From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49673) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XKNbB-0006gv-4D for qemu-devel@nongnu.org; Thu, 21 Aug 2014 04:20:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XKNb4-00049J-UV for qemu-devel@nongnu.org; Thu, 21 Aug 2014 04:19:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:26222) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XKNb4-00049E-Lm for qemu-devel@nongnu.org; Thu, 21 Aug 2014 04:19:50 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id s7L8JnDN015788 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK) for ; Thu, 21 Aug 2014 04:19:50 -0400 Date: Thu, 21 Aug 2014 10:19:46 +0200 From: Kevin Wolf Message-ID: <20140821081946.GC4452@noname.redhat.com> References: <1405117387-25539-1-git-send-email-mreitz@redhat.com> <1405117387-25539-2-git-send-email-mreitz@redhat.com> <20140820114059.GF6122@noname.redhat.com> <53F4F36D.8070905@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53F4F36D.8070905@redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/4] block: Correct bs->growable List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Max Reitz Cc: qemu-devel@nongnu.org, Stefan Hajnoczi , armbru@redhat.com Am 20.08.2014 um 21:13 hat Max Reitz geschrieben: > On 20.08.2014 13:40, Kevin Wolf wrote: > >Am 12.07.2014 um 00:23 hat Max Reitz geschrieben: > >>Currently, the field "growable" in a BDS is set iff the BDS is opened in > >>protocol mode (with O_BDRV_PROTOCOL). However, not every protocol block > >>driver allows growing: NBD, for instance, does not. On the other hand, > >>a non-protocol block driver may allow growing: The raw driver does. > >> > >>Fix this by correcting the "growable" field in the driver-specific open > >>function for the BDS, if necessary. > >> > >>Signed-off-by: Max Reitz > >I'm not sure I agree with bs->growable = true for raw. It's certainly > >true that the backend can technically provide the functionality that > >writes beyond EOF grow the file. That's not the point of bs->growable, > >though. > > > >The point of it was to _forbid_ it to grow even when it's technically > >possible (non-file protocols weren't really a thing back then, apart > >from vvfat, so the assumption was that it's always technically > >possible). growable was introduced with bdrv_check_request(), which is > >supposed to reject guest requests after the end of the virtual disk (and > >this fixed a CVE, see commit 71d0770c). You're now disabling this check > >for raw. > > > >I think we need to make sure that bs->growable is only set if it is > >opened for an image that has drv->requires_growing_file set and > >therefore not directly used by a guest. > > > >Well, except that with node-name a guest will be able to use any image > >in the chain... Might this mean that it's really a BlockBackend > >property? > > I guess I can make things easy for me by just introducing some > "really_growable" or "writes_beyond_eof" field or something for the > sake of this series. ;-) Nah, don't evade the real solution... Using BDRV_O_PROTOCOL like we currently do isn't quite right either. If you clear growable when requires_growing_file isn't set for the parent, you should be fine. I think. Or hope. Kevin