Re: [Qemu-devel] [PATCH v5 1/6] Stream block job involves copy-on-read filter driver

[Max Reitz <mreitz@redhat.com>]

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On 08.01.19 14:45, Vladimir Sementsov-Ogievskiy wrote:
> 30.12.2018 23:09, Andrey Shinkevich wrote:
>> The copy-on-read filter is applied to block-stream operation.
>> It is necessary for further block discard option.
> 
> If we move to c-o-r filter in stream, I think we should:
> 1. get rid of COPY_ON_READ flag in stream code (so, this thing to be done in one place)
> 2. add base parameter to c-o-r filter, to not copy things that are below base.
> 
> Current behavior of stream is enabling copy-on-read on bs during stream if base == NULL.
> So, if we just add c-o-r filter, we will copy extra blocks. On the other hand, if we
> support base parameter in c-o-r filter we will involve guest reads to the stream
> process for cases with base != NULL, so stream operation should become more efficient.
> 
> So for me the following sequence seems reasonable:
> 
> - prepare iotests for graph changes
> - add base parameter to c-o-r filter
> - use c-o-r in stream and drop COPY_ON_READ flag from stream code
> 
> then (may be in separate series) add discard functionality. And looks like again, it should
> be property of c-o-r filter, not stream job itself, to involve guest reads to discarding too.
> 
> In general, Max, is that correspond to what you mean?

Yep, that sounds good to me.

Max


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