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

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [Qemu-block] [PATCH v5 1/6] Stream block job involves copy-on-read filter driver
Date: Tue, 8 Jan 2019 13:45:31 +0000

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 

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?

Any suggestions?

Best regards,

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