Re: [PATCH v2 0/6] virtio-console: notify about the terminal size

[Szymon Lukasz <noh4hss@gmail.com>]

On Wed, Jun 24, 2020 at 12:49:15PM +0100, Daniel P. Berrangé wrote:
> On Wed, Jun 24, 2020 at 01:26:34PM +0200, Szymon Lukasz wrote:
> > Also there is a problem with the virtio spec and Linux Kernel
> > implementation, the order of fields in virtio_console_resize struct
> > differs between the kernel and the spec. I do not know if there is any
> > implementation of the virtio-console driver that handles resize messages
> > and uses a different order than Linux.
> 
> Well this is a bit of a mess :-(
> 
> The main virtio_console_config struct has cols, then rows.
> 
> The Linux impl of resizing appears to have arrived in 2010, and created
> a new struct with rows, then cols.
> 
> commit 8345adbf96fc1bde7d9846aadbe5af9b2ae90882
> Author: Amit Shah <amit.shah@redhat.com>
> Date:   Thu May 6 02:05:09 2010 +0530
> 
>     virtio: console: Accept console size along with resize control message
>     
>     The VIRTIO_CONSOLE_RESIZE control message sent to us by the host now
>     contains the new {rows, cols} values for the console. This ensures each
>     console port gets its own size, and we don't depend on the config-space
>     rows and cols values at all now.
>     
>     Signed-off-by: Amit Shah <amit.shah@redhat.com>
>     CC: Christian Borntraeger <borntraeger@de.ibm.com>
>     CC: linuxppc-dev@ozlabs.org
>     CC: Kusanagi Kouichi <slash@ac.auone-net.jp>
>     Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
> 
> 
> The virtio spec documenting this came 4 years later in 2014 and documented
> the resize struct with cols, then rows, which differs from Linux impl,
> but matches ordering of the main virtio_console_config:
> 
> commit 908cfaa782e950d6656d947599d7a6c9fb16cad1
> Author: rusty <rusty@0c8fb4dd-22a2-4bb5-bc14-6c75a5f43652>
> Date:   Wed Feb 12 03:15:57 2014 +0000
> 
>     Feedback #6: Applied
>     
>     As per minutes:
>             https://lists.oasis-open.org/archives/virtio/201402/msg00121.html
>     
>     Signed-off-by: Rusty Russell <rusty@au1.ibm.com>
>     
>     git-svn-id: https://tools.oasis-open.org/version-control/svn/virtio@237 0c8fb4dd-22a2-4bb5-bc14-6c75a5f43652
> 
> I can understand why it is desirable for the resize struct to match
> the order of the initial config struct.  I'm guessing it just wasn't
> realized that the Linux impl was inverted for resize
> 
> The FreeBSD impl of virtio-console doesn't do resize:
> 
>   https://github.com/freebsd/freebsd/blob/master/sys/dev/virtio/console/virtio_console.c#L874
> 
> Not sure what other impls are going to be around, but I feel like
> Linux is going to be the most commonly deployed by orders of magnitude.
> 
> So I'd say QEMU should match Linux, and the spec should be fixed.

I had the same thoughts. I will ask for a change in the spec.
> 
> 
> Have you reported this bug to the virtio spec people directly yet ?
> 
> I don't see an issue open at
> 
>   https://github.com/oasis-tcs/virtio-spec/issues/
> 
> so I think one should be filed there
> 
> Regards,
> Daniel
> -- 
> |: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
> |: https://libvirt.org         -o-            https://fstop138.berrange.com :|
> |: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|
>