Re: [Qemu-devel] Re: virtio-serial: An interface for host-guest communication

[Amit Shah]

On (Mon) Jul 27 2009 [18:44:28], Anthony Liguori wrote:
> Jamie Lokier wrote:
>> With multiple X servers, there can be more than one currently logged in user.
>>
>> Same with multiple text consoles - that's more familiar.
>>
>> Which one owns /dev/vmch3?
>>   
>
> For a VMM, copy/paste should work with whatever user has the active X  
> session that's controlling the physical display.
>
> Yes, it could get complicated if we supported multiple video cards, but  
> fortunately we don't :-)
>
> I really think you need to have a copy/paste daemon that allows multiple  
> X sessions to connect to it and then that daemon can somehow determine  
> who is the "active" session.
>
> This is part of the reason I've been pushing for a concrete example.   
> All the signs here point to a privileged daemon that delegates to  
> multiple users.  I think just about any use-case will have a similar 
> model.
>
> It really suggests that you need _one_ vmchannel that's exposed to  
> userspace with a single userspace daemon that consumes it.  You want the  
> flexibility of a userspace daemon in determining how you multiplex and  
> do security.  I don't think it's something you want to bake into the  
> userspace/kernel interface.

Right; use virtio just as the transport and all the interesting
activity happens in userspaces. That was the basis with which I started.
I can imagine dbus doing the copy/paste, lock screen, etc. actions.

However for libguestfs, dbus isn't an option and they already have some
predefined agents for each port. So libguestfs is an example for a
multi-port usecase for virtio-serial.

> And if you have a single daemon that serves vmchannel sessions, that  
> daemon can make it transparent whether the session is going over  
> /dev/ttyS0, a network device, /dev/hvc1, etc.

or /dev/vmch0. it doesn't matter. All minimal virtio devices will look
the same. Pop buffers, populate them, push them, etc.

                Amit