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

[Justinien Bouron]

Depending on your use-case, it might be inconvenient to have qemu grab
the input device immediately upon starting the guest, especially if the
guest takes a while to start in which case it may take a few seconds
before being able to release the device via the toggle combination.

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, ie. same
behaviour as before this change.

Signed-off-by: Justinien Bouron <justinien.bouron@gmail.com>
---
 qapi/qom.json    | 13 ++++++++++++-
 ui/input-linux.c | 20 +++++++++++++++++++-
 2 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/qapi/qom.json b/qapi/qom.json
index 032c6fa037..50e66d55cc 100644
--- a/qapi/qom.json
+++ b/qapi/qom.json
@@ -508,13 +508,24 @@
 # @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, ie. 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: 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..cf9376ddb0 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);
     }
     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 = {
-- 
2.43.0