From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35364) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XgDUX-0000op-89 for qemu-devel@nongnu.org; Mon, 20 Oct 2014 09:59:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XgDUR-00088N-2D for qemu-devel@nongnu.org; Mon, 20 Oct 2014 09:59:21 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:34255 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XgDUQ-00087S-M3 for qemu-devel@nongnu.org; Mon, 20 Oct 2014 09:59:14 -0400 Message-ID: <54451524.5070709@kamp.de> Date: Mon, 20 Oct 2014 15:59:00 +0200 From: Peter Lieven MIME-Version: 1.0 References: <5444DDF4.40800@kamp.de> <5444F730.4000003@redhat.com> <5444FD07.6030702@kamp.de> <5444FDBE.9060501@redhat.com> <54450491.7060506@kamp.de> <54450AD7.8000901@redhat.com> <54450BED.6000101@kamp.de> <54450C9A.8040807@redhat.com> <20141020133100.GJ3585@noname.redhat.com> <54451273.8040007@kamp.de> <20141020135556.GK3585@noname.redhat.com> In-Reply-To: <20141020135556.GK3585@noname.redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] block: add a knob to disable multiwrite_merge List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: armbru@redhat.com, famz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, Max Reitz On 20.10.2014 15:55, Kevin Wolf wrote: > Am 20.10.2014 um 15:47 hat Peter Lieven geschrieben: >> On 20.10.2014 15:31, Kevin Wolf wrote: >>> Am 20.10.2014 um 15:22 hat Max Reitz geschrieben: >>>> On 20.10.2014 at 15:19, Peter Lieven wrote: >>>>> On 20.10.2014 15:15, Max Reitz wrote: >>>>>> On 20.10.2014 at 14:48, Peter Lieven wrote: >>>>>>> On 20.10.2014 14:19, Max Reitz wrote: >>>>>>>> On 2014-10-20 at 14:16, Peter Lieven wrote: >>>>>>>>> On 20.10.2014 13:51, Max Reitz wrote: >>>>>>>>>> On 2014-10-20 at 12:03, Peter Lieven wrote: >>>>>>>>>> [...] >>>>>>>>> Can you further help here. I think my problem was that I >>>>>>>>> don't have access to the commandline options in >>>>>>>>> bdrv_open?! >>>>>>>> You do. It's the "options" QDict. :-) >>>>>>> Maybe I just don't get it. >>>>>>> >>>>>>> If I specify >>>>>>> >>>>>>> qemu -drive if=virtio,file=image.qcow2,write-merging=off >>>>>>> >>>>>>> and check with >>>>>>> >>>>>>> qdict_get_try_bool(options, "write-merging", true); >>>>>>> >>>>>>> in bdrv_open() directly before bdrv_swap I always get true. >>>>>> Hm, judging from fprintf(stderr, "%s\n", >>>>>> qstring_get_str(qobject_to_json_pretty(QOBJECT(options))));, >>>>>> it's there for me (directly after qdict_del(options, >>>>>> "node-name"). The output is: >>>>>> >>>>>> Qemu wrote: >>>>>>> { >>>>>>> "filename": "image.qcow2" >>>>>>> } >>>>>>> { >>>>>>> "write-merging": "off" >>>>>>> } >>>>>>> qemu-system-x86_64: -drive >>>>>>> if=virtio,file=image.qcow2,write-merging=off: could not open >>>>>>> disk image image.qcow2: Block format 'qcow2' used by device >>>>>>> 'virtio0' doesn't support the option 'write-merging' >>>>>> But as you can see, it's a string and not a bool. So the problem >>>>>> is that there are (at least) two parameter "types" in qemu: One >>>>>> is just giving a QDict, and the other are QemuOpts. QDicts are >>>>>> just the raw user input and the user can only input strings, so >>>>>> everything is just a string. As far as I know, typing everything >>>>>> correctly is done by converting the QDict to a QemuOpts object >>>>>> (as you can see in generally every block driver which supports >>>>>> some options (e.g. qcow2) and also in blockdev_init(), it's >>>>>> qemu_opts_absorb_qdict()). >>>>>> >>>>>> Sooo, right, I forgot that. Currently, there are no non-string >>>>>> non-block-driver-specific options for mid-tree BDS (in contrast >>>>>> to the root BDS, which are parsed in blockdev_init()), so you >>>>>> now have the honorable task of introducing such a QemuOptsList >>>>>> along with qemu_opts_absorb_qdict() and everything to >>>>>> bdrv_open_common(). *cough* >>>>> I would appreciate if someone with better knowledge of this whole >>>>> stuff would start this. Or we postpone this know until all the >>>>> ongoing conversions are done. >>>> I can try and create some barebone which your patches can then be >>>> based on. I probably don't have the knowledge either, but I'm daring >>>> enough to do it anyway. ;-) >>> Actually I have some patches somewhere [1] that introduce a QemuOpts for >>> bdrv_open_common(). I intended to use that for cache modes, but as I >>> explained in our KVM Forum presentation, it's not quite as easy as I >>> thought it would be and so the patch series isn't ready yet. >>> >>> Anyway, having the QemuOpts there for driver-independent options is >>> probably the way to go. Feel free to remove the caching from my >>> patch and keep only the node-name part. Then it can be a preparatory >>> patch for your series where you simply add a new option to the list. >>> >>> Kevin >>> >>> [1] http://repo.or.cz/w/qemu/kevin.git/commitdiff/9c22aee04cf0bdf6a3858340bc6ff27d6805254f >> Thank you. >> >> Would it be legit to recycle qemu_common_drive_opts from blockdev.c for this? > No, I don't think so. That one should in theory be only for BlockBackend > options. For the short term, it still mixes BB and BDS options, but BDS > options should be moved out step by step. In any case, it is only used > for the top level. > > Any option that is parsed with qemu_opts_absorb_qdict() in > bdrv_open_common() must also be handled there. If you don't ensure that > and extract all the options that blockdev_init() knows without actually > handling them, it can happen that invalid options are silently ignored > (e.g. backing.werror should error out, but would be accepted). > > And please coordinate with Max, if both of you write a patch, that's > wasted time. Max, if you don't have started I would use Kevins patch as basis? Peter