On Wed, 2025-03-05 at 13:15 +0100, Niklas Schnelle wrote: > On Wed, 2025-03-05 at 13:13 +0100, Niklas Schnelle wrote: > > On Wed, 2025-03-05 at 10:53 +0100, Maximilian Immanuel Brandtner > > wrote: > > > On Mon, 2025-03-03 at 12:54 +0100, Amit Shah wrote: > > > > On Tue, 2025-02-25 at 10:21 +0100, Maximilian Immanuel > > > > Brandtner > > > > wrote: > > > > > According to the virtio spec[0] the virtio console resize > > > > > struct > > > > > defines > > > > > cols before rows. In the kernel implementation it is the > > > > > other way > > > > > around > > > > > resulting in the two properties being switched. > > > > > > > > Not true, see below. > > > > > > > > > While QEMU doesn't currently support resizing consoles, > > > > > TinyEMU > > > > > > > > QEMU does support console resizing - just that it uses the > > > > classical > > > > way of doing it: via the config space, and not via a control > > > > message > > > > (yet). > > > > > > > > https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/virtio_console.c#n1787 > > > > > > > > https://lists.nongnu.org/archive/html/qemu-devel/2010-05/msg00031.html > > > > > > I didn't know about this patch-set, however as of right now QEMU > > > does > > > not set VIRTIO_CONSOLE_F_SIZE, never uses VIRTIO_CONSOLE_RESIZE, > > > and > > > resizing is never mentioned in hw/char/virtio-console.c or > > > hw/char/virtio-serial-bus.c. Suffice to say I don't see any > > > indicating > > > of resize currently being used under QEMU. Perhaps QEMU supported > > > resizing at one point, but not anymore. If you disagree please > > > send me > > > where the resizing logic can currently be found in the QEMU > > > source > > > code. I at least was unable to find it. > > > > > > > > > > > > diff --git a/drivers/char/virtio_console.c > > > > > b/drivers/char/virtio_console.c > > > > > index 24442485e73e..9668e89873cf 100644 > > > > > --- a/drivers/char/virtio_console.c > > > > > +++ b/drivers/char/virtio_console.c > > > > > @@ -1579,8 +1579,8 @@ static void > > > > > handle_control_message(struct > > > > > virtio_device *vdev, > > > > > break; > > > > > case VIRTIO_CONSOLE_RESIZE: { > > > > > struct { > > > > > - __u16 rows; > > > > > __u16 cols; > > > > > + __u16 rows; > > > > > } size; > > > > > > > > > > if (!is_console_port(port)) > > > > > > > > This VIRTIO_CONSOLE_RESIZE message is a control message, as > > > > opposed > > > > to > > > > the config space row/col values that is documented in the spec. > > > > > > > > Maybe more context will be helpful: > > > > > > > > Initially, virtio_console was just a way to create one hvc > > > > console > > > > port > > > > over the virtio transport. The size of that console port could > > > > be > > > > changed by changing the size parameters in the virtio device's > > > > configuration space. Those are the values documented in the > > > > spec. > > > > These are read via virtio_cread(), and do not have a struct > > > > representation. > > > > > > > > When the MULTIPORT feature was added to the virtio_console.c > > > > driver, > > > > more than one console port could be associated with the single > > > > device. > > > > Eg. we could have hvc0, hvc1, hvc2 all as part of the same > > > > device. > > > > With this, the single config space value for row/col could not > > > > be > > > > used > > > > for the "extra" hvc1/hvc2 devices -- so a new > > > > VIRTIO_CONSOLE_RESIZE > > > > control message was added that conveys each console's > > > > dimensions. > > > > > > > > Your patch is trying to change the control message, and not the > > > > config > > > > space. > > > > > > > > Now - the lack of the 'struct size' definition for the control > > > > message > > > > in the spec is unfortunate, but that can be easily added -- and > > > > I > > > > prefer we add it based on this Linux implementation (ie. first > > > > rows, > > > > then cols). > > > > > > > > But note that all this only affects devices that implement > > > > multiport > > > > support, and have multiple console ports on a single device. I > > > > don't > > > > recall there are any implementations using such a > > > > configuration. > > > > > > > > ... which all leads me to ask if you've actually seen a > > > > misconfiguration happen when trying to resize consoles which > > > > led to > > > > this patch. > > > > > > > > Amit > > > > > > I'm working on implementing console resizing for virtio in QEMU > > > and > > > Libvirt. As SIGWINCH is raised on the virsh frontend the new > > > console > > > size needs to be transfered to QEMU (in my RFC patch via QOM, > > > which > > > then causes QEMU to trigger a virtio control msg in the > > > chr_resize > > > function of the virtio-console chardev). (The patch-set should > > > make its > > > way unto the QEMU mailing-list soon). The way I implemented it > > > QEMU > > > sends a resize control message where the control message has the > > > following format: > > > > > > ``` > > > struct { > > > le32 id; // port->id > > > le16 event; // VIRTIO_CONSOLE_RESIZE > > > le16 value; // 0 > > > le16 cols; // ws.ws_col > > > le16 rows; // ws.ws_row > > > } > > > ``` > > > > > > This strongly seems to me to be in accordance with the spec[0]. > > > It > > > resulted in the rows and cols being switched after a resize > > > event. I > > > was able to track the issue down to this part of the kernel. > > > Applying > > > the patch I sent upstream, fixed the issue. > > > As of right now I only implemented resize for multiport (because > > > in the > > > virtio spec I was only able to find references to resizing as a > > > control > > > message which requires multiport. In your email you claimed that > > > config > > > space resizing exists as well. I was only able to find references > > > to > > > resizing as a control message in the spec. I would love to see > > > what > > > part of the spec you are refering to specifically, as it would > > > allow me > > > to implement resizing without multiport as well). > > > It seems to me that either the spec or the kernel implementation > > > has to > > > change. If you prefer changing the spec that would be fine by me > > > as > > > well, however there seems to be no implementation that uses the > > > linux > > > ordering and Alpine seems to patch their kernel to use the spec > > > ordering instead (as described in the initial email)(this was > > > really > > > Niklas Schnelle's finding so for further questions I would refer > > > to > > > him). > > > > I don't think this was patched in the (official) alpine kernel. > > What > > happened is that I tested TinyEMU[0] with the kernel + initrd from > > the > > JSLinux site and that has working console resizing. In the TinyEMU > > code > > this is implemented in > > TinyEMU/virtio.c:virtio_console_resize_event(): > > > > void virtio_console_resize_event(VIRTIODevice *s, int width, int > > height) > > { > > /* indicate the console size */ > > put_le16(s->config_space + 0, width); > > put_le16(s->config_space + 2, height); > > > > virtio_config_change_notify(s); > > } > > > > On second look this indeed seems to use the config space. It writes > > first the width then height which matches config_work_handler(). > > But > > like Maximilian I could only find the VIRTIO_CONSOLE_RESIZE message > > mechanism in the spec, also with width (cols) then height (rows) > > but > > not matching the kernel struct changed by this patch. > > > > Forgot to note, the idea that Alpine was patched came because the > kernel used in TinyEMU has '-dirty' in the local version so we were > wondering if it was patched for this. But seeing the > config_work_handler() it's probably just using that. > > Thanks, > Niklas In that case it might be better to change the spec to reflect the kernel implementation of resize control messages. Max
