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cgroup: add cgroup->dummy_css

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cgroup subsystem API is being converted to use css
(cgroup_subsys_state) as the main handle, which makes things a bit
awkward for subsystem agnostic core features - the "cgroup.*"
interface files and various iterations - a bit awkward as they don't
have a css to use.

This patch adds cgroup->dummy_css which has NULL ->ss and whose only
role is pointing back to the cgroup.  This will be used to support
subsystem agnostic features on the coming css based API.

css_parent() is updated to handle dummy_css's.  Note that css will
soon grow its own ->parent field and css_parent() will be made
trivial.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo
2013-08-08 20:11:24 -04:00
parent f7d58818ba
commit 67f4c36f83
2 changed files with 15 additions and 5 deletions
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11
include/linux/cgroup.h
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@@ -225,6 +225,9 @@ struct cgroup {
struct list_head pidlists;
struct mutex pidlist_mutex;
/* dummy css with NULL ->ss, points back to this cgroup */
struct cgroup_subsys_state dummy_css;
/* For css percpu_ref killing and RCU-protected deletion */
struct rcu_head rcu_head;
struct work_struct destroy_work;
@@ -668,7 +671,13 @@ struct cgroup_subsys_state *css_parent(struct cgroup_subsys_state *css)
{
struct cgroup *parent_cgrp = css->cgroup->parent;
return parent_cgrp ? parent_cgrp->subsys[css->ss->subsys_id] : NULL;
if (!parent_cgrp)
return NULL;
if (css->ss)
return parent_cgrp->subsys[css->ss->subsys_id];
else
return &parent_cgrp->dummy_css;
}
/**