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.
> + 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]>
