From 254db57f9b12daba841a4d91ddb9a8161e9c74ba Mon Sep 17 00:00:00 2001
From: Steven Whitehouse <swhiteho@redhat.com>
Date: Fri, 26 Sep 2008 10:23:22 +0100
Subject: [PATCH] GFS2: Support for I/O barriers

This patch adds barrier support to GFS2. There is not a lot of change
really... we just add the barrier flag when we write journal header
blocks. If the underlying device refuses to support them, we fall back
to the previous way of doing things (wait for the I/O and hope) since
there is nothing else we can do. There is no user configuration,
barriers will always be on unless the device refuses to support them.
This seems a reasonable solution to me since this is a correctness
issue.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
---
 fs/gfs2/incore.h |  1 +
 fs/gfs2/log.c    | 21 ++++++++++++++++++---
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index f1ed3a1bf8aa..f566ec1b4e8e 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -432,6 +432,7 @@ enum {
 	SDF_JOURNAL_CHECKED	= 0,
 	SDF_JOURNAL_LIVE	= 1,
 	SDF_SHUTDOWN		= 2,
+	SDF_NOBARRIERS		= 3,
 };
 
 #define GFS2_FSNAME_LEN		256
diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 6c6af9f5e3ab..ad305854bdc6 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -18,6 +18,7 @@
 #include <linux/delay.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
+#include <linux/bio.h>
 
 #include "gfs2.h"
 #include "incore.h"
@@ -584,7 +585,6 @@ static void log_write_header(struct gfs2_sbd *sdp, u32 flags, int pull)
 	memset(bh->b_data, 0, bh->b_size);
 	set_buffer_uptodate(bh);
 	clear_buffer_dirty(bh);
-	unlock_buffer(bh);
 
 	gfs2_ail1_empty(sdp, 0);
 	tail = current_tail(sdp);
@@ -601,8 +601,23 @@ static void log_write_header(struct gfs2_sbd *sdp, u32 flags, int pull)
 	hash = gfs2_disk_hash(bh->b_data, sizeof(struct gfs2_log_header));
 	lh->lh_hash = cpu_to_be32(hash);
 
-	set_buffer_dirty(bh);
-	if (sync_dirty_buffer(bh))
+	bh->b_end_io = end_buffer_write_sync;
+	if (test_bit(SDF_NOBARRIERS, &sdp->sd_flags))
+		goto skip_barrier;
+	get_bh(bh);
+	submit_bh(WRITE_BARRIER | (1 << BIO_RW_META), bh);
+	wait_on_buffer(bh);
+	if (buffer_eopnotsupp(bh)) {
+		clear_buffer_eopnotsupp(bh);
+		set_buffer_uptodate(bh);
+		set_bit(SDF_NOBARRIERS, &sdp->sd_flags);
+		lock_buffer(bh);
+skip_barrier:
+		get_bh(bh);
+		submit_bh(WRITE_SYNC | (1 << BIO_RW_META), bh);
+		wait_on_buffer(bh);
+	}
+	if (!buffer_uptodate(bh))
 		gfs2_io_error_bh(sdp, bh);
 	brelse(bh);