Re: [Qemu-devel] [PATCH v2 4/5] backdoor: [softmmu] Add QEMU-side proxy to "libbackdoor.a"

[Anthony Liguori <anthony@codemonkey.ws>]

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 devices.
>> 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.

Regards,

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.
>
>
> Thanks,
>    Lluis
>