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evdev: track KEY_SYSRQ frames and pass them even as repeat frames

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Alt+Printscreen aka KEY_LEFTALT + KEY_SYSRQ is emulated by the kernel
and always posted with SYN_REPORT 1, see
drivers/tty/sysrq.c:sysrq_reinject_alt_sysrq()

The actual sequence when pressing Alt + Printscreen is to release Alt
first, then press it again:
- evdev:
    - [ 10, 674010,   1,  56,       0] # EV_KEY / KEY_LEFTALT               0
    - [ 10, 674010,   0,   0,       0] # ------------ SYN_REPORT (0) ---------- +2861ms
  - evdev:
    - [ 10, 674030,   1,  56,       1] # EV_KEY / KEY_LEFTALT               1
    - [ 10, 674030,   1,  99,       1] # EV_KEY / KEY_SYSRQ                 1
    - [ 10, 674030,   0,   0,       1] # ------------ SYN_REPORT (1) ---------- +0ms
  - evdev:
    - [ 10, 674031,   1,  99,       0] # EV_KEY / KEY_SYSRQ                 0
    - [ 10, 674031,   1,  56,       0] # EV_KEY / KEY_LEFTALT               0
    - [ 10, 674031,   0,   0,       1] # ------------ SYN_REPORT (1) ---------- +0ms

Handle that special case so we get our printscreen key to work as
expected anymore.

Fixes: 9a9466b6a9 ("evdev: discard any frame with EV_SYN SYN_REPORT 1")
Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1273>
This commit is contained in:
Peter Hutterer 2025-07-15 21:29:43 +10:00
parent ccc798808a
commit 7140f13d82
2 changed files with 69 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

13
src/evdev.c
View file

@ -1043,6 +1043,7 @@ evdev_device_dispatch(void *data)
struct input_event ev;
int rc;
bool once = false;
bool had_sysrq = false;
_unref_(evdev_frame) *frame = evdev_frame_new(64);
/* If the compositor is repainting, this function is called only once
@ -1083,17 +1084,27 @@ evdev_device_dispatch(void *data)
device,
"event frame overflow, discarding events.\n");
}
/* Alt+Printscreen is always a repeat frame, see
* drivers/tty/sysrq.c:sysrq_reinject_alt_sysrq() in the
* kernel
*/
if (ev.type == EV_KEY && ev.code == KEY_SYSRQ)
had_sysrq = true;
if (ev.type == EV_SYN && ev.code == SYN_REPORT) {
/* A SYN_REPORT 1 event is a kernel-inserted
* auto-repeat. Nothing in libinput cares about kernel
* repeats and the inserted frame causes issues with
* timestamp deltas (see e.g. #1145)
*
* (well, except Alt+Printscreen (KEY_SYSRQ))
*/
if (ev.value != 1)
if (ev.value != 1 || had_sysrq)
evdev_device_dispatch_frame(libinput,
device,
frame);
evdev_frame_reset(frame);
had_sysrq = false;
}
} else if (rc == -ENODEV) {
evdev_device_remove(device);

57
test/test-keyboard.c
View file

@ -468,6 +468,61 @@ START_TEST(keyboard_no_scroll)
}
END_TEST
START_TEST(keyboard_alt_printscreen)
{
struct litest_device *dev = litest_current_device();
struct libinput *li = dev->libinput;
litest_drain_events(li);
/* repeat frame, ignored */
litest_event(dev, EV_KEY, KEY_A, 1);
litest_event(dev, EV_SYN, SYN_REPORT, 1);
litest_dispatch(li);
litest_assert_empty_queue(li);
/* not a repeat frame */
litest_event(dev, EV_KEY, KEY_LEFTALT, 1);
litest_event(dev, EV_SYN, SYN_REPORT, 0);
litest_dispatch(li);
litest_assert_key_event(li, KEY_LEFTALT, LIBINPUT_KEY_STATE_PRESSED);
/* normal repeat frame, ignored */
litest_event(dev, EV_KEY, KEY_LEFTALT, 2);
litest_event(dev, EV_SYN, SYN_REPORT, 1);
litest_dispatch(li);
litest_assert_empty_queue(li);
/* not repeat frame */
litest_event(dev, EV_KEY, KEY_LEFTALT, 0);
litest_event(dev, EV_SYN, SYN_REPORT, 0);
litest_dispatch(li);
litest_assert_key_event(li, KEY_LEFTALT, LIBINPUT_KEY_STATE_RELEASED);
/* special alt+printscreen repeat frame, *not* ignored */
litest_event(dev, EV_KEY, KEY_LEFTALT, 1);
litest_event(dev, EV_KEY, KEY_SYSRQ, 1);
litest_event(dev, EV_SYN, SYN_REPORT, 1);
litest_dispatch(li);
/* special alt+printscreen repeat frame, *not* ignored */
litest_event(dev, EV_KEY, KEY_LEFTALT, 0);
litest_event(dev, EV_KEY, KEY_SYSRQ, 0);
litest_event(dev, EV_SYN, SYN_REPORT, 1);
litest_dispatch(li);
/* Note: the kernel doesn't release the key combo until both keys are released
* and the order is reshuffled so we have alt down, sysrq down, sysrq up, alt up
*/
litest_assert_key_event(li, KEY_LEFTALT, LIBINPUT_KEY_STATE_PRESSED);
litest_assert_key_event(li, KEY_SYSRQ, LIBINPUT_KEY_STATE_PRESSED);
litest_assert_key_event(li, KEY_SYSRQ, LIBINPUT_KEY_STATE_RELEASED);
litest_assert_key_event(li, KEY_LEFTALT, LIBINPUT_KEY_STATE_RELEASED);
litest_assert_empty_queue(li);
}
END_TEST
TEST_COLLECTION(keyboard)
{
/* clang-format off */
@ -484,5 +539,7 @@ TEST_COLLECTION(keyboard)
litest_add(keyboard_leds, LITEST_ANY, LITEST_ANY);
litest_add(keyboard_no_scroll, LITEST_KEYS, LITEST_WHEEL);
litest_add_for_device(keyboard_alt_printscreen, LITEST_KEYBOARD);
/* clang-format on */
}