Hi Jens,
Today's linux-next merge of the block tree got a conflict in
drivers/block/virtio_blk.c between commit
0e41b2d3ea0f5bf472a2b163c54305f62ab7b776 ("virtio_blk: support barriers
without FLUSH feature") from the rr tree and commits
3789fdefa13bcaa7ad06d952ac6010f0a81bf04e ("virtio_blk: stop using
q->prepare_flush_fn") and 5e27e27e73b5bff903b3c30ffd5a0e17eb95c087
("block: remove q->prepare_flush_fn completely") from the block tree.
I fixed it up (see below) and can carry the fix as necessary.
--
Cheers,
Stephen Rothwell sfr@xxxxxxxxxxxxxxxx
diff --cc drivers/block/virtio_blk.c
index 23b7c48,0a3222f..0000000
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@@ -377,32 -364,11 +375,31 @@@ static int __devinit virtblk_probe(stru
vblk->disk->driverfs_dev = &vdev->dev;
index++;
- /* If barriers are supported, tell block layer that queue is ordered */
- if (virtio_has_feature(vdev, VIRTIO_BLK_F_FLUSH))
+ 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,
- virtblk_prepare_flush);
+ blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH);
- else if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER))
+ } else if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER)) {
+ /*
+ * If the BARRIER feature is supported the host expects us
+ * to order request by tags. This implies there is not
+ * volatile write cache on the host, and that the host
+ * never re-orders outstanding I/O. This feature is not
+ * useful for real life scenarious and deprecated.
+ */
- blk_queue_ordered(q, QUEUE_ORDERED_TAG, NULL);
+ blk_queue_ordered(q, QUEUE_ORDERED_TAG);
+ } 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, NULL);
++ blk_queue_ordered(q, QUEUE_ORDERED_DRAIN);
+ }
/* If disk is read-only in the host, the guest should obey */
if (virtio_has_feature(vdev, VIRTIO_BLK_F_RO))
--
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