Missed some rows

Posted May 4, 2011 5:44 UTC (Wed) by Cyberax (✭ supporter ✭, #52523)
In reply to: Missed some rows by wahern
Parent article: Poettering: Why systemd?

That's a trick question.

You need to somehow have a unique process handle, which PID is definitely not. On Linux it can be done using the /proc/PID/ directory. The sequence would be:
1) Change current directory to /proc/PID
2) Look around and check that this PID is still the correct one. That's safe because if the process its /proc/PID directory becomes empty - and stays that way.
3) Write to /proc/PID/cgroup.

Of course, it's better to create a process directly in the required group in the first place.

Missed some rows

Posted May 4, 2011 8:26 UTC (Wed) by wahern (subscriber, #37304) [Link]

I thought /proc/$PID/cgroup was read-only; to add a process to a group you needed to write to /dev/cgroup/$TASK/tasks. In such case, you're left with a race condition. (I tried confirming or disproving this, but can't even get the example in cgroups.txt to work.)

My proposal was to make PID a unique quasi-handle the same way random UUIDs are unique.