From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49769) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W0z2Q-0006eX-Cw for qemu-devel@nongnu.org; Wed, 08 Jan 2014 14:43:44 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1W0z2K-0008Nn-BF for qemu-devel@nongnu.org; Wed, 08 Jan 2014 14:43:38 -0500 Received: from mail-ie0-f169.google.com ([209.85.223.169]:37761) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W0z2K-0008Nc-6l for qemu-devel@nongnu.org; Wed, 08 Jan 2014 14:43:32 -0500 Received: by mail-ie0-f169.google.com with SMTP id e14so2554620iej.28 for ; Wed, 08 Jan 2014 11:43:31 -0800 (PST) From: Peter Feiner Date: Wed, 8 Jan 2014 19:43:25 +0000 Message-Id: <1389210205-10787-1-git-send-email-peter@gridcentric.ca> Subject: [Qemu-devel] [PATCH] block: fix backing file segfault List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: kwolf@redhat.com, Peter Feiner , famz@redhat.com When a backing file is opened such that (1) a protocol is directly used as the block driver and (2) the block driver has bdrv_file_open, bdrv_open_backing_file segfaults. The problem arises because bdrv_open_common returns without setting bd->backing_hd->file. To effect (1), you seem to have to use the -F flag in qemu-img. There are several block drivers that satisfy (2), such as "file" and "nbd". Here are some concrete examples: #!/bin/bash echo Test file format ./qemu-img create -f file base.file 1m ./qemu-img create -f qcow2 -F file -o backing_file=base.file\ file-overlay.qcow2 ./qemu-img convert -O raw file-overlay.qcow2 file-convert.raw echo Test nbd format SOCK=$PWD/nbd.sock ./qemu-img create -f raw base.raw 1m ./qemu-nbd -t -k $SOCK base.raw & trap "kill $!" EXIT while ! test -e $SOCK; do sleep 1; done ./qemu-img create -f qcow2 -F nbd -o backing_file=nbd:unix:$SOCK\ nbd-overlay.qcow2 ./qemu-img convert -O raw nbd-overlay.qcow2 nbd-convert.raw Without this patch, the two qemu-img convert commands segfault. This is a regression that was introduced in v1.7 by dbecebddfa4932d1c83915bcb9b5ba5984eb91be. Signed-off-by: Peter Feiner --- block.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/block.c b/block.c index 64e7d22..a4a172d 100644 --- a/block.c +++ b/block.c @@ -1016,8 +1016,9 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp) error_free(local_err); return ret; } - pstrcpy(bs->backing_file, sizeof(bs->backing_file), - bs->backing_hd->file->filename); + if (bs->backing_hd->file) + pstrcpy(bs->backing_file, sizeof(bs->backing_file), + bs->backing_hd->file->filename); return 0; } -- 1.7.9.5