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Tsirkin" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Cc: Filip Hejsek , qemu-devel@nongnu.org, =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , Paolo Bonzini , Laurent Vivier , Amit Shah , Markus Armbruster , Eric Blake , Eduardo Habkost , Marcel Apfelbaum , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Yanan Wang , Zhao Liu , Szymon Lukasz , Maximilian Immanuel Brandtner Subject: Re: [PATCH v4 00/10] virtio-console: notify about the terminal size Message-ID: <20250912045228-mutt-send-email-mst@kernel.org> References: <20250912-console-resize-v4-0-7925e444afc4@gmail.com> <20250912042910-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Sep 12, 2025 at 09:50:30AM +0100, Daniel P. Berrangé wrote: > On Fri, Sep 12, 2025 at 04:41:02AM -0400, Michael S. Tsirkin wrote: > > On Fri, Sep 12, 2025 at 05:39:45AM +0200, Filip Hejsek wrote: > > > The goal of this series is to have a resizable terminal into a guest > > > without having to set up networking and using, e.g. ssh. > > > > > > The virtio spec allows a virtio-console device to notify the guest about > > > terminal resizes in the host. Linux Kernel implements the driver part of > > > the spec. This series implement the device part in QEMU. > > > > > > This series adds support for a resizable terminal if a virtio console > > > device is connected to the stdio backend. > > > > > > This series also introduces resize messages that can be sent over QMP to > > > notify QEMU about the size of the terminal connented to some chardev. > > > In the libvirt setting, it will allow to implement a resizable terminal > > > for virsh console and other libvirt clients. > > > > > > This patch series was originally authored by Szymon Lukasz and submitted > > > to qemu-devel about 5 years ago. The previous submission can be found at > > > . > > > I have updated the patches to be compatible with latest master and made > > > a few small changes of my own, including the addition of Windows support. > > > > > > Probably the most important change I made is the swapping of rows and > > > cols fields in resize messages. I would like to hear some feedback on > > > this change from reviewers. The problem is that for a long time, the > > > Linux kernel used a different field order from what was specified in the > > > virtio spec. The kernel implementation was apparently merged around 2010, > > > while the virtio spec came in 2014, so when a previous version of this > > > patch series was being discussed here on this mailing list in 2020, it > > > was decided that QEMU should match the Linux implementation, and ideally, > > > the virtio spec should be changed. > > > > > > However, recently, the Linux kernel implementation was changed to conform > > > to the spec: . > > > As a result, to be compatible with latest kernel releases, QEMU needs to > > > also use the field order matching the specification. I have changed the > > > patch to use the spec-compliant order, so it works correctly with latest > > > kernels now. > > > > > > > Well this is not in any release yet. If you want me to revert that > > one, let me know ASAP. Maximilian? > > > > > That leaves the issue of older kernels. There are about 15 years' worth > > > of kernel versions with the swapped field order, including the kernel > > > currently shipped in Debian stable. The effects of the swapped dimensions > > > can sometimes be quite annoying - e.g. if you have a terminal with > > > 24 rows, this will be interpreted as 24 columns, and your shell may limit > > > line editing to this small space, most of which will be taken by your > > > prompt. The patch series in its current form provides no way to disable > > > the console size functionality, > > > > Well I see the console-size property, no? > > At least in the case of libvirt managed VMs, this series does > nothin by default, as they won't be using the 'stdio' chardev, > they'll require libvirt to first wire up the new QMP command, > and then apps using libvirt to call it. So in that sense, it'll > take a while before the effects are seen by users. > > > > so users may end up worse off than if > > > the functionality were not implemented at all. > > > > If we want to keep the Linux patch, the straight forward way is to send > > the fix to stable@ then poke at Debian at al to fix their kernels. > > > > Another option is to make the property default to off, have > > management turn it on when guest is up to date. > > > > But it really sounds like we should revert that Linux patch. > > I posted a revert, pls comment. > > What about other non-Linux guest OS that may have correctly > implemented the virtio spec ? > > At least FreeBSD appears to /not/ implemenmt resize at all: > > https://github.com/freebsd/freebsd-src/blob/main/sys/dev/virtio/console/virtio_console.c#L884 > > Do we have a Windows impl of virtio-console with resize support ? Windows seems to ignore it: case VIRTIO_CONSOLE_RESIZE: TraceEvents(TRACE_LEVEL_INFORMATION, DBG_PNP, "VIRTIO_CONSOLE_RESIZE id = %d\n", cpkt->id); break; > Any other places we should check ? > > With 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 :|