Files in /dev/cpuset renamed?

Question

I'm working on some old scripts that deal with cpusets, porting to openSUSE. The scripts worked fine with openSUSE 15.5, but now with 15.6 they fail because the /dev/cpuset files they expect aren't there. In fact, the files are all there, but they've lost the prefix cpuset. in their names.

For instance, for a cpuset named sys, the scripts expect to manipulate /dev/cpuset/sys/cpuset.cpus, but the actual file seems to be named /dev/cpuset/sys/cpus. This pattern continues for all thirteen files that on openSUSE 15.5 (and older systems) had names starting with cpuset.; the same files are there, but without the cpuset. prefix.

Looking at docs.kernel.org's reference page, the cpuset.* naming is what is documented. Any idea where the files missing the cpuset. prefix came from?

More info: here's the full /dev/cpuset/sys directory (where sys is a cpuset name) on a openSUSE Leap 15.5 machine:

devuser@product:/dev/cpuset/sys> ls -al
total 0
drwxr-xr-x 2 root root 0 Feb 18 14:07 .
dr-xr-xr-x 3 root root 0 Feb 18 14:03 ..
-rw-r--r-- 1 root root 0 Feb 18 14:07 cgroup.clone_children
-rw-r--r-- 1 root root 0 Feb 18 14:07 cgroup.procs
-rw-r--r-- 1 root root 0 Feb 18 14:07 cpuset.cpu_exclusive
-rw-r--r-- 1 root root 0 Feb 18 14:07 cpuset.cpus
-r--r--r-- 1 root root 0 Feb 18 14:07 cpuset.effective_cpus
-r--r--r-- 1 root root 0 Feb 18 14:07 cpuset.effective_mems
-rw-r--r-- 1 root root 0 Feb 18 14:07 cpuset.mem_exclusive
-rw-r--r-- 1 root root 0 Feb 18 14:07 cpuset.mem_hardwall
-rw-r--r-- 1 root root 0 Feb 18 14:07 cpuset.memory_migrate
-r--r--r-- 1 root root 0 Feb 18 14:07 cpuset.memory_pressure
-rw-r--r-- 1 root root 0 Feb 18 14:07 cpuset.memory_spread_page
-rw-r--r-- 1 root root 0 Feb 18 14:07 cpuset.memory_spread_slab
-rw-r--r-- 1 root root 0 Feb 18 14:07 cpuset.mems
-rw-r--r-- 1 root root 0 Feb 18 14:07 cpuset.sched_load_balance
-rw-r--r-- 1 root root 0 Feb 18 14:07 cpuset.sched_relax_domain_level
-rw-r--r-- 1 root root 0 Feb 18 14:07 notify_on_release
-rw-r--r-- 1 root root 0 Feb 18 14:07 tasks
devuser@product:/dev/cpuset/sys> 

And here's the same directory on an openSUSE 15.6 machine:

devuser@product:/dev/cpuset/sys> ls -al
total 0
drwxr-xr-x 2 root root 0 Feb 18 11:25 .
dr-xr-xr-x 5 root root 0 Feb 18 11:25 ..
-rw-r--r-- 1 root root 0 Feb 18 11:29 cgroup.clone_children
-rw-r--r-- 1 root root 0 Feb 18 11:29 cgroup.procs
-rw-r--r-- 1 root root 0 Feb 18 11:29 cpu_exclusive
-rw-r--r-- 1 root root 0 Feb 18 11:29 cpus
-r--r--r-- 1 root root 0 Feb 18 11:29 effective_cpus
-r--r--r-- 1 root root 0 Feb 18 11:29 effective_mems
-rw-r--r-- 1 root root 0 Feb 18 11:29 mem_exclusive
-rw-r--r-- 1 root root 0 Feb 18 11:29 mem_hardwall
-rw-r--r-- 1 root root 0 Feb 18 11:29 memory_migrate
-r--r--r-- 1 root root 0 Feb 18 11:29 memory_pressure
-rw-r--r-- 1 root root 0 Feb 18 11:29 memory_spread_page
-rw-r--r-- 1 root root 0 Feb 18 11:29 memory_spread_slab
-rw-r--r-- 1 root root 0 Feb 18 11:29 mems
-rw-r--r-- 1 root root 0 Feb 18 11:29 notify_on_release
-rw-r--r-- 1 root root 0 Feb 18 11:29 sched_load_balance
-rw-r--r-- 1 root root 0 Feb 18 11:29 sched_relax_domain_level
-rw-r--r-- 1 root root 0 Feb 18 12:41 tasks
devuser@product:/dev/cpuset/sys> 

So, exactly the same set of files, except that where Leap 15.5 has a cpuset. prefix on thirteen of file files, Leap 15.6 has the same files but with cpuset. removed.

Edit: here's how I made the cpuset directory on the Leap 15.6 system. On a freshly-rebooted system:

devuser@product:~> ls /dev/cpuset
ls: cannot access '/dev/cpuset': No such file or directory
devuser@product:~> sudo mkdir /dev/cpuset
[sudo] password for root: 
devuser@product:~> sudo mount -t cpuset none /dev/cpuset
devuser@product:~> sudo mkdir /dev/cpuset/sys
devuser@product:~> ls /dev/cpuset/sys
cgroup.clone_children  mem_exclusive       mems
cgroup.procs           mem_hardwall        notify_on_release
cpu_exclusive          memory_migrate      sched_load_balance
cpus                   memory_pressure     sched_relax_domain_level
effective_cpus         memory_spread_page  tasks
effective_mems         memory_spread_slab
devuser@product:~> 

Answer 1

OP also reports the following lines in /proc/mounts :

cgroup2 /sys/fs/cgroup cgroup2 rw,nosuid,nodev,noexec,relatime,nsdelegate,memory_recursiveprot 0 0
none /dev/cpuset cgroup rw,relatime,cpuset,noprefix,release_agent=/sbin/cpuset_release_agent 0 0

The later is the mount at /dev/cpuset. It is set to show only the cpuset entries of cgroup. The noprefix clause is almost certainly the cause of OP's change.

To undo this, try:

# umount /dev/cpuset
# mount -t cgroup -o cpuset,release_agent=/sbin/cpuset_release_agent none /dev/cpuset

I will admit to know knowing what "release_agent=" does.

To undo it permanently... might be tricky, as /dev/ is mounted and managed oddly. But you could try a relevant line in /etc/fstab

none /dev/cpuset cgroup cpuset,release_agent=/sbin/cpuset_release_agent 0 0

Answer 2

It turns out that, between openSUSE 15.5 and openSUSE 16, systemd was upgraded. One significant change: systemd now uses cgroup v2 by default. This changes a number of paths, including those used by cpuset (which is emulated by cgroup).

References:

• https://en.wikipedia.org/wiki/Cgroups
• https://docs.kernel.org/admin-guide/cgroup-v2.html
• https://forums.opensuse.org/t/cpuset-files-in-dev-renamed/182730/7