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Commit 78574cf9 authored by Li Zefan's avatar Li Zefan Committed by Tejun Heo
Browse files

cgroup: implement cgroup_is_descendant() 



A couple controllers want to determine whether two cgroups are in
ancestor/descendant relationship.  As it's more likely that the
descendant is the primary subject of interest and there are other
operations focusing on the descendants, let's ask is_descendent rather
than is_ancestor.

Implementation is trivial as the previous patch guarantees that all
ancestors of a cgroup stay accessible as long as the cgroup is
accessible.

tj: Removed depth optimization, renamed from cgroup_is_ancestor(),
    rewrote descriptions.

Signed-off-by: default avatarLi Zefan <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 415cf07a

include/linux/cgroup.h

+1 −0
Original line number Diff line number Diff line
@@ -439,6 +439,7 @@ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts); 
int cgroup_rm_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);



int cgroup_is_removed(const struct cgroup *cgrp);

bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor);



int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);

kernel/cgroup.c

+20 −0
Original line number Diff line number Diff line
@@ -276,6 +276,26 @@ inline int cgroup_is_removed(const struct cgroup *cgrp) 
	return test_bit(CGRP_REMOVED, &cgrp->flags);

}



/**

 * cgroup_is_descendant - test ancestry

 * @cgrp: the cgroup to be tested

 * @ancestor: possible ancestor of @cgrp

 *

 * Test whether @cgrp is a descendant of @ancestor.  It also returns %true

 * if @cgrp == @ancestor.  This function is safe to call as long as @cgrp

 * and @ancestor are accessible.

 */

bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor)

{

	while (cgrp) {

		if (cgrp == ancestor)

			return true;

		cgrp = cgrp->parent;

	}

	return false;

}

EXPORT_SYMBOL_GPL(cgroup_is_descendant);



/* bits in struct cgroupfs_root flags field */

enum {

	ROOT_NOPREFIX,	/* mounted subsystems have no named prefix */