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Date: Thu, 08 Dec 2011 08:37:38 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] Insane virtio-serial semantics
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To: Markus Armbruster <armbru@redhat.com>
Cc: Blue Swirl <blauwirbel@gmail.com>, Michael Roth <mdroth@linux.vnet.ibm.com>, qemu-devel@nongnu.org, Zhi Yong Wu <zwu.kernel@gmail.com>, amit.shah@redhat.com, Cam Macdonell <cam@cs.ualberta.ca>, =?ISO-8859-1?Q?Llu=EDs_Vilanova?= <vilanova@ac.upc.edu>

On 12/08/2011 04:11 AM, Markus Armbruster wrote:
> Anthony Liguori<anthony@codemonkey.ws>  writes:
>> And yes, I can't help but think of Dave Millers comments long ago that
>> any PV transport is eventually going to reinvent TCP, poorly.
>
> No doubt then, no doubt now.  But if I remember correctly, we didn't
> create virtio-serial because we thought we could do better than TCP/IP.
> We thought we need a zero-config communication channel that doesn't
> interfere in any way with the guest's networking.  Since the network
> folks were unwilling to give us one ("use TCP already"), we looked for
> another bare metal thing to imitate, and chose serial lines.
>
> Now, comparing serial lines to TCP/IP makes no sense.  Different layers.

virtio-serial is not a serial line.  It attempts to have connection semantics 
(like a socket) which is what the fundamental problem is.

It probably makes sense to have a virtio-serial2 that is exposed to the guest as 
a tty device and stick strictly to serial semantics.

> Layering a real network protocol on top of serial line is possible; SLIP
> exists.  But as long as we insist on "don't interfere in any way with
> the guest's networking", we can't use TCP, and thus are doomed to
> reinvent it, poorly.

I think we just got too clever.

Regards,

Anthony Liguori