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Re: [Qemu-devel] [PATCH v4 13/13] block/mirror: Block "device IO" during

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v4 13/13] block/mirror: Block "device IO" during mirror exit
Date: Tue, 19 May 2015 10:49:41 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 19/05/2015 18:48, Fam Zheng wrote:
>> > 
>> > This is too late.  As a rule, the blocker must be established before
>> > calling bdrv_drain, and removed on the next yield (in this case, before
>> > the assignment to last_pause_ns).
> I don't understand. If the blocker is removed before mirror_run returns,
> wouldn't more device IO already hit source image by the time mirror_exit runs?

If you go to mirror_exit, you won't reach the assignment (so you have to
remove the blocker in mirror_exit too).

But if you don't go to mirror_exit because cnt != 0, you must remove the
blocker before the next I/O.


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