linux-kernel - Re: [PATCH v10 1/1] virtio_console: Add support for multiple ports for generic guest and host communication

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Message-ID: <4AF41DF0.7050002@us.ibm.com>
Date:	Fri, 06 Nov 2009 07:00:32 -0600
From:	Anthony Liguori <aliguori@...ibm.com>
To:	Christian Borntraeger <borntraeger@...ibm.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Amit Shah <amit.shah@...hat.com>, linux-kernel@...r.kernel.org,
	virtualization@...ux-foundation.org,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v10 1/1] virtio_console: Add support for multiple ports
 for generic guest and host communication

Christian Borntraeger wrote:
> I know that Anthony disagrees, but _If we start over_, I still think we should 
> use that chance and leave the old virtio console untouched and add a new driver 
> for the host guest communication. IMHO it turned out that there is only a tiny 
> bit of commonality. (most code pathes check for use_multiport and  then do two 
> completely different things).
> I like simplicity. According to David A. Wheeler's SLOCCount, the old console 
> has 141 lines of code and the I truly believe that a separate guest-host comm 
> vehicle would also be a lot simpler if it must not take care of the old 
> virtio_console interface.
>   

It's the wrong metrics for evaluating a device ABI.  We should consider 
device ABIs based on whether they make sense--not about how many lines 
of code it takes to implement the Linux driver.

Fundamentally speaking, right now, virtio-console is a single stream 
that acts as an interactive terminal.  What we're looking to add here is 
to support multiple terminals that can be enumerated in a rationale way.

I see no reason why that should be two separate devices.

> On the other hand we all should agree on one driver vs. two drivers before we go 
> on. Everything else would be unfair to Amit, who had the unpleasant task to 
> implement conflicting review comments....
>   

I agree and there are multiple maintainers on the qemu side who feel the 
same way I do.  I'm really strongly opposed to making this separate devices.

If you think it's easier, you can do a check in the virtio_probe 
function that checks for the feature bits and calls a completely 
separate virtio initialization routine so it ends up being two separate 
files in Linux.  But that's a Linux implementation detail.

> Christian
>   

-- 
Regards,

Anthony Liguori

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