[Qemu-devel] [PATCH +stable] block: don't attempt to merge overlapping requests

[Avi Kivity]

The block multiwrite code pretends to be able to merge overlapping requests,
but doesn't do so in fact.  This leads to I/O errors (for example on mkfs
of a large virtio disk).

Signed-off-by: Avi Kivity <address@hidden>
---
 block.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index 48305b7..0e44e26 100644
--- a/block.c
+++ b/block.c
@@ -1956,8 +1956,8 @@ static int multiwrite_merge(BlockDriverState *bs, 
BlockRequest *reqs,
         int64_t oldreq_last = reqs[outidx].sector + reqs[outidx].nb_sectors;
 
         // This handles the cases that are valid for all block drivers, namely
-        // exactly sequential writes and overlapping writes.
-        if (reqs[i].sector <= oldreq_last) {
+        // exactly sequential writes
+        if (reqs[i].sector == oldreq_last) {
             merge = 1;
         }
 
-- 
1.6.6.1