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Commit 67f4c36f authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: add cgroup->dummy_css 



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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent f7d58818

include/linux/cgroup.h

+10 −1
Original line number Diff line number Diff line
@@ -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;

}



/**

kernel/cgroup.c

+5 −4
Original line number Diff line number Diff line
@@ -1365,6 +1365,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp) 
	INIT_LIST_HEAD(&cgrp->release_list);

	INIT_LIST_HEAD(&cgrp->pidlists);

	mutex_init(&cgrp->pidlist_mutex);

	cgrp->dummy_css.cgroup = cgrp;

	INIT_LIST_HEAD(&cgrp->event_list);

	spin_lock_init(&cgrp->event_list_lock);

	simple_xattrs_init(&cgrp->xattrs);
@@ -2285,7 +2286,7 @@ static struct cgroup_subsys_state *cgroup_file_css(struct cfent *cfe) 


	if (cft->ss)

		return cgrp->subsys[cft->ss->subsys_id];

	return NULL;

	return &cgrp->dummy_css;

}



/* A buffer size big enough for numbers or short strings */
@@ -2467,7 +2468,7 @@ static int cgroup_file_open(struct inode *inode, struct file *file) 
	 * unpinned either on open failure or release.  This ensures that

	 * @css stays alive for all file operations.

	 */

	if (css && !css_tryget(css))

	if (css->ss && !css_tryget(css))

		return -ENODEV;



	if (cft->read_map || cft->read_seq_string) {
@@ -2477,7 +2478,7 @@ static int cgroup_file_open(struct inode *inode, struct file *file) 
		err = cft->open(inode, file);

	}



	if (css && err)

	if (css->ss && err)

		css_put(css);

	return err;

}
@@ -2491,7 +2492,7 @@ static int cgroup_file_release(struct inode *inode, struct file *file) 


	if (cft->release)

		ret = cft->release(inode, file);

	if (css)

	if (css->ss)

		css_put(css);

	return ret;

}