[RFC] Prefixing cgroup generic control filenames with "cgroup."

[Paul Menage]

All control files created by cgroup subsystems are given a prefix
corresponding to their subsystem name. But control files provided by
cgroups itself have no prefix. Currently that set of files is just
"tasks", "notify_on_release" and "release_agent", but that set is
likely to expand in the future. To reduce the risk of clashes, it
would make sense to prefix these files and any future ones with the
"cgroup." prefix.

The only reason that I can see *not* to do this would be for
compatibility with 2.6.24. Do people think this is a strong enough
reason to leave the existing names? If distros are planning to ship
products based on 2.6.24, presumably they'd be adding their own
patches anyway, so they could add a trivial prefix change patch too.
(I realise this discussion would have been more useful *before* 2.6.24
shipped, but I didn't quite get round to it ...)

A compromise might be to keep "tasks" unprefixed, and say that future
names get the "cgroup." prefix; in this case I'd be inclined to add
the prefix to notify_on_release and release_agent on the grounds that
there's much less chance of breaking anyone with those files since (I
suspect) they're much less used.

Note that if you mount a cgroup filesystem with the "noprefix" option,
which is what the cpuset filesystem wrapper does, no subsystems have
prefixes, and in this case the "cgroup." prefix wouldn't be used
either. So this doesn't affect any users that explicitly mount cpusets
rather than cgroups.

Thoughts?

Paul
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