block: deprecate barrier and replace blk_queue_ordered() with blk_queue_flush()

Barrier is deemed too heavy and will soon be replaced by FLUSH/FUA
requests.  Deprecate barrier.  All REQ_HARDBARRIERs are failed with
-EOPNOTSUPP and blk_queue_ordered() is replaced with simpler
blk_queue_flush().

blk_queue_flush() takes combinations of REQ_FLUSH and FUA.  If a
device has write cache and can flush it, it should set REQ_FLUSH.  If
the device can handle FUA writes, it should also set REQ_FUA.

All blk_queue_ordered() users are converted.

* ORDERED_DRAIN is mapped to 0 which is the default value.
* ORDERED_DRAIN_FLUSH is mapped to REQ_FLUSH.
* ORDERED_DRAIN_FLUSH_FUA is mapped to REQ_FLUSH | REQ_FUA.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Boaz Harrosh <bharrosh@panasas.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Alasdair G Kergon <agk@redhat.com>
Cc: Pierre Ossman <drzeus@drzeus.cx>
Cc: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 9 insertions, 16 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 79652809eee8..d10b635b3946 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -388,22 +388,15 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
         vblk->disk->driverfs_dev = &vdev->dev;
         index++;
 
-        if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH)) {
-                /*
-                 * If the FLUSH feature is supported we do have support for
-                 * flushing a volatile write cache on the host.  Use that
-                 * to implement write barrier support.
-                 */
-                blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH);
-        } else {
-                /*
-                 * If the FLUSH feature is not supported we must assume that
-                 * the host does not perform any kind of volatile write
-                 * caching. We still need to drain the queue to provider
-                 * proper barrier semantics.
-                 */
-                blk_queue_ordered(q, QUEUE_ORDERED_DRAIN);
-        }
+        /*
+         * If the FLUSH feature is supported we do have support for
+         * flushing a volatile write cache on the host.  Use that to
+         * implement write barrier support; otherwise, we must assume
+         * that the host does not perform any kind of volatile write
+         * caching.
+         */
+        if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))
+                blk_queue_flush(q, REQ_FLUSH);
 
         /* If disk is read-only in the host, the guest should obey */
         if (virtio_has_feature(vdev, VIRTIO_BLK_F_RO))