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Date: Thu, 18 Apr 2013 15:41:20 +0800
From: Liu Yuan <namei.unix@gmail.com>
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Subject: Re: [Qemu-devel] [PATCH v7] sheepdog: add discard/trim support for
 sheepdog
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, sheepdog@lists.wpkg.org, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>

On 04/18/2013 03:37 PM, Stefan Hajnoczi wrote:
>> @@ -184,6 +186,8 @@ typedef struct SheepdogInode {
>> >      uint32_t data_vdi_id[MAX_DATA_OBJS];
>> >  } SheepdogInode;
>> >  
>> > +static bool discard_supported = true;
> Normally state should be part of BDRVSheepdogState so that it does not
> affect other sheepdog drives.
> 
> Please confirm that all -drive file=sheepdog:... must either support
> discard or not support it.  I asked this in an older version of the
> patch but wasn't sure if my question was clear.
> 

Ah, I see, this time I got your question clearly.

> Imagine a scenario where you run two sheepdog clusters and want to
> connect one drive from each cluster to your VM.  If one cluster uses
> outdated sheepdog software but the other is up-to-date, then it should
> still be possible to use discard on the up-to-date cluster.

Makes sense. I'll use a per structure enabler.

Thanks,
Yuan