GFS2: add barrier/nobarrier mount options

Currently gfs2 issues barrier unconditionally.  There are various reasons
to disable them, be that just for testing or for stupid devices flushing
large battert backed caches.  Add a nobarrier option that matches xfs and
btrfs for this.  Also add a symmetric barrier option to turn it back on
at remount time.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/incore.h

@@ -429,6 +429,7 @@ struct gfs2_args {
 	unsigned int ar_meta:1;			/* mount metafs */
 	unsigned int ar_discard:1;		/* discard requests */
 	unsigned int ar_errors:2;               /* errors=withdraw | panic */
+	unsigned int ar_nobarrier:1;            /* do not send barriers */
 	int ar_commit;				/* Commit interval */
 	int ar_statfs_quantum;			/* The fast statfs interval */
 	int ar_quota_quantum;			/* The quota interval */

fs/gfs2/ops_fstype.c

@@ -1131,6 +1131,8 @@ static int fill_super(struct super_block *sb, struct gfs2_args *args, int silent
 	}
 	if (sdp->sd_args.ar_posix_acl)
 		sb->s_flags |= MS_POSIXACL;
+	if (sdp->sd_args.ar_nobarrier)
+		set_bit(SDF_NOBARRIERS, &sdp->sd_flags);
 
 	sb->s_magic = GFS2_MAGIC;
 	sb->s_op = &gfs2_super_ops;

fs/gfs2/super.c

@@ -73,6 +73,8 @@ enum {
 	Opt_statfs_quantum,
 	Opt_statfs_percent,
 	Opt_quota_quantum,
+	Opt_barrier,
+	Opt_nobarrier,
 	Opt_error,
 };
 
@@ -107,6 +109,8 @@ static const match_table_t tokens = {
 	{Opt_statfs_quantum, "statfs_quantum=%d"},
 	{Opt_statfs_percent, "statfs_percent=%d"},
 	{Opt_quota_quantum, "quota_quantum=%d"},
+	{Opt_barrier, "barrier"},
+	{Opt_nobarrier, "nobarrier"},
 	{Opt_error, NULL}
 };
 
@@ -253,6 +257,12 @@ int gfs2_mount_args(struct gfs2_args *args, char *options)
 			}
 			args->ar_errors = GFS2_ERRORS_PANIC;
 			break;
+		case Opt_barrier:
+			args->ar_nobarrier = 0;
+			break;
+		case Opt_nobarrier:
+			args->ar_nobarrier = 1;
+			break;
 		case Opt_error:
 		default:
 			printk(KERN_WARNING "GFS2: invalid mount option: %s\n", o);
@@ -1143,6 +1153,10 @@ static int gfs2_remount_fs(struct super_block *sb, int *flags, char *data)
 		sb->s_flags |= MS_POSIXACL;
 	else
 		sb->s_flags &= ~MS_POSIXACL;
+	if (sdp->sd_args.ar_nobarrier)
+		set_bit(SDF_NOBARRIERS, &sdp->sd_flags);
+	else
+		clear_bit(SDF_NOBARRIERS, &sdp->sd_flags);
 	spin_lock(&gt->gt_spin);
 	gt->gt_log_flush_secs = args.ar_commit;
 	gt->gt_quota_quantum = args.ar_quota_quantum;