From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40702) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XC6ir-0006g2-NJ for qemu-devel@nongnu.org; Tue, 29 Jul 2014 08:41:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XC6il-0001my-IA for qemu-devel@nongnu.org; Tue, 29 Jul 2014 08:41:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:11417) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XC6il-0001lo-AB for qemu-devel@nongnu.org; Tue, 29 Jul 2014 08:41:35 -0400 From: Stefan Hajnoczi Date: Tue, 29 Jul 2014 13:41:25 +0100 Message-Id: <1406637686-25762-2-git-send-email-stefanha@redhat.com> In-Reply-To: <1406637686-25762-1-git-send-email-stefanha@redhat.com> References: <1406637686-25762-1-git-send-email-stefanha@redhat.com> Subject: [Qemu-devel] [PATCH 1/2] block: fix overlapping multiwrite requests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Kevin Wolf , andrey@xdel.ru, sviatoslav.pestov@gmail.com When request A is a strict subset 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 --- block.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/block.c b/block.c index 8cf519b..0a3ac43 100644 --- a/block.c +++ b/block.c @@ -4498,6 +4498,12 @@ 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; -- 1.9.3