Re: [PATCH v2] char-pty: add support for the terminal size

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Sep 18, 2025 at 10:39:28AM +0200, Maximilian Immanuel Brandtner wrote:
> On Thu, 2025-09-18 at 09:35 +0100, Daniel P. Berrangé wrote:
> > On Wed, Sep 17, 2025 at 08:29:39PM +0200, Filip Hejsek wrote:
> > > On Wed, 2025-09-17 at 18:53 +0100, Daniel P. Berrangé wrote:
> > > > On Wed, Sep 17, 2025 at 07:11:03PM +0200, Filip Hejsek wrote:
> > > > > On Wed, 2025-09-17 at 17:17 +0100, Daniel P. Berrangé wrote:
> > > > > 
> > > > > > We shouldn't send any size info to the guest if the hsot
> > > > > > backend
> > > > > > does not have it available.
> > > > > 
> > > > > Does that mean sending 0x0, or not sending anything at all? The
> > > > > later
> > > > > is tricky, because for non-multiport devices it's only really
> > > > > possible
> > > > > by not offering the feature bit, but we don't know upfront
> > > > > whether the
> > > > > size command will be used.
> > 
> > What are the semantics in the guest if we sent 0x0 as the size ?
> > AFAICT the virtio spec is silent on what '0x0' means.
> > 
> > It seems like it could conceivably have any behaviour, whether
> > a zero-size console, or a console clamped to 1x1 as a min size,
> > or a console reset to an arbitrary guest default like 80x24.
> 
> During testing the kernel resized the tty to 0x0 if VirtIO instructed
> the kernel to resize the tty to 0x0.

If the chardev backends are defaulting to 0x0 for everything except
the 'stdio' backend, then this series is surely going to break all
existing usage of virtio-console for non-stdio backends ?

What am I missing here ?

With regards,
Daniel
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