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<base href="https://bugs.freedesktop.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Keys can get stuck permanently when grabbing keyboard with evdev"
href="https://bugs.freedesktop.org/show_bug.cgi?id=101796">101796</a>
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<th>Summary</th>
<td>Keys can get stuck permanently when grabbing keyboard with evdev
</td>
</tr>
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<th>Product</th>
<td>Wayland
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>Linux (All)
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>medium
</td>
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<th>Component</th>
<td>libinput
</td>
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<th>Assignee</th>
<td>wayland-bugs@lists.freedesktop.org
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<th>Reporter</th>
<td>noah.bergbauer@tum.de
</td>
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<p>
<div>
<pre>The logic in evdev.c
(<a href="https://github.com/wayland-project/libinput/blob/688142c8a22c00cfe7b9dec6a71e935b899d8b65/src/evdev.c#L167-L169">https://github.com/wayland-project/libinput/blob/688142c8a22c00cfe7b9dec6a71e935b899d8b65/src/evdev.c#L167-L169</a>)
remembers how many times a key is pressed simultaneously and only emits KEY_UP
events when this counter is incremented to 1 and KEY_DOWN when it is
decremented to 0.
This is problematic as key release events might get dropped, for example if the
keyboard is exclusively grabbed by evdev's EVIOCGRAB while a key is pressed.
This issue is easily reproducible by launching one instance of
libinput-debug-events (or any libinput-based application that reads keyboard
input) and then running this in another terminal:
libinput-debug-events --device /path/to/keyboard --grab & (sleep 1 ; killall
libinput-debug-events)
Because you submit the command by pressing the Enter key and
libinput-debug-events launches fast enough, the release event for your Enter
key happens after the device is grabbed, so the first instance of
libinput-debug-events will not receive it. Because of this bug, the Enter key
is now permanently stuck there as it is always pressed either 1 or 2 times, so
libinput will never send any key events for it again.
(Please note that running this test inside any libinput-based desktop
environment (xf86-input-libinput or Wayland) obviously triggers the same bug
and may force you to restart your window manager.)
In other implementations (xf86-input-evdev, Microsoft Windows), missing release
events are handled gracefully: As pressing an already held key indicates a
missing release event, they just ignore this, so a subsequent key release event
actually releases the key.</pre>
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