(info->mount_opt, NOBARRIER);