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[Qemu-devel] Re: [PATCH] monitor: Add port write command

From: Anthony Liguori
Subject: [Qemu-devel] Re: [PATCH] monitor: Add port write command
Date: Tue, 14 Jul 2009 10:49:08 -0500
User-agent: Thunderbird (X11/20090320)

Juan Quintela wrote:
We were thinking about that functionality some time ago.  We were
looking at an apic bug during migration, and it was not trivial to dump
apic state before and after migration.

I took a look at it, and basically decided that I would have to
replicate the savevm method.  Your apprearch mean that doing the command
is trivial, and we have "meaningful" labels for it.

Will take a look at using that in some driver.

Great. I think an incremental conversion is the right approach. If we tie this into qdev correctly, then we could also do some nice things with migration. We could dump out a file that describes any given migration protocol version. We could then use this to automatically check whether we broke the migration format between versions but just doing a diff.

I think there's also an opportunity to adjust the migration protocol. One change I had to make to the savevm format was removing all of the size parameters. This is because the nature of QEMUFile makes it such that you don't know what the size was until you actually wrote data. The old savevm format used to rely on seeking to update the size parameter. If we know the size of the section (based on the description), we can reintroduce this to the protocol.

What's more, we can probably get rid of QEMUFile all together and introduce a more useful abstraction that doesn't have such complex buffering.

This refactoring is definitely high on my 0.12 wish list :-)


Anthony Liguori

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