Re: [vmw_vmci RFC 00/11] VMCI for Linux

[Dor Laor <dlaor@redhat.com>]

On 06/06/2012 08:06 AM, Greg KH wrote:
> On Tue, Jun 05, 2012 at 12:02:51AM -0700, Dmitry Torokhov wrote:
>> Hi Greg,
>>
>> On Mon, Jun 04, 2012 at 03:57:57PM -0700, Greg KH wrote:
>>> On Fri, Jun 01, 2012 at 08:33:02AM -0700, Andy King wrote:
>>>> Greg,
>>>>
>>>> Thanks so much for the comments and apologies for the delayed response.
>>>>
>>>>> Don't we have something like this already for KVM and maybe Xen?
>>>>> virtio?  Can't you use that code instead of a new block of code that
>>>>> is only used by vmware users?  It has virtual pci devices which
>>>>> should give you what you want/need here, right?
>>>>>
>>>>> If not, why doesn't that work for you?  Would it be easier to just
>>>>> extend it?
>>>>
>>>> The VMCI virtual device for which this driver is intended has been
>>>> around a lot longer than this submission might suggest.  The virtual
>>>> hardware was released in a product before Rusty sent his RFC and
>>>> quite a bit before it made it to mainline; there was, regrettably,
>>>> no virtio then.
>>>>
>>>> As such, it was designed to be its own transport, and it's something
>>>> that is now very much fixed at the hardware level (enhancements
>>>> not withstanding), and which we have to support all the way back.
>>>
>>> What "hardware" are you refering to here?
>>
>> The virtual hardware that is currently shipping and has been shipping
>> for a few years.
>>
>>>
>>>> In addition to that, our hypervisor endpoints are written using
>>>> the existing device backend; virtio doesn't currently make a lot of
>>>> sense for them, and would require a lot of additional work.
>>>>
>>>> All of this is unfortunate.  While I agree that virtio is certainly
>>>> the right approach, and we need to avoid this proliferation, I think
>>>> at this point we'd really like to try and upstream this in its current
>>>> form.  There's certainly the possibility going forwards that we could
>>>> add a glue layer, such that other clients could use virtio if they're
>>>> willing to write their own hypervisor endpoints.
>>>>
>>>> Does that sound reasonable?
>>>
>>> Not really, why should we take an interface that is tied to something
>>> that you are saying isn't something we should be using?
>>
>> That is not what Andy said. If virtio was available when we started
>> shipping VMCI then we certainly could have used that, but since it
>> wasn't there we invented something else.
>
> Ok, that makes sense.
>
>>> Don't you also
>>> have control over the hypervisor side of things in order to properly
>>> design this type of thing?
>>
>> We do not have a time machine to go back and change products that we
>> already shipped to the customers. It is probably the same story as with
>> Hyper-V's vmbus which is not virtio.
>>
>> Besides, virtio is not available on non-Linux guests with we have to
>> support as well, and than affected the design decisions in hypervisor
>> layer that have been made several years ago.

Indeed there is no time machine and I definitely agree you won't be able 
to port VMCI to virtio-serial w/o major breakage for existing users.

Nevertheless, as I wrote on my previous feedback [1], you can make the 
VMCI socket generic in a way that virtio-serial users would be able to 
enjoy. This way VMW users will get out of the box experience w/o any 
change while KVM users will get socket abstraction layer which carry 
some benefit over the virtio-serial ports.

Dor

[1] https://lkml.org/lkml/2012/5/16/126

>
> Ok, thanks for clearing that up, I was confused here.
>
> greg k-h
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