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[Xen-changelog] [linux-2.6.18-xen] xen/blkback: don't fail empty barrier

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Subject: [Xen-changelog] [linux-2.6.18-xen] xen/blkback: don't fail empty barrier requests
From: Xen patchbot-linux-2.6.18-xen <patchbot@xxxxxxx>
Date: Thu, 26 May 2011 12:50:05 +0100
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# HG changeset patch
# User Jan Beulich <jbeulich@xxxxxxxxxx>
# Date 1306409621 -3600
# Node ID 876a5aaac0264cf38cae6581e5714b93ec380aaa
# Parent  aedb712c05cf065e943e15d0f38597c2e80f7982
xen/blkback: don't fail empty barrier requests

The sector number on empty barrier requests may (will?) be
uninitialized (neither bio_init() nor rq_init() set the respective
fields), which allows for exceeding the actual (virtual) disk's size.

Inspired by Konrad's "When writting barriers set the sector number to
zero...", but instead of zapping the sector number (which is wrong for
non-empty ones) just ignore the sector number when the sector count is

While at it also add overflow checking to the math in vbd_translate().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

diff -r aedb712c05cf -r 876a5aaac026 drivers/xen/blkback/vbd.c
--- a/drivers/xen/blkback/vbd.c Thu May 26 08:09:04 2011 +0100
+++ b/drivers/xen/blkback/vbd.c Thu May 26 12:33:41 2011 +0100
@@ -108,8 +108,14 @@
        if ((operation != READ) && vbd->readonly)
                goto out;
-       if (unlikely((req->sector_number + req->nr_sects) > vbd_sz(vbd)))
-               goto out;
+       if (likely(req->nr_sects)) {
+               blkif_sector_t end = req->sector_number + req->nr_sects;
+               if (unlikely(end < req->sector_number))
+                       goto out;
+               if (unlikely(end > vbd_sz(vbd)))
+                       goto out;
+       }
        req->dev  = vbd->pdevice;
        req->bdev = vbd->bdev;

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