From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Date: Tue, 2 Nov 2010 15:55:58 +0000 (-0400)
Subject: xen/blkfront: cope with backend that fail empty BLKIF_OP_WRITE_BARRIER requests
X-Git-Tag: 2.1b_release~6170^2~4^2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=dcb8baeceaa1c629bbd06f472cea023ad08a0c33;p=platform%2Fkernel%2Fkernel-mfld-blackbay.git

xen/blkfront: cope with backend that fail empty BLKIF_OP_WRITE_BARRIER requests

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@citrix.com>
Cc: Daniel Stodden <daniel.stodden@citrix.com>
---

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 76b874a..4f9e22f 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -656,6 +656,16 @@ 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)) {
+				if (error == -EOPNOTSUPP)
+					error = 0;
 				info->feature_flush = 0;
 				xlvbd_flush(info);
 			}