udev rules may get missed due to rule caching

Submission type

• Bug report

systemd version the issue has been seen with

Tested with 229

Used distribution

RHEL, Fedora, LFS

In case of bug report: Expected behaviour you didn't see

Newly added rules are immediately effective

In case of bug report: Unexpected behaviour you saw

Rules may get ignored due to caching

In case of bug report: Steps to reproduce the problem

#!/bin/bash                                                                                                                                                                              

chown root.root /dev/zero
echo "KERNEL==\"zero\", GROUP=\"nobody\"" > 80-zero.rules

udevadm trigger --sysname-match=zero --action=add
cp -v 80-zero.rules /usr/lib/udev/rules.d/
test "$1" && udevadm control --reload
udevadm trigger --sysname-match=zero --action=add
ls -l /dev/zero
sleep 1
udevadm trigger --sysname-match=zero --action=add
ls -l /dev/zero
sleep 1
udevadm trigger --sysname-match=zero --action=add
ls -l /dev/zero
sleep 1
udevadm trigger --sysname-match=zero --action=add
ls -l /dev/zero
sleep 1
udevadm trigger --sysname-match=zero --action=add
ls -l /dev/zero
sleep 1
udevadm trigger --sysname-match=zero --action=add
ls -l /dev/zero
sleep 1
udevadm trigger --sysname-match=zero --action=add
ls -l /dev/zero

[root@kha foo2]# ./utest.sh
‘80-zero.rules’ -> ‘/usr/lib/udev/rules.d/80-zero.rules’
crw-rw-rw-. 1 root root 1, 5 27. 4. 13:39 /dev/zero
crw-rw-rw-. 1 root root 1, 5 27. 4. 13:39 /dev/zero
crw-rw-rw-. 1 root root 1, 5 27. 4. 13:39 /dev/zero
crw-rw-rw-. 1 root root 1, 5 27. 4. 13:39 /dev/zero
crw-rw-rw-. 1 root nobody 1, 5 27. 4. 13:39 /dev/zero
crw-rw-rw-. 1 root nobody 1, 5 27. 4. 13:39 /dev/zero
crw-rw-rw-. 1 root nobody 1, 5 27. 4. 13:39 /dev/zero
[root@kha foo2]# 

Start by reproducing the behavior with the shell script in the issue, then trace udev's rule reload and rule-cache handling. Confirm when a newly installed rule becomes effective and verify that the expected device ownership is applied immediately after reload.