Fixes <https://bugs.gnu.org/39341>.
Reported by Maxim Cournoyer <maxim.cournoyer@gmail.com>.
Until now, as soon as you had selected the keyboard layout in the
Guix System installer, kmscon would start spinning on epoll_wait(2)
calls because of an event on the initial FIFO file
descriptor (corresponding to the fact that the client closed it.)
* gnu/packages/patches/kmscon-runtime-keymap-switch.patch: In
'uxkb_keymap_update_handler', add calls to 'ev_eloop_rm_fd', 'close',
and 'uxkb_dev_keymap_update' In 'uxkb_dev_keymap_update', add call
to 'unlink'.