Re: [PATCH 2/3] make clone_children a flag

From: Glauber Costa
Date: Wed Dec 14 2011 - 02:09:53 EST


On 12/14/2011 06:29 AM, Li Zefan wrote:
Tejun Heo wrote:
On Sun, Dec 11, 2011 at 03:45:37PM +0100, Glauber Costa wrote:
There is no reason to have a flags field, and then a separate
bool field just to indicate if the clone_children flag is set.
Make it a flag

Signed-off-by: Glauber Costa<glommer@xxxxxxxxxxxxx>

Doesn't this change how remount conditions are checked?


Well, I was thinking it wouldn't, because I patched all callers. But I forget life is not always that simple: After you mentioned, I checked and we do test for changes in the flag field explicitly on remount. So I missed that, indeed.

Right. Currently we can do this:

# mount -t cgroup xxx /mnt
# mount -o remount,clone_children /mnt

with this patch, the above remount will fail.

But..the current bevaiour of remount is a bit confusing in that remount
with/without "clone_children" has no effect on anything:

# mount -t cgroup -o clone_children xxx /mnt
# cat /mnt/cgroup.clone_children
1
# mount -o remount xxx /mnt
# mount | grep cgroup
xxx on /mnt type cgroup (rw,clone_children)
# cat /mnt/cgroup.clone_children
1

That's indeed confusing, and it comes from the fact that we always inherit clone_children from the parent - which is sane, IMHO. So this flag only has any value in establishing the initial behaviour of the top root cgroup. I wonder then if it wouldn't better to just be explicit and fail in this case ?

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