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

From: Amit Shah
Subject: Re: [Qemu-devel] Re: virtio-serial: An interface for host-guest communication
Date: Thu, 20 Aug 2009 19:12:41 +0530
User-agent: Mutt/1.5.19 (2009-01-05)

On (Fri) Aug 14 2009 [08:29:28], Anthony Liguori wrote:
> Amit Shah wrote:
>> On (Mon) Aug 10 2009 [11:59:31], Anthony Liguori wrote:
>>> However, as I've mentioned repeatedly, the reason I won't merge   
>>> virtio-serial is that it duplicates functionality with 
>>> virtio-console.   If the two are converged, I'm happy to merge it.  
>>> I'm not opposed to  having more functionality.
>> The guest code sort-of ends up looking like this after merging
>> virtio_console into virtio_serial. Diff is against virtio_serial in my
>> git tree, but that should be pretty close to the last submission I made
>> at
>> http://patchwork.kernel.org/patch/39335/
>> or the tree at
>> git://git.kernel.org/pub/scm/linux/kernel/git/amit/vs-kernel.git
>> I've merged bits from virtio_console.c into virtio_serial.c. If needed,
>> virtio_serial can be renamed to virtio_console. The VIRITIO_ID also
>> needs to change to that of virtio_console's.
>> Similar changes are needed for userspace.
>> Since there's support for only one console as of now, I've assigned port
>> #2 as the console port so that we hook into hvc when a port is found at
>> that location.
>> One issue that crops up for put_chars: a copy of the buffer to be sent
>> has to be made as we don't wait for host to ack the buffer before we
>> move on.
>> The biggest loss so far is Rusty's excellent comments: they will have to
>> be reworked and added for the whole of the new file.
>> Is this approach acceptable?
> I think we want to keep virtio_console.c and definitely continue using  
> the virtio_console id.

I've now seen some more code here and to me it looks like virtioconsole
is not used on any of the guests that qemu supports. The virtio_console
kernel module only works with lguest and s390 currently. There is one
feature and some config values supported by the kernel module but not in

So it looks as if we have virtio-console merged but no one uses it. Is
this right?

If that's the case, I'll send patches to replace virtio-console with
virtio-serial, making sure we keep the command line arg,

-virtioconsole <qemu char dev>

which will be translated to something like

-virtioserial <qemu char dev>,port=2


-virtioserial <qemu char dev>,protocol=console

depending on what we finalise on.

Does anyone have objections to this or pointers for me to see where
virtioconsole is actually used by qemu-supported guests?

I'm also open to convert the guest kernel virtio_console driver over
to support the new functionality, or just let that be and have a new
virtio-serial module.

Rusty, what's your take on this?


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