$ for p in `pidof udevd`; do sudo ls -l /proc/$p/fd | wc -l; done | awk '{$s += $1} END { print $s }'
14
$ sudo udevadm trigger --action=change --subsystem-match=block
$ for p in `pidof udevd`; do sudo ls -l /proc/$p/fd | wc -l; done | awk '{$s += $1} END { print $s }'
34
Easy reproducer:
$ for p in `pidof udevd`; do sudo ls -l /proc/$p/fd | wc -l; done | awk '{$s += $1} END { print $s }' match=block
14
$ sudo udevadm trigger --action=change --subsystem-
$ for p in `pidof udevd`; do sudo ls -l /proc/$p/fd | wc -l; done | awk '{$s += $1} END { print $s }'
34