Re: [PATCH v3] input-linux: Add option to not grab a device upon guest startup

[Marc-André Lureau]

Hi

On Wed, Apr 3, 2024 at 9:51 AM Justinien Bouron
<justinien.bouron@gmail.com> wrote:
>
> Depending on your use-case, it might be inconvenient to have qemu grab
> the input device from the host immediately upon starting the guest.
>
> Added a new bool option to input-linux: grab-on-startup. If true, the
> device is grabbed as soon as the guest is started, otherwise it is not
> grabbed until the toggle combination is entered. To avoid breaking
> existing setups, the default value of grab-on-startup is true, i.e. same
> behaviour as before this change.
>
> Signed-off-by: Justinien Bouron <justinien.bouron@gmail.com>
> ---
>
> Changes since v2:
>     - Added missing (since 9.1) to the new option in qapi/qom.json
>
>  qapi/qom.json    | 14 +++++++++++++-
>  ui/input-linux.c | 20 +++++++++++++++++++-
>  2 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/qapi/qom.json b/qapi/qom.json
> index 85e6b4f84a..2067e41991 100644
> --- a/qapi/qom.json
> +++ b/qapi/qom.json
> @@ -508,13 +508,25 @@
>  # @grab-toggle: the key or key combination that toggles device grab
>  #     (default: ctrl-ctrl)
>  #
> +# @grab-on-startup: if true, grab the device immediately upon starting
> +#     the guest.  Otherwise, don't grab the device until the
> +#     combination is entered.  This does not influence other devices
> +#     even if grab_all is true, i.e. in the unlikely scenario where
> +#     device1 has grab_all=true + grab-on-startup=true and device2 has
> +#     grab-on-startup=false, only device1 is grabbed on startup, then,
> +#     once the grab combination is entered, grabbing is toggled off
> +#     for both devices (because device1 enforces the grab_all
> +#     property) until the combination is entered again at which point
> +#     both devices will be grabbed.  (default: true)  (since 9.1).
> +#
>  # Since: 2.6
>  ##
>  { 'struct': 'InputLinuxProperties',
>    'data': { 'evdev': 'str',
>              '*grab_all': 'bool',
>              '*repeat': 'bool',
> -            '*grab-toggle': 'GrabToggleKeys' } }
> +            '*grab-toggle': 'GrabToggleKeys',
> +            '*grab-on-startup': 'bool'} }
>
>  ##
>  # @EventLoopBaseProperties:
> diff --git a/ui/input-linux.c b/ui/input-linux.c
> index e572a2e905..68b5c6d485 100644
> --- a/ui/input-linux.c
> +++ b/ui/input-linux.c
> @@ -44,6 +44,7 @@ struct InputLinux {
>      bool        grab_request;
>      bool        grab_active;
>      bool        grab_all;
> +    bool        grab_on_startup;
>      bool        keydown[KEY_CNT];
>      int         keycount;
>      int         wheel;
> @@ -400,7 +401,7 @@ static void input_linux_complete(UserCreatable *uc, Error 
> **errp)
>      if (il->keycount) {
>          /* delay grab until all keys are released */
>          il->grab_request = true;
> -    } else {
> +    } else if (il->grab_on_startup) {
>          input_linux_toggle_grab(il);
>      }

The patch looks ok to me, but you don't handle the case where keys are
pressed at startup and the grab is delayed. You could add a if
(!il->grab_on_startup) goto skip_grab, probably instead.

>      QTAILQ_INSERT_TAIL(&inputs, il, next);
> @@ -491,6 +492,19 @@ static void input_linux_set_grab_toggle(Object *obj, int 
> value,
>      il->grab_toggle = value;
>  }
>
> +static bool input_linux_get_grab_on_startup(Object *obj, Error **errp)
> +{
> +    InputLinux *il = INPUT_LINUX(obj);
> +    return il->grab_on_startup;
> +}
> +
> +static void input_linux_set_grab_on_startup(Object *obj, bool value,
> +                                            Error **errp)
> +{
> +    InputLinux *il = INPUT_LINUX(obj);
> +    il->grab_on_startup = value;
> +}
> +
>  static void input_linux_instance_init(Object *obj)
>  {
>  }
> @@ -498,6 +512,7 @@ static void input_linux_instance_init(Object *obj)
>  static void input_linux_class_init(ObjectClass *oc, void *data)
>  {
>      UserCreatableClass *ucc = USER_CREATABLE_CLASS(oc);
> +    ObjectProperty *grab_on_startup_prop;
>
>      ucc->complete = input_linux_complete;
>
> @@ -514,6 +529,9 @@ static void input_linux_class_init(ObjectClass *oc, void 
> *data)
>                                     &GrabToggleKeys_lookup,
>                                     input_linux_get_grab_toggle,
>                                     input_linux_set_grab_toggle);
> +    grab_on_startup_prop = object_class_property_add_bool(oc, 
> "grab-on-startup",
> +        input_linux_get_grab_on_startup, input_linux_set_grab_on_startup);
> +    object_property_set_default_bool(grab_on_startup_prop, true);
>  }
>
>  static const TypeInfo input_linux_info = {
> --
> 2.44.0
>