From 391827eb106d2d02062b2582d1545a7c221631c6 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Wed, 30 Jul 2014 09:53:30 +0100 Subject: [PATCH] block: fix overlapping multiwrite requests When request A is a strict superset of request B: AAAAAAAA BBBB multiwrite_merge() merges them as follows: AABBBB The tail of request A should have been included: AABBBBAA This patch fixes data loss but this code path is probably rare. Since guests cannot assume ordering between in-flight requests, few applications submit overlapping write requests. Reported-by: Slava Pestov Signed-off-by: Stefan Hajnoczi Reviewed-by: Eric Blake Reviewed-by: Benoit Canet --- block.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/block.c b/block.c index 9c5566b55b..cb670fd54d 100644 --- a/block.c +++ b/block.c @@ -4553,6 +4553,12 @@ static int multiwrite_merge(BlockDriverState *bs, BlockRequest *reqs, // Add the second request qemu_iovec_concat(qiov, reqs[i].qiov, 0, reqs[i].qiov->size); + // Add tail of first request, if necessary + if (qiov->size < reqs[outidx].qiov->size) { + qemu_iovec_concat(qiov, reqs[outidx].qiov, qiov->size, + reqs[outidx].qiov->size - qiov->size); + } + reqs[outidx].nb_sectors = qiov->size >> 9; reqs[outidx].qiov = qiov; -- 2.30.2