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

From: Jamie Lokier
Subject: Re: [Qemu-devel] Re: virtio-serial: An interface for host-guest communication
Date: Thu, 20 Aug 2009 18:10:18 +0100
User-agent: Mutt/1.5.13 (2006-08-11)

Amit Shah wrote:
> > 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.

How would a third party go about assigning themselves a number?

For the sake of example, imagine they develop a simple service like
"guesttop" which let's the host get a listing of guest processes.

They'll have to distributed app-specific udev rule patches for every
guest distro, which sounds like a lot of work.  The app itself is
probably a very simple C program; the hardest part of making it
portable across distros would be the udev rules, which is silly.

Anyway, every other device has a name or uuid these days.  You can
still use /dev/sda1 to refer to your boot partition, but LABEL=boot is
also available if you prefer.  Isn't that the ethos these days?

Why not both?  /dev/vmch05 if you prefer, plus symlink
/dev/vmch-guesttop -> /dev/vmch05 if name=guesttop was given to QEMU.

If you do stay with numbers only, note that it's not like TCP/UDP port
numbers because the number space is far smaller.  Picking a random
number that you hope nobody else uses is harder.

... Back to technical bits.  If config space is tight, use a channel!
Dedicate channel 0 to control, used to fetch the name (if there is
one) for each number.

-- Jamie

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