Re: [PATCH] virtio_console: Add support for multiple ports for genericguest and host communication

[Anthony Liguori]

Amit Shah wrote:
> On (Tue) Sep 15 2009 [07:57:10], Anthony Liguori wrote:
>   
> > Amit Shah wrote:
> >     
> > > Hey Greg,
> > >
> > > Can you tell me how this could work out -- each console port could have
> > > a "role" string associated with it (obtainable from the invoking qemu
> > > process in case of qemu/kvm). Something that I have in mind currently
> > > is:
> > >
> > > $ qemu-kvm ... -virtioconsole role=org/qemu/clipboard
> > >
> > > and then the guest kernel sees the string, and puts the
> > > "org/qemu/clipboard" in some file in sysfs. Guest userspace should then
> > > be able to open and read/write to
> > >
> > > /dev/virtio_console/org/qemu/clipboard
> > >   
> > >       
> > That's probably not what we want.  I imagine what we want is:
> >
> > /dev/ttyV0
> > /dev/ttyV1
> > /dev/ttyVN
> >
> > And then we want:
> >
> > /sys/class/virtio-console/ttyV0/name -> "org.qemu.clipboard"
> >
> > Userspace can detect when new virtio-consoles appear via udev events.   
> > When it sees a new ttyVN, it can then look in sysfs to discover it's 
> > name.
> >     
>
> OK; but that's kind of roundabout isn't it? An application, instead of
> watching for the console port it's interested in, has to instead monitor
> all the ports.
>   

If you wanted to use /dev/virtio/org/qemu/clipboard you still have the 
same problem.  You have to use udev or inotify to listen for a new file 
in a directory.

The /dev/ path may look nicer from a high level, but the code ends up 
being roughly the same for either approach.  What I propose has the 
advantage of looking like existing subsystems.  It also avoids encoding 
device information in the device name.

> So in effect there has to be one app monitoring for new ports and then
> that app exec'ing the corresponding app meant for that port.
>   

I think if you think through both models, they end up looking the same.

Regards,

Anthony Liguroi
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