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SubjectRe: [PATCH 3/9] cgroup: implement generic child / descendant walk macros
Hello, Michal.

On Wed, Nov 07, 2012 at 05:54:57PM +0100, Michal Hocko wrote:
> > +struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
> > + struct cgroup *cgroup)
> > +{
> > + struct cgroup *next;
> > +
> > + WARN_ON_ONCE(!rcu_read_lock_held());
> > +
> > + /* if first iteration, pretend we just visited @cgroup */
> > + if (!pos) {
> > + if (list_empty(&cgroup->children))
> > + return NULL;
> > + pos = cgroup;
> > + }
>
> Is there any specific reason why the root of the tree is excluded?
> This is bit impractical because you have to special case the root
> in the code.

Yeah, thought about including it but decided against it for two
reasons.

* To be consistent with cgroup_for_each_children() - it's a bit weird
for descendants to include self when children don't.

* Iteration root is likely to require different treatment anyway.
e.g. for cgroup_freezer, the root is updated to the specified config
while all the descendants inherit config from its immediate parent.
They are different.

Thanks.

--
tejun


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