Re: [PATCH v2 07/11] block: add x-blockdev-amend qmp command

From: Max Reitz <mreitz@redhat.com>
To: Maxim Levitsky <mlevitsk@redhat.com>, qemu-devel@nongnu.org
Cc: "Kevin Wolf" <kwolf@redhat.com>,
	"Daniel P. Berrangé" <berrange@redhat.com>,
	qemu-block@nongnu.org, "Markus Armbruster" <armbru@redhat.com>,
	"John Snow" <jsnow@redhat.com>
Subject: Re: [PATCH v2 07/11] block: add x-blockdev-amend qmp command
Date: Fri, 8 Nov 2019 11:36:51 +0100	[thread overview]
Message-ID: <4bcbb15d-4566-77a4-de0a-c9c3833543cc@redhat.com> (raw)
In-Reply-To: <268fd0b724a685b69e2d41067e34e403b68e244e.camel@redhat.com>

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On 08.11.19 10:26, Maxim Levitsky wrote:
> On Fri, 2019-10-04 at 20:53 +0200, Max Reitz wrote:
>> On 13.09.19 00:30, Maxim Levitsky wrote:
>>> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
>>> ---
>>>  block/Makefile.objs       |   2 +-
>>>  block/amend.c             | 116 ++++++++++++++++++++++++++++++++++++++
>>>  include/block/block_int.h |  23 ++++++--
>>>  qapi/block-core.json      |  26 +++++++++
>>>  qapi/job.json             |   4 +-
>>>  5 files changed, 163 insertions(+), 8 deletions(-)
>>>  create mode 100644 block/amend.c

[...]

>>> +static int coroutine_fn blockdev_amend_run(Job *job, Error **errp)
>>> +{
>>> +    BlockdevAmendJob *s = container_of(job, BlockdevAmendJob, common);
>>> +    int ret;
>>> +
>>> +    job_progress_set_remaining(&s->common, 1);
>>> +    ret = s->bs->drv->bdrv_co_amend(s->bs, s->opts, s->force, errp);
>>> +    job_progress_update(&s->common, 1);
>>
>> It would be nice if the amend job could make use of the progress
>> reporting that we have in place for amend.
> 
> I also thought about it, but is it worth it?
> 
> I looked through the status reporting of the qcow2 amend
> code (which doesn't really allowed to be run through
> qmp blockdev-amend, due to complexity of changing 
> the qcow2 format on the fly).

True, and we could always add it later.

I suppose I was mostly wondering because bdrv_amend_options already has
all of that infrastructure and I was assuming that qcow2's bdrv_co_amend
implementation would make some use of the existing function.  Well, it
doesn’t, so *shrug*

[...]

>>> +    /*
>>> +     * Create the block job
>>> +     * TODO Running in the main context. Block drivers need to error out or add
>>> +     * locking when they use a BDS in a different AioContext.
>>
>> Why shouldn’t the job just run in the node’s context?
> 
> This is shameless copy&pasta from the blockdev-create code
> (which I did note in the copyright of the file)
Well, you noted that it’s heavily based on it, not that it’s just C&P.

So I suppose the comment is just wrong here?

Max

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