From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53405) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W140l-0003p8-Lb for qemu-devel@nongnu.org; Wed, 08 Jan 2014 20:02:20 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1W140g-0004EK-Vk for qemu-devel@nongnu.org; Wed, 08 Jan 2014 20:02:15 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58908) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W140g-0004EB-MC for qemu-devel@nongnu.org; Wed, 08 Jan 2014 20:02:10 -0500 Message-ID: <52CDF500.6080901@redhat.com> Date: Thu, 09 Jan 2014 09:01:52 +0800 From: Fam Zheng MIME-Version: 1.0 References: <1389210205-10787-1-git-send-email-peter@gridcentric.ca> In-Reply-To: <1389210205-10787-1-git-send-email-peter@gridcentric.ca> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH] block: fix backing file segfault List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Feiner , qemu-devel@nongnu.org Cc: kwolf@redhat.com Hi Peter, Thank your for catching this. On 2014=E5=B9=B401=E6=9C=8809=E6=97=A5 03:43, Peter Feiner wrote: > 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=3Dbase.file\ > file-overlay.qcow2 > ./qemu-img convert -O raw file-overlay.qcow2 file-convert.raw > > echo Test nbd format > SOCK=3D$PWD/nbd.sock > ./qemu-img create -f raw base.raw 1m > ./qemu-nbd -t -k $SOCK base.raw & > trap "kill $!" EXIT > while ! test -e $SOCK; do sleep 1; done > ./qemu-img create -f qcow2 -F nbd -o backing_file=3Dnbd:unix:$SOCK= \ > nbd-overlay.qcow2 > ./qemu-img convert -O raw nbd-overlay.qcow2 nbd-convert.raw It would be nice if you can add this as a test case under=20 tests/qemu-iotests. > > 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); Braces are mandatory for if statements (scripts/checkpatch.pl can check=20 the coding style for you). Thanks, Fam