Re: [Qemu-devel] [PATCH] virtio-input: send rel-wheel events for wheel buttons

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Aug 09, 2017 at 12:47:50AM +0200, Marc-André Lureau wrote:
> qemu uses wheel-up/down button events for mouse wheel input, however
> linux applications typically want REL_WHEEL events.
> 
> This fixes wheel with linux guests. Tested with X11/wayland, and
> windows virtio-input driver.
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  hw/input/virtio-input-hid.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/input/virtio-input-hid.c b/hw/input/virtio-input-hid.c
> index 46c038110c..f46857f0e4 100644
> --- a/hw/input/virtio-input-hid.c
> +++ b/hw/input/virtio-input-hid.c
> @@ -196,6 +196,7 @@ static void virtio_input_handle_event(DeviceState *dev, QemuConsole *src,
>      InputKeyEvent *key;
>      InputMoveEvent *move;
>      InputBtnEvent *btn;
> +    unsigned int map;
>  
>      switch (evt->type) {
>      case INPUT_EVENT_KIND_KEY:
> @@ -215,9 +216,15 @@ static void virtio_input_handle_event(DeviceState *dev, QemuConsole *src,
>          break;
>      case INPUT_EVENT_KIND_BTN:
>          btn = evt->u.btn.data;
> -        if (keymap_button[btn->button]) {
> +        map = keymap_button[btn->button];
> +        if (map == BTN_GEAR_DOWN || map == BTN_GEAR_UP) {
> +            event.type  = cpu_to_le16(EV_REL);
> +            event.code  = cpu_to_le16(REL_WHEEL);
> +            event.value = cpu_to_le32(map == BTN_GEAR_DOWN ? -1 : 1);

I realize now that value is actually a signed integer in 2's complement
format. Unfortunate that it's not documented.

> +            virtio_input_send(vinput, &event);
> +        } else if (map) {
>              event.type  = cpu_to_le16(EV_KEY);
> -            event.code  = cpu_to_le16(keymap_button[btn->button]);
> +            event.code  = cpu_to_le16(map);
>              event.value = cpu_to_le32(btn->down ? 1 : 0);
>              virtio_input_send(vinput, &event);
>          } else {
> @@ -424,9 +431,9 @@ static struct virtio_input_config virtio_mouse_config[] = {
>      },{
>          .select    = VIRTIO_INPUT_CFG_EV_BITS,
>          .subsel    = EV_REL,
> -        .size      = 1,
> +        .size      = 2,
>          .u.bitmap  = {
> -            (1 << REL_X) | (1 << REL_Y),
> +            (1 << REL_X) | (1 << REL_Y),  (1 << (REL_WHEEL - 8))

Works only when REL_WHEEL is between 8 and 15.
Add BUILD_BUG_ON?

>          },
>      },
>      { /* end of list */ },

Is it problematic e.g. if you migrate from a host with REL_WHEEL
to one without? Should we maintain a version without REL_WHEEL
for old machine types?


> -- 
> 2.14.0.1.geff633fa0