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Re: [Qemu-devel] [PATCH v2 4/5] backdoor: [softmmu] Add QEMU-side proxy

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH v2 4/5] backdoor: [softmmu] Add QEMU-side proxy to "libbackdoor.a"
Date: Tue, 06 Dec 2011 16:35:38 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110831 Lightning/1.0b2 Thunderbird/3.1.13

On 12/06/2011 04:30 PM, Lluís Vilanova wrote:
Anthony Liguori writes:

I really worry about us introducing so many of these one-off paravirtual 
I would much prefer that you look at doing this as an extension to the ivshmem
device as it already has this sort of scope.  You should be able to do this by
just extending the size of bar 1 and using a well known guest id.

I did in fact look at ivshmem some time ago, and it's true that both use the
same mechanisms; but each device has a completely different purpose. To me it
just seems that extending the control BAR in ivshmem to call the user-provided
backdoor callbacks is just conflating two completely separate devices into a
single one. Besides, I think that the qemu-side of the backdoor is simple enough
to avoid being a maintenance burden.

They have the same purpose (which are both vague TBH). The only reason I'm sympathetic to this device is that virtio-serial has such insane semantics.

It's bad enough we already have two "backdoor" mechanisms, adding a third seems insane to me.


Anthony Liguori

Another question would be to join both so that the backdoor can be used to
orchestrate operations between multiple VMs through ivshmem's server, but I
really have no time to look into that and don't even know whether it would then
make sense to join both devices.


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