On Wed, 2026-06-10 at 03:04 -0400, Michael S. Tsirkin wrote:
> On Mon, Feb 23, 2026 at 06:37:02PM +0100, Filip Hejsek wrote:
> > Previously, the size was only read upon receiving the config interrupt.
> > This interrupt is sent when the size changes. However, we also need to
> > read the initial size.
> >
> > Also make sure to only read the size from config if F_SIZE is enabled.
> >
> > Fixes: 9778829cffd4 ("virtio: console: Store each console's size in the
> > console structure")
> > Signed-off-by: Filip Hejsek <[email protected]>
> > ---
> > This is a resend of [1], which hasn't received any response.
> >
> > I found this bug while developing patches for QEMU that add virtio
> > console resize support. If you want to test this, you can get my QEMU
> > patches from [2]. You will need to disable multiport
> > using `-device virtio-serial,max_ports=1`.
> >
> > [1]:
> > https://lore.kernel.org/all/[email protected]/
> > [2]:
> > https://lore.kernel.org/all/[email protected]/
> >
> > I'll also repeat my questions from the previous submission here. These are
> > things that confused me when I was trying to understand the surrounding
> > code,
> > but should in no way prevent merging this patch.
> >
> > - Why does use_multiport use __virtio_test_bit instead of
> > virtio_has_feature?
> >
> > - The VIRTIO_CONSOLE_RESIZE handler sets irq_requested to 1, which I
> > think makes no sense?
> > ---
> > drivers/char/virtio_console.c | 52
> > ++++++++++++++++++++++++++-----------------
> > 1 file changed, 31 insertions(+), 21 deletions(-)
> >
> > diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> > index 088182e54d..c355f6d392 100644
> > --- a/drivers/char/virtio_console.c
> > +++ b/drivers/char/virtio_console.c
> > @@ -1771,32 +1771,40 @@ static void config_intr(struct virtio_device *vdev)
> > schedule_work(&portdev->config_work);
> > }
> >
> > -static void config_work_handler(struct work_struct *work)
> > +static void update_size_from_config(struct ports_device *portdev)
> > {
> > - struct ports_device *portdev;
> > + struct virtio_device *vdev;
> > + struct port *port;
> > + u16 rows, cols;
> >
> > - portdev = container_of(work, struct ports_device, config_work);
> > - if (!use_multiport(portdev)) {
> > - struct virtio_device *vdev;
> > - struct port *port;
> > - u16 rows, cols;
> > + vdev = portdev->vdev;
> >
> > - vdev = portdev->vdev;
> > - virtio_cread(vdev, struct virtio_console_config, cols, &cols);
> > - virtio_cread(vdev, struct virtio_console_config, rows, &rows);
> > + /*
> > + * We'll use this way of resizing only for legacy support.
> > + * For multiport devices, use control messages to indicate
> > + * console size changes so that it can be done per-port.
> > + *
> > + * Don't test F_SIZE at all if we're rproc: not a valid feature.
> > + */
> > + if (is_rproc_serial(vdev) ||
>
> Wait a second. Why is there this rproc test here?
> Was not in the original code and commit log says nothing about it.
>
Previously, this code was in config_work_handler(), which was never
called for rproc_serial (it's scheduled from config_intr(), which is
the config_changed handler only for virtio_console).
Now update_size_from_config() is called unconditionally from
virtcons_probe(), so it will be called for rproc_serial too, which
doesn't have the F_SIZE feature.
>
> > + use_multiport(portdev) ||
> > + !virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE))
> > + return;
> >
> > - port = find_port_by_id(portdev, 0);
> > - set_console_size(port, rows, cols);
> > + virtio_cread(vdev, struct virtio_console_config, cols, &cols);
> > + virtio_cread(vdev, struct virtio_console_config, rows, &rows);
> >
> > - /*
> > - * We'll use this way of resizing only for legacy
> > - * support. For newer userspace
> > - * (VIRTIO_CONSOLE_F_MULTPORT+), use control messages
> > - * to indicate console size changes so that it can be
> > - * done per-port.
> > - */
> > - resize_console(port);
> > - }
> > + port = find_port_by_id(portdev, 0);
> > + set_console_size(port, rows, cols);
> > + resize_console(port);
> > +}
> > +
> > +static void config_work_handler(struct work_struct *work)
> > +{
> > + struct ports_device *portdev;
> > +
> > + portdev = container_of(work, struct ports_device, config_work);
> > + update_size_from_config(portdev);
> > }
> >
> > static int init_vqs(struct ports_device *portdev)
> > @@ -2054,6 +2062,8 @@ static int virtcons_probe(struct virtio_device *vdev)
> > __send_control_msg(portdev, VIRTIO_CONSOLE_BAD_ID,
> > VIRTIO_CONSOLE_DEVICE_READY, 1);
> >
> > + update_size_from_config(portdev);
> > +
> > return 0;
> >
> > free_chrdev:
> >
> > ---
> > base-commit: b927546677c876e26eba308550207c2ddf812a43
> > change-id: 20251224-virtio-console-fix-3d46980ef569
> >
> > Best regards,
> > --
> > Filip Hejsek <[email protected]>
