Perform hardware cache flush on all disks during barrier operation.

This makes it possible to enable hardware write cache for linear mappings.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 drivers/md/dm-table.c |   16 ++++++++++++++++
 drivers/md/dm.c       |    9 ++++++++-
 drivers/md/dm.h       |    1 +
 3 files changed, 25 insertions(+), 1 deletion(-)

Index: linux-2.6.28-clean/drivers/md/dm-table.c
===================================================================
--- linux-2.6.28-clean.orig/drivers/md/dm-table.c	2009-01-12 15:16:29.000000000 +0100
+++ linux-2.6.28-clean/drivers/md/dm-table.c	2009-01-12 15:19:46.000000000 +0100
@@ -979,6 +979,22 @@ void dm_table_unplug_all(struct dm_table
 	}
 }
 
+int dm_table_flush_all(struct dm_table *t)
+{
+	int error = 0;
+	struct dm_dev_internal *dd;
+	struct list_head *devices = dm_table_get_devices(t);
+
+	list_for_each_entry(dd, devices, list) {
+		/* !!! TODO: concurrent flush */
+		int r = blkdev_issue_flush(dd->dm_dev.bdev, NULL);
+		if (unlikely(r) && unlikely(r != -EOPNOTSUPP) && !error)
+			error = r;
+	}
+
+	return error;
+}
+
 struct mapped_device *dm_table_get_md(struct dm_table *t)
 {
 	dm_get(t->md);
Index: linux-2.6.28-clean/drivers/md/dm.c
===================================================================
--- linux-2.6.28-clean.orig/drivers/md/dm.c	2009-01-12 15:19:40.000000000 +0100
+++ linux-2.6.28-clean/drivers/md/dm.c	2009-01-12 15:19:46.000000000 +0100
@@ -1363,8 +1363,15 @@ static int dm_wait_for_completion(struct
 
 static int dm_flush(struct mapped_device *md)
 {
+	int error;
+	struct dm_table *map;
 	dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);
-	return 0;
+	map = dm_get_table(md);
+	if (!map)
+		return 0;
+	error = dm_table_flush_all(map);
+	dm_table_put(map);
+	return error;
 }
 
 static void __merge_pushback_list(struct mapped_device *md)
Index: linux-2.6.28-clean/drivers/md/dm.h
===================================================================
--- linux-2.6.28-clean.orig/drivers/md/dm.h	2009-01-12 15:16:29.000000000 +0100
+++ linux-2.6.28-clean/drivers/md/dm.h	2009-01-12 15:19:46.000000000 +0100
@@ -46,6 +46,7 @@ void dm_table_presuspend_targets(struct 
 void dm_table_postsuspend_targets(struct dm_table *t);
 int dm_table_resume_targets(struct dm_table *t);
 int dm_table_any_congested(struct dm_table *t, int bdi_bits);
+int dm_table_flush_all(struct dm_table *t);
 
 /*
  * To check the return value from dm_table_find_target().