[PATCH RFC xf86-input-libinput] Swap the registered input device on DEVICE_OFF when needed

[Peter Hutterer]

If we don't swap out the pInfo previously passed to xf86AddEnabledDevice(),
the thread eventually calls read_input on a struct that has been deleted.
Avoid this by swapping out the to-be-destroyed pInfo with the first one we
find.

FIXME: incomplete, this doesn't do any driver checking.

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
---
Hans: I'm not a big fan of copying the fields into our custom InputInfoRec,
it makes the inner workings of xf86AddEnabledDevice() and the thread
effectively input driver ABI. This one is a slightly nicer (yet incomplete)
solution, what do you think?

 src/xf86libinput.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/src/xf86libinput.c b/src/xf86libinput.c
index 69f7ae3..dcd3018 100644
--- a/src/xf86libinput.c
+++ b/src/xf86libinput.c
@@ -87,6 +87,7 @@
 struct xf86libinput_driver {
 	struct libinput *libinput;
 	int device_enabled_count;
+	void *registered_InputInfoPtr;
 };
 
 static struct xf86libinput_driver driver_context;
@@ -583,6 +584,7 @@ xf86libinput_on(DeviceIntPtr dev)
 	if (driver_context.device_enabled_count == 0) {
 #if HAVE_THREADED_INPUT
 		xf86AddEnabledDevice(pInfo);
+		driver_context.registered_InputInfoPtr = pInfo;
 #else
 		/* Can't use xf86AddEnabledDevice on an epollfd */
 		AddEnabledDevice(pInfo->fd);
@@ -1138,6 +1140,28 @@ xf86libinput_destroy(DeviceIntPtr dev)
 	struct xf86libinput *driver_data = pInfo->private;
 	struct xf86libinput_device *shared_device = driver_data->shared_device;
 
+	/* If the device being destroyed is the one we used for
+	 * xf86AddEnabledDevice(), we need to swap it out for one that is
+	 * still live. xf86AddEnabledDevice() buffers some data and once the
+	 * deletes pInfo (when  DEVICE_OFF completes) the thread will keep
+	 * calling that struct's read_input because we never removed it.
+	 * Avoid this by removing ours and substituting one that's still
+	 * valid, the fd is the same anyway (libinput's epollfd).
+	 */
+	if (pInfo == driver_context.registered_InputInfoPtr &&
+	    driver_context.device_enabled_count > 0) {
+		InputInfoPtr next = xf86FirstLocalDevice();
+		while (next == pInfo)
+			next = pInfo->next;
+
+		input_lock();
+		xf86RemoveEnabledDevice(pInfo);
+		if (next) /* shouldn't ever be NULL anyway */
+			xf86AddEnabledDevice(next);
+		driver_context.registered_InputInfoPtr = next;
+		input_unlock();
+	}
+
 	xorg_list_del(&driver_data->shared_device_link);
 
 	if (driver_data->tablet_tool)
-- 
2.7.4