btrfs: Add noenospc_debug mount option.

Add noenospc_debug mount option to disable ENOSPC debug with
remount option.

Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

Documentation/filesystems/btrfs.txt

@@ -108,8 +108,9 @@ Options with (*) are default options and will not show in the mount options.
 	performance impact.  (The fstrim command is also available to
 	initiate batch trims from userspace).
 
+  noenospc_debug(*)
   enospc_debug
-	Debugging option to be more verbose in some ENOSPC conditions.
+	Disable/enable debugging option to be more verbose in some ENOSPC conditions.
 
   fatal_errors=<action>
 	Action to take when encountering a fatal error: 

fs/btrfs/super.c

@@ -324,6 +324,7 @@ enum {
 	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_barrier, Opt_nodefrag, Opt_nodiscard,
+	Opt_noenospc_debug,
 	Opt_err,
 };
 
@@ -356,6 +357,7 @@ static match_table_t tokens = {
 	{Opt_clear_cache, "clear_cache"},
 	{Opt_user_subvol_rm_allowed, "user_subvol_rm_allowed"},
 	{Opt_enospc_debug, "enospc_debug"},
+	{Opt_noenospc_debug, "noenospc_debug"},
 	{Opt_subvolrootid, "subvolrootid=%d"},
 	{Opt_defrag, "autodefrag"},
 	{Opt_nodefrag, "noautodefrag"},
@@ -603,6 +605,9 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 		case Opt_enospc_debug:
 			btrfs_set_opt(info->mount_opt, ENOSPC_DEBUG);
 			break;
+		case Opt_noenospc_debug:
+			btrfs_clear_opt(info->mount_opt, ENOSPC_DEBUG);
+			break;
 		case Opt_defrag:
 			btrfs_info(root->fs_info, "enabling auto defrag");
 			btrfs_set_opt(info->mount_opt, AUTO_DEFRAG);