evdev: get the current slot value from the absinfo struct or mtdev

If touches are already present on the device, absinfo has the currently
active touch slot. There's a race condition where the slot may change before
we enable the fd and we thus miss out on the ABS_MT_SLOT event. It's still
slightly more correct than assuming whatever comes next is slot 0.

diff --git a/src/evdev.c b/src/evdev.c
index 0cf5aa2..24f52ca 100644 (file)
--- a/src/evdev.c
+++ b/src/evdev.c
@@ -469,7 +469,6 @@ evdev_handle_device(struct evdev_device *device)
                        device->abs.min_y = absinfo.minimum;
                        device->abs.max_y = absinfo.maximum;
                        device->is_mt = 1;
-                       device->mt.slot = 0;
                        device->caps |= EVDEV_TOUCH;
 
                        if (!TEST_BIT(abs_bits, ABS_MT_SLOT)) {
@@ -479,6 +478,11 @@ evdev_handle_device(struct evdev_device *device)
                                                   device->devnode);
                                        return 0;
                                }
+                               device->mt.slot = device->mtdev->caps.slot.value;
+                       } else {
+                               ioctl(device->fd, EVIOCGABS(ABS_MT_SLOT),
+                                     &absinfo);
+                               device->mt.slot = absinfo.value;
                        }
                }
        }