| Re: [PATCH 2/3] make clone_children a flag [message #44546 is a reply to message #44543] |
Wed, 14 December 2011 07:09   |
Glauber Costa
Messages: 916
Registered: October 2011
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Senior Member |
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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@parallels.com>
>>
>> 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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