From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45709) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W1DKt-0007Tc-DF for qemu-devel@nongnu.org; Thu, 09 Jan 2014 05:59:44 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1W1DKo-0006jo-HS for qemu-devel@nongnu.org; Thu, 09 Jan 2014 05:59:39 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52997) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W1DKo-0006jk-84 for qemu-devel@nongnu.org; Thu, 09 Jan 2014 05:59:34 -0500 Date: Thu, 9 Jan 2014 11:59:30 +0100 From: Kevin Wolf Message-ID: <20140109105930.GA2862@dhcp-200-207.str.redhat.com> References: <1389210205-10787-1-git-send-email-peter@gridcentric.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1389210205-10787-1-git-send-email-peter@gridcentric.ca> 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 Cc: famz@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com [ CCing Max, who was recently active in this area, for another opinion ] Am 08.01.2014 um 20:43 hat Peter Feiner geschrieben: > 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; > } I think if there is no bs->backing_hd->file, we should get the filename from bs->backing_hd->filename instead of leaving it empty. In fact, can we always do that or does bs->backing_hd normally lack the filename? If so, perhaps that is what we need to fix, so we can always directly use bs->backing_hd->filename here. Kevin