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

[Amit Shah]

On (Thu) Aug 20 2009 [09:44:29], Gerd Hoffmann wrote:
> On 08/20/09 09:31, Rusty Russell wrote:
>> On Sat, 15 Aug 2009 01:55:32 am Anthony Liguori wrote:
>>> Gerd Hoffmann wrote:
>>>> Also I still think passing a 'protocol' string for each port is a good
>>>> idea, so you can stick that into a sysfs file for guests use.
>>> Or drops ports altogether and just use protocol strings...
>>
>> Both is silly, yes.
>>
>> I guess strings + HAL magic can make the /dev names sane.  I don't want to
>> see userspace trolling through sysfs to figure out what device to open.
>
> udev can create sane /dev names (or symlinks) by checking sysfs  
> attributes, apps just open the /dev/whatever then.

There still will have to be some way in transferring all the strings
from qemu to the guest. Could be done from the config space, but will
have to be done one port at a time (config space is limited in size).

>> Which is why I prefer assigned numbers, which get mapped to minors.
>
> ports map trivially to minors.  When using protocol strings minors can  
> simply be dynamically auto-allocated by the guest and we don't need the  
> port numbers in the host<->guest protocol any more.
>
> I think strings are better as numbers for identifying protocols as you  
> can work without a central registry for the numbers then.

I like the way assigned numbers work: it's simpler to code, needs a
bitmap for all the ports that fits in nicely in the config space and
udev rules / scripts can point /dev/vmch02 to /dev/console.

                Amit