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From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Maximilian Immanuel Brandtner <maxbr@linux.ibm.com>
Cc: Filip Hejsek <filip.hejsek@gmail.com>,
	amit@kernel.org, armbru@redhat.com, eblake@redhat.com,
	eduardo@habkost.net, lvivier@redhat.com,
	marcandre.lureau@redhat.com, marcel.apfelbaum@gmail.com,
	mst@redhat.com, noh4hss@gmail.com, pbonzini@redhat.com,
	philmd@linaro.org, qemu-devel@nongnu.org, wangyanan55@huawei.com,
	zhao1.liu@intel.com, nsg@linux.ibm.com
Subject: Re: [PATCH v2] char-pty: add support for the terminal size
Date: Thu, 18 Sep 2025 09:48:09 +0100	[thread overview]
Message-ID: <aMvHScAtr3E_H2KB@redhat.com> (raw)
In-Reply-To: <8979fb7f27b9dbe48f6419d515c4d33a77cefe0a.camel@linux.ibm.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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  reply	other threads:[~2025-09-18  8:49 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-09-12  3:39 [PATCH v4 00/10] virtio-console: notify about the terminal size Filip Hejsek
2025-09-12  3:39 ` [PATCH v4 01/10] chardev: add cols, rows fields Filip Hejsek
2025-09-12  3:39 ` [PATCH v4 02/10] chardev: add CHR_EVENT_RESIZE Filip Hejsek
2025-09-12  3:39 ` [PATCH v4 03/10] chardev: add qemu_chr_resize() Filip Hejsek
2025-09-18  8:45   ` Maximilian Immanuel Brandtner
2025-09-18  9:31     ` Filip Hejsek
2025-09-12  3:39 ` [PATCH v4 04/10] char-mux: add support for the terminal size Filip Hejsek
2025-09-18  8:32   ` Maximilian Immanuel Brandtner
2025-09-18  9:11     ` Filip Hejsek
2025-09-12  3:39 ` [PATCH v4 05/10] main-loop: change the handling of SIGWINCH Filip Hejsek
2025-09-12  3:39 ` [PATCH v4 06/10] char-stdio: add support for the terminal size Filip Hejsek
2025-09-12  3:39 ` [PATCH v4 07/10] qmp: add chardev-resize command Filip Hejsek
2025-09-12 14:01   ` Markus Armbruster
2025-09-12 18:10     ` Filip Hejsek
2025-09-15  6:35       ` Markus Armbruster
2025-09-15 22:22         ` Filip Hejsek
2025-09-16 13:07           ` Markus Armbruster
2025-09-16 17:01             ` Filip Hejsek
2025-09-17  8:25               ` Markus Armbruster
2025-09-12  3:39 ` [PATCH v4 08/10] virtio-serial-bus: add terminal resize messages Filip Hejsek
2025-09-12 13:50   ` Markus Armbruster
2025-09-12 15:02     ` Filip Hejsek
2025-09-18  8:23   ` Daniel P. Berrangé
2025-09-18  8:51     ` Filip Hejsek
2025-09-12  3:39 ` [PATCH v4 09/10] virtio-console: notify the guest about terminal resizes Filip Hejsek
2025-09-12  3:39 ` [PATCH v4 10/10] char-win-stdio: add support for terminal size Filip Hejsek
2025-09-12  8:41 ` [PATCH v4 00/10] virtio-console: notify about the " Michael S. Tsirkin
2025-09-12  8:44   ` Michael S. Tsirkin
2025-09-12  8:50   ` Daniel P. Berrangé
2025-09-12  8:54     ` Michael S. Tsirkin
2025-09-15  8:41     ` Maximilian Immanuel Brandtner
2025-09-15  8:44       ` Daniel P. Berrangé
2025-09-15 16:25         ` [PATCH] char-pty: add support for " Maximilian Immanuel Brandtner
2025-09-15 16:34           ` [PATCH v2] " Maximilian Immanuel Brandtner
2025-09-15 16:36             ` Michael S. Tsirkin
2025-09-15 22:02             ` Filip Hejsek
2025-09-17  9:39               ` Maximilian Immanuel Brandtner
2025-09-17 13:09                 ` Filip Hejsek
2025-09-17 13:31                   ` Daniel P. Berrangé
2025-09-17 14:08                     ` Filip Hejsek
2025-09-17 16:17                       ` Daniel P. Berrangé
2025-09-17 17:11                         ` Filip Hejsek
2025-09-17 17:53                           ` Daniel P. Berrangé
2025-09-17 18:29                             ` Filip Hejsek
2025-09-18  8:35                               ` Daniel P. Berrangé
2025-09-18  8:39                                 ` Maximilian Immanuel Brandtner
2025-09-18  8:48                                   ` Daniel P. Berrangé [this message]
2025-09-18  8:54                                     ` Maximilian Immanuel Brandtner
2025-09-18  8:59                                       ` Daniel P. Berrangé
2025-09-18  9:05                                         ` Maximilian Immanuel Brandtner
2025-09-18 19:21                                           ` Filip Hejsek
2025-09-18  7:53                     ` Maximilian Immanuel Brandtner
2025-09-18  8:10                       ` Filip Hejsek
2025-09-12 14:24   ` [PATCH v4 00/10] virtio-console: notify about " Filip Hejsek
2025-09-15 23:02 ` Filip Hejsek
2025-09-15 23:08   ` Michael S. Tsirkin
2025-09-17 18:32     ` Filip Hejsek

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