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Date: Thu, 05 Jun 2014 13:26:56 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/3] mirror: Go through ready -> complete
 process for 0 len image
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To: Stefan Hajnoczi <stefanha@gmail.com>, Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, jcody@redhat.com, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Max Reitz <mreitz@redhat.com>

Il 05/06/2014 13:17, Stefan Hajnoczi ha scritto:
> On Thu, Jun 05, 2014 at 11:42:34AM +0800, Fam Zheng wrote:
>> diff --git a/block/mirror.c b/block/mirror.c
>> index 94c8661..2bef5f3 100644
>> --- a/block/mirror.c
>> +++ b/block/mirror.c
>> @@ -324,9 +324,18 @@ static void coroutine_fn mirror_run(void *opaque)
>>      }
>>
>>      s->common.len = bdrv_getlength(bs);
>> -    if (s->common.len <= 0) {
>> +    if (s->common.len < 0) {
>>          ret = s->common.len;
>>          goto immediate_exit;
>> +    } else if (s->common.len == 0) {
>> +        /* Report BLOCK_JOB_READY and wait for complete. */
>> +        block_job_ready(&s->common);
>> +        s->synced = true;
>> +        while (!block_job_is_cancelled(&s->common) && !s->should_complete) {
>> +            block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, SLICE_TIME);
>
> Please take a look at block_job_resume() and how it's used when
> cancelling or completing block jobs.  There is no need to sleep, instead
> we can yield until we get resumed.
>

You still need to set job->busy = false.  So I guess we need a new 
function block_job_yield.

Paolo