From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=36939 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PnYmU-0000fQ-Hf for qemu-devel@nongnu.org; Thu, 10 Feb 2011 10:50:07 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PnYmL-00084E-Jv for qemu-devel@nongnu.org; Thu, 10 Feb 2011 10:49:59 -0500 Received: from mx1.redhat.com ([209.132.183.28]:61892) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PnYmL-00083k-DC for qemu-devel@nongnu.org; Thu, 10 Feb 2011 10:49:57 -0500 From: Kevin Wolf Date: Thu, 10 Feb 2011 16:51:26 +0100 Message-Id: <1297353086-4844-12-git-send-email-kwolf@redhat.com> In-Reply-To: <1297353086-4844-1-git-send-email-kwolf@redhat.com> References: <1297353086-4844-1-git-send-email-kwolf@redhat.com> Subject: [Qemu-devel] [PATCH 11/11] qcow2: Fix order in L2 table COW List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: anthony@codemonkey.ws Cc: kwolf@redhat.com, qemu-devel@nongnu.org When copying L2 tables (this happens only with internal snapshots), the order wasn't completely safe, so that after a crash you could end up with a L2 table that has too low refcount, possibly leading to corruption in the long run. This patch puts the operations in the right order: First allocate the new L2 table and replace the reference, and only then decrease the refcount of the old table. Signed-off-by: Kevin Wolf --- block/qcow2-cluster.c | 9 ++++++--- 1 files changed, 6 insertions(+), 3 deletions(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 437aaa8..750abe3 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -515,13 +515,16 @@ static int get_cluster_table(BlockDriverState *bs, uint64_t offset, return ret; } } else { - /* FIXME Order */ - if (l2_offset) - qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t)); + /* First allocate a new L2 table (and do COW if needed) */ ret = l2_allocate(bs, l1_index, &l2_table); if (ret < 0) { return ret; } + + /* Then decrease the refcount of the old table */ + if (l2_offset) { + qcow2_free_clusters(bs, l2_offset, s->l2_size * sizeof(uint64_t)); + } l2_offset = s->l1_table[l1_index] & ~QCOW_OFLAG_COPIED; } -- 1.7.2.3