From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41617) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cVdoJ-0005AE-08 for qemu-devel@nongnu.org; Mon, 23 Jan 2017 07:33:23 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cVdoI-0006UX-4O for qemu-devel@nongnu.org; Mon, 23 Jan 2017 07:33:23 -0500 From: Fam Zheng Date: Mon, 23 Jan 2017 20:30:55 +0800 Message-Id: <20170123123056.30383-16-famz@redhat.com> In-Reply-To: <20170123123056.30383-1-famz@redhat.com> References: <20170123123056.30383-1-famz@redhat.com> Subject: [Qemu-devel] [PATCH v12 15/16] qcow2: Force "no other writer" lock on bs->file List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: "Daniel P. Berrange" , qemu-block@nongnu.org, eblake@redhat.com, Kevin Wolf , rjones@redhat.com, Max Reitz Writing to the same qcow2 file from two QEMU processes at the same time will never work correctly, so disable it even when the caller specifies BDRV_O_RDWR. Other formats are less vulnerable because they don't have internal snapshots thus qemu-img is less often misused to create live snapshot. Signed-off-by: Fam Zheng --- block/qcow2.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/block/qcow2.c b/block/qcow2.c index 96fb8a8..879361a 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -1177,6 +1177,17 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags, } } + if ((flags & BDRV_O_SHARE_RW) && (flags & BDRV_O_RDWR)) { + /* Shared write is never a good idea for qcow2, override it. + * XXX: Use permission propagation and masking mechanism in op blockers + * API once it's there. */ + ret = bdrv_reopen(bs->file->bs, flags & ~BDRV_O_SHARE_RW, &local_err); + if (ret) { + error_propagate(errp, local_err); + goto fail; + } + } + #ifdef DEBUG_ALLOC { BdrvCheckResult result = {0}; -- 2.9.3