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Date: Thu, 14 Jul 2011 11:00:40 +0100
Message-ID: <CAJSP0QXOA-qvWegnfYOHS7BnUNDS811r467ogN825ZyDJ0Hf1A@mail.gmail.com>
From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] live block copy/stream/snapshot discussion
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To: Kevin Wolf <kwolf@redhat.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, Dor Laor <dlaor@redhat.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, Marcelo Tosatti <mtosatti@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, Avi Kivity <avi@redhat.com>, Adam Litke <agl@us.ibm.com>

On Thu, Jul 14, 2011 at 10:55 AM, Kevin Wolf <kwolf@redhat.com> wrote:
> Am 14.07.2011 11:39, schrieb Stefan Hajnoczi:
>> =A0Events:
>>
>> =A0On completion the BLOCK_STREAM_COMPLETED event is raised with the fol=
lowing
>> =A0fields:
>>
>> =A0- device: device name (json-string)
>> =A0- len: =A0 =A0size of the device, in bytes (json-int)
>> =A0- offset: last offset of completed I/O, in bytes (json-int)
>> =A0- error: =A0error message (json-string, only on error)
>>
>> =A0The completion event is raised both on success and on failure.
>
> Why do len/offset matter in a completion event?

For completeness.  You could see it as telling you how much progress
was made before an error occurred.  In the success case offset will
always be equal to len.  But in the error case you get the last
completed progress before error, which could be useful (for example if
you weren't polling but want to display "Streaming virtio-blk0 failed
at 33%").

Stefan