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Date: Wed, 31 Oct 2012 14:01:00 +0100
From: Christoph Hellwig <hch@lst.de>
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Subject: Re: [Qemu-devel] [PATCH v2 8/9] qmp: add NBD server commands
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, lcapitulino@redhat.com, Christoph Hellwig <hch@lst.de>, qemu-devel@nongnu.org

On Wed, Oct 31, 2012 at 01:46:22PM +0100, Paolo Bonzini wrote:
> qemu-nbd does support AIO in the latest versions.  There's also
> --cache=MODE and --aio=MODE command-line options.

Oh true, it's just hidden behind coroutines.  With --aio-native and
--nocache I actually get fairly reasonable performance out of it now.

> But if you need a QMP interface, adding it to qemu-nbd would really be a
> bad idea. :)

I don't nessecarily need QMP, I'm just looking for a way to create a
snapshot underneath an exported image.

> You can use qtest mode to get very close to this (even if you send
> stop/cont by mistake on the monitor, no code will actually run):
> 
> qemu-system-x86_64 -chardev file,id=null,path=/dev/null -qtest null
> -machine accel=qtest -m 1 -nodefaults -nographic
> 
> but having a separate do-nothing target would probably be nicer...
> though Anthony may have different opinions.

That looks fairlt reasonable, thanks.