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From: Paolo Bonzini <pbonzini@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>
Cc: John Snow <jsnow@redhat.com>, qemu-devel <qemu-devel@nongnu.org>,
	stefanha@redhat.com, wangxiaolong@ucloud.cn
Subject: Re: [Qemu-devel] Fwd: qemu drive mirror assert fault
Date: Tue, 05 May 2015 13:54:27 +0200	[thread overview]
Message-ID: <5548AF73.3070901@redhat.com> (raw)
In-Reply-To: <5548AE65.2050405@redhat.com>



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
> 
> 

  reply	other threads:[~2015-05-05 11:54 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <tencent_D4C0F8C0FE9E16802F5FF410@qq.com>
2015-04-30 15:50 ` [Qemu-devel] Fwd: qemu drive mirror assert fault Paolo Bonzini
2015-04-30 15:54   ` Paolo Bonzini
2015-05-05  7:36   ` Fam Zheng
2015-05-05 10:13     ` Paolo Bonzini
2015-05-05 10:27       ` Fam Zheng
2015-05-05 11:48         ` Kevin Wolf
2015-05-05 11:49           ` Paolo Bonzini
2015-05-05 11:54             ` Paolo Bonzini [this message]
2015-05-05 13:03             ` Kevin Wolf
2015-05-05 13:07               ` Paolo Bonzini
2015-05-05 13:31                 ` Kevin Wolf
2015-05-05 12:09           ` Fam Zheng

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