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Date: Thu, 23 Jun 2016 14:57:29 +0800
From: Changlong Xie <xiecl.fnst@cn.fujitsu.com>
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Subject: Re: [Qemu-devel] [PATCH 1/2] blockjob: assert(cb) in the entry
 functions of blockjob
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To: Kevin Wolf <kwolf@redhat.com>
Cc: Eric Blake <eblake@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, qemu devel <qemu-devel@nongnu.org>, Jeff Cody <jcody@redhat.com>, Fam Zheng <famz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Max Reitz <mreitz@redhat.com>

On 06/23/2016 02:21 PM, Kevin Wolf wrote:
> Am 23.06.2016 um 03:04 hat Changlong Xie geschrieben:
>> On 06/23/2016 01:31 AM, Eric Blake wrote:
>>> On 06/22/2016 04:19 AM, Paolo Bonzini wrote:
>>>>
>>>>
>>>> On 22/06/2016 12:12, Changlong Xie wrote:
>>>>>
>>>>> commit/mirror/stream/backup use block_job_create(..., cb,..) to create
>>>>> relevant blockjob. When they finished, these jobs will invoke
>>>>> block_job_completed, then invoke job->cb() unconditionally. So i think
>>>>> we need this to avoid segment fault. Actually backup has implemented this.
>>>>
>>>> So this suggests that the right place to put the assertion would be
>>>> block_job_create.  But it's even better to add a
>>>>
>>>> #define QEMU_NONNULL __attribute__((__nonnull__))
>>>>
>>>> to include/qemu/compiler.h and declare the arguments as non-null.
>>>
>>> Or alternatively fix things to only invoke job->cb() if it is non-NULL,
>>> so that callers don't have to pass in a no-op callback just to appease a
>>> non-NULL attribute.
>>
>> Is there any reason, that we should invoke job->cb() unconditionally
>> without nonnull check? There is no relevant clue in the historical
>> commit messages. If yes, i prefer paolo's suggestion; otherwise
>> eric's solution is better.
>
> I don't think no-op callbacks actually exist for jobs.
>

So, i'll put assert(cb) in block_job_create as Paolo suggested.

Thanks
	-Xie

> Kevin
>
>
> .
>