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[Qemu-devel] Re: KVM call agenda for Apr 27

From: Dor Laor
Subject: [Qemu-devel] Re: KVM call agenda for Apr 27
Date: Tue, 27 Apr 2010 12:32:49 +0300
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On 04/27/2010 12:22 PM, Avi Kivity wrote:
On 04/27/2010 12:08 PM, Dor Laor wrote:
On 04/27/2010 11:56 AM, Avi Kivity wrote:
On 04/27/2010 11:48 AM, Dor Laor wrote:
Here's another option: an nbd-like protocol that remotes all
operations except read and write over a unix domain socket. The open
operation returns an fd (SCM_RIGHTS strikes again) that is used for
and write. This can be used to implement snapshots over LVM, for

Why w/o read/writes?

To avoid the copying.

Of course, just pass the offset+len on read/write too

There will be a large performance impact.

IMHO the whole thing is way over engineered:
a) Having another channel into qemu is complicating management
software. Isn't the monitor should be the channel? Otherwise we'll
need to create another QMP (or nbd like Avi suggest) for these
actions. It's extra work for mgmt and they will have hard time to
understand events interleaving of the various channels

block layer plugins allow intercepting all interesting block layer
events, not just write-past-a-watermark, and allow actions based on
those events. It's a more general solution.

No problem there, as long as we do try to use the single existing QMP
with the plugins. Otherwise we'll create QMP2 for the block events in
a year from now.

I don't see how we can interleave messages from the plugin into the qmp
stream without causing confusion.

Those are QMP async events.

Since Kevin suggested adding even more events (was is cynical?) maybe we can use optional QMP opaque block events that the plugin issues and it will travel using the standard QMP connection as async event to the interested mgmt app.
Once stabilized each event can go into the official QMP protocol.

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