[Xen-devel] [PATCH 3/3] xen-blkfront: If no barrier or flush is supported, use invalid operation.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

By default we would set the info->flush_op=0, and zero maps
to BLKIF_OP_READ request code. So if the backend did not support
either barrier ('feature-barrier') or flush ('feature-flush-cache')
we would end up using that opcode for the flush/barrier request, meaning
we actually do a READ request. Fortunatly for us, __generic_make_request
checks q->flush_flags and realizes that we don't do FLUSH and removes
the REQ_FLUSH | REQ_FUA so we never end up issuing a READ request
for a flush request. However, other third party implementations of
__make_request might not be so smart, so lets fix this up.

CC: stable@xxxxxxxxxx
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 drivers/block/xen-blkfront.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index e205d91..c4aa9da 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -97,7 +97,7 @@ struct blkfront_info
        struct blk_shadow shadow[BLK_RING_SIZE];
        unsigned long shadow_free;
        unsigned int feature_flush;
-       unsigned int flush_op;
+       int flush_op;
        unsigned int feature_discard;
        unsigned int discard_granularity;
        unsigned int discard_alignment;
@@ -774,7 +774,7 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
                                if (error == -EOPNOTSUPP)
                                        error = 0;
                                info->feature_flush = 0;
-                               info->flush_op = 0;
+                               info->flush_op = -1; /* 0 is BLKIF_OP_READ */
                                xlvbd_flush(info);
                        }
                        /* fall through */
@@ -1207,7 +1207,7 @@ static void blkfront_connect(struct blkfront_info *info)
        }
 
        info->feature_flush = 0;
-       info->flush_op = 0;
+       info->flush_op = -1; /* 0 is BLKIF_OP_READ */
 
        err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
                            "feature-barrier", "%d", &barrier,
@@ -1234,7 +1234,7 @@ static void blkfront_connect(struct blkfront_info *info)
        if (!err && flush)
                info->flush_op = BLKIF_OP_FLUSH_DISKCACHE;
 
-       if (info->flush_op)
+       if (info->flush_op > 0)
                info->feature_flush = REQ_FLUSH | REQ_FUA;
 
        err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
-- 
1.7.4.1


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