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From: Peter Lieven <pl@kamp.de>
To: Kevin Wolf <kwolf@redhat.com>, Max Reitz <mreitz@redhat.com>
Cc: famz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com,
	armbru@redhat.com
Subject: Re: [Qemu-devel] [PATCH] block: add a knob to disable multiwrite_merge
Date: Mon, 20 Oct 2014 15:47:31 +0200	[thread overview]
Message-ID: <54451273.8040007@kamp.de> (raw)
In-Reply-To: <20141020133100.GJ3585@noname.redhat.com>

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?

Peter

  reply	other threads:[~2014-10-20 13:47 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-20  6:14 [Qemu-devel] [PATCH] block: add a knob to disable multiwrite_merge Peter Lieven
2014-10-20  8:59 ` Max Reitz
2014-10-20  9:14   ` Peter Lieven
2014-10-20  9:27     ` Max Reitz
2014-10-20 10:03       ` Peter Lieven
2014-10-20 11:51         ` Max Reitz
2014-10-20 11:53           ` Peter Lieven
2014-10-20 12:56             ` Kevin Wolf
2014-10-20 12:16           ` Peter Lieven
2014-10-20 12:19             ` Max Reitz
2014-10-20 12:48               ` Peter Lieven
2014-10-20 13:15                 ` Max Reitz
2014-10-20 13:19                   ` Peter Lieven
2014-10-20 13:22                     ` Max Reitz
2014-10-20 13:29                       ` Peter Lieven
2014-10-20 13:31                       ` Kevin Wolf
2014-10-20 13:47                         ` Peter Lieven [this message]
2014-10-20 13:55                           ` Kevin Wolf
2014-10-20 13:59                             ` Peter Lieven
2014-10-20 13:59                               ` Max Reitz

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