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Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Int

From: Wolfgang Richter
Subject: Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection
Date: Tue, 14 May 2013 15:30:59 -0400

On Tue, May 14, 2013 at 12:45 PM, Paolo Bonzini <address@hidden> wrote:
No, I'll just reuse the same hooks within block/mirror.c (almost... it
looks like I need after_write too, not just before_write :( that's a
pity).  Basically:

1) before the write, if there is space in the job's buffers, allocate a
MirrorOp and a data buffer for the write.  Also record whether the block
was dirty before;

2) after the write, do nothing if there was no room to allocate the data
buffer.  Else clear the block from the dirty bitmap.  If the block was
dirty, read the whole cluster from the source as in passive mirroring.
If it wasn't, copy the data from guest memory to the preallocated buffer
and write it to the destination;

> If I knew more about what you
> had in mind, I wouldn't mind trying to add this 'active' mode to
> 'drive-mirror'
> and test it with my use case.  I want to avoid duplicate work, so if you
> want to implement it yourself I can defer this.

Also the other way round.  If you want to give it a shot based on the
above spec just tell me.

Talked with my group here as well.  I think I'd like to give it a shot based on the
above spec rather than refactor my code into a new command.  This way it will
hopefully reduce duplicated efforts, and provide extra testing for the "active
mirroring" code.

I'll take a pass through the mirror code to make sure I understand it better than
I currently do.

Would you like to coordinate off-list until we have a patch?


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