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Date: Tue, 05 May 2015 13:54:27 +0200
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Subject: Re: [Qemu-devel] Fwd: qemu drive mirror assert fault
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To: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>
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On 05/05/2015 13:49, Paolo Bonzini wrote:
> 
> 
> On 05/05/2015 13:48, Kevin Wolf wrote:
>> It depends. In its basic form, bdrv_discard() just means "I don't care
>> about the data any more". Then clearing the dirty bitmap is correct.
>>
>> The content is only important if the caller used discard to write zeros
>> because can_write_zeroes_with_unmap = true. Do we have any such callers
>> apart from qemu-img convert?
> 
> Yes, the SCSI command WRITE SAME with UNMAP = 1 (not coincidentially :))
> calls discard too.

s/discard/write_zeroes/ of course!

Paolo

> Who knows what the guest used it for...
> However, write zeroes doesn't go through bdrv_co_discard, does it?
> 
> Paolo
> 
>