[Xen-devel] [PATCH 3/4] xen/blkfront: Implement FUA with BLKIF_OP_WRITE_BARRIER

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

The BLKIF_OP_WRITE_BARRIER is a full ordered barrier, so we can use it
to implement FUA as well as a plain FLUSH.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Acked-by: Christoph Hellwig <hch@xxxxxx>
---
 drivers/block/xen-blkfront.c |   14 ++++++++++++--
 1 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 31c8a64..76b874a 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -286,8 +286,18 @@ static int blkif_queue_request(struct request *req)
 
        ring_req->operation = rq_data_dir(req) ?
                BLKIF_OP_WRITE : BLKIF_OP_READ;
-       if (req->cmd_flags & REQ_FLUSH)
+
+       if (req->cmd_flags & (REQ_FLUSH | REQ_FUA)) {
+               /*
+                * Ideally we could just do an unordered
+                * flush-to-disk, but all we have is a full write
+                * barrier at the moment.  However, a barrier write is
+                * a superset of FUA, so we can implement it the same
+                * way.  (It's also a FLUSH+FUA, since it is
+                * guaranteed ordered WRT previous writes.)
+                */
                ring_req->operation = BLKIF_OP_WRITE_BARRIER;
+       }
 
        ring_req->nr_segments = blk_rq_map_sg(req->q, req, info->sg);
        BUG_ON(ring_req->nr_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
@@ -1065,7 +1075,7 @@ static void blkfront_connect(struct blkfront_info *info)
        info->feature_flush = 0;
 
        if (!err && barrier)
-               info->feature_flush = REQ_FLUSH;
+               info->feature_flush = REQ_FLUSH | REQ_FUA;
 
        err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
        if (err) {
-- 
1.7.2.3


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