[Xen-devel] [PATCH 4/4] xen/blkfront: cope with backend that fail empty BLKIF_OP_WRITE_BARRIER requests

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

Some(?) Xen block backends fail BLKIF_OP_WRITE_BARRIER requests, which
Linux uses as a cache flush operation.  In that case, disable use
of FLUSH.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Cc: Daniel Stodden <daniel.stodden@xxxxxxxxxx>
---
 drivers/block/xen-blkfront.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 76b874a..5e5a622 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -656,6 +656,14 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
                                printk(KERN_WARNING "blkfront: %s: write 
barrier op failed\n",
                                       info->gd->disk_name);
                                error = -EOPNOTSUPP;
+                       }
+                       if (unlikely(bret->status == BLKIF_RSP_ERROR &&
+                                    info->shadow[id].req.nr_segments == 0)) {
+                               printk(KERN_WARNING "blkfront: %s: empty write 
barrier op failed\n",
+                                      info->gd->disk_name);
+                               error = -EOPNOTSUPP;
+                       }
+                       if (unlikely(error)) {
                                info->feature_flush = 0;
                                xlvbd_flush(info);
                        }
-- 
1.7.2.3


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