Re: [PATCH v3 0/3] cgroup: add xattr support

From: Tejun Heo
Date: Fri Jul 20 2012 - 14:10:41 EST

Hello, Hugh.

On Wed, Jul 18, 2012 at 06:11:32PM -0700, Hugh Dickins wrote:
> So systemd is already doing it as I suggested, but finds that awkward in
> some respects, and wants more help from the kernel in synchronization.

Yeah, pretty much.

> Stuffing an unbounded amount of data into cgroupfs xattrs doesn't sound
> the right way to go.
> I wonder if it could be turned completely on its head, and the cgroupfs
> parts be represented in xattrs on a tmpfs hierarchy? The data contents of
> the tmpfs files being entirely up to userspace i.e. systemd in ths case.

Probably not. We can't change the userland-visible cgroup interface
and the cgroup filesystem is unfortunately ***DEEPLY*** (yes, it's
crazily deep) entangled with cgroup core implementation. :(

Longer term goal is to factor out sysfs from kobject / driver model
and share it between cgroup and sysfs. I think it's generally not a
bad idea to support xattr on pseudo filesystems if it isn't too hairy
to support. Low level system management software should be able to
make pretty good use of them.


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