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Commit 6f60eade authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: generalize obtaining the handles of and notifying cgroup files 



cgroup core handles creations and removals of cgroup interface files
as described by cftypes.  There are cases where the handle for a given
file instance is necessary, for example, to generate a file modified
event.  Currently, this is handled by explicitly matching the callback
method pointer and storing the file handle manually in
cgroup_add_file().  While this simple approach works for cgroup core
files, it can't for controller interface files.

This patch generalizes cgroup interface file handle handling.  struct
cgroup_file is defined and each cftype can optionally tell cgroup core
to store the file handle by setting ->file_offset.  A file handle
remains accessible as long as the containing css is accessible.

Both "cgroup.procs" and "cgroup.events" are converted to use the new
generic mechanism instead of hooking directly into cgroup_add_file().
Also, cgroup_file_notify() which takes a struct cgroup_file and
generates a file modified event on it is added and replaces explicit
kernfs_notify() invocations.

This generalizes cgroup file handle handling and allows controllers to
generate file modified notifications.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
parent 4df8dc90

include/linux/cgroup-defs.h

+24 −2
Original line number Diff line number Diff line
@@ -83,6 +83,17 @@ enum { 
	__CFTYPE_NOT_ON_DFL	= (1 << 17),	/* not on default hierarchy */

};



/*

 * cgroup_file is the handle for a file instance created in a cgroup which

 * is used, for example, to generate file changed notifications.  This can

 * be obtained by setting cftype->file_offset.

 */

struct cgroup_file {

	/* do not access any fields from outside cgroup core */

	struct list_head node;			/* anchored at css->files */

	struct kernfs_node *kn;

};



/*

 * Per-subsystem/per-cgroup state maintained by the system.  This is the

 * fundamental structural building block that controllers deal with.
@@ -123,6 +134,9 @@ struct cgroup_subsys_state { 
	 */

	u64 serial_nr;



	/* all cgroup_files associated with this css */

	struct list_head files;



	/* percpu_ref killing and RCU release */

	struct rcu_head rcu_head;

	struct work_struct destroy_work;
@@ -226,8 +240,8 @@ struct cgroup { 
	int populated_cnt;



	struct kernfs_node *kn;		/* cgroup kernfs entry */

	struct kernfs_node *procs_kn;	/* kn for "cgroup.procs" */

	struct kernfs_node *events_kn;	/* kn for "cgroup.events" */

	struct cgroup_file procs_file;	/* handle for "cgroup.procs" */

	struct cgroup_file events_file;	/* handle for "cgroup.events" */



	/*

	 * The bitmask of subsystems enabled on the child cgroups.
@@ -335,6 +349,14 @@ struct cftype { 
	/* CFTYPE_* flags */

	unsigned int flags;



	/*

	 * If non-zero, should contain the offset from the start of css to

	 * a struct cgroup_file field.  cgroup will record the handle of

	 * the created file into it.  The recorded handle can be used as

	 * long as the containing css remains accessible.

	 */

	unsigned int file_offset;



	/*

	 * Fields used for internal bookkeeping.  Initialized automatically

	 * during registration.

include/linux/cgroup.h

+13 −0
Original line number Diff line number Diff line
@@ -490,6 +490,19 @@ static inline void pr_cont_cgroup_path(struct cgroup *cgrp) 
	pr_cont_kernfs_path(cgrp->kn);

}



/**

 * cgroup_file_notify - generate a file modified event for a cgroup_file

 * @cfile: target cgroup_file

 *

 * @cfile must have been obtained by setting cftype->file_offset.

 */

static inline void cgroup_file_notify(struct cgroup_file *cfile)

{

	/* might not have been created due to one of the CFTYPE selector flags */

	if (cfile->kn)

		kernfs_notify(cfile->kn);

}



#else /* !CONFIG_CGROUPS */



struct cgroup_subsys_state;

kernel/cgroup.c

+19 −7
Original line number Diff line number Diff line
@@ -612,8 +612,8 @@ static void cgroup_update_populated(struct cgroup *cgrp, bool populated) 
		if (!trigger)

			break;



		if (cgrp->events_kn)

			kernfs_notify(cgrp->events_kn);

		cgroup_file_notify(&cgrp->events_file);



		cgrp = cgroup_parent(cgrp);

	} while (cgrp);

}
@@ -1771,6 +1771,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp) 


	INIT_LIST_HEAD(&cgrp->self.sibling);

	INIT_LIST_HEAD(&cgrp->self.children);

	INIT_LIST_HEAD(&cgrp->self.files);

	INIT_LIST_HEAD(&cgrp->cset_links);

	INIT_LIST_HEAD(&cgrp->pidlists);

	mutex_init(&cgrp->pidlist_mutex);
@@ -2562,7 +2563,7 @@ static int cgroup_procs_write_permission(struct task_struct *task, 
			cgrp = cgroup_parent(cgrp);



		ret = -ENOMEM;

		inode = kernfs_get_inode(sb, cgrp->procs_kn);

		inode = kernfs_get_inode(sb, cgrp->procs_file.kn);

		if (inode) {

			ret = inode_permission(inode, MAY_WRITE);

			iput(inode);
@@ -3253,10 +3254,14 @@ static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp, 
		return ret;

	}



	if (cft->write == cgroup_procs_write)

		cgrp->procs_kn = kn;

	else if (cft->seq_show == cgroup_events_show)

		cgrp->events_kn = kn;

	if (cft->file_offset) {

		struct cgroup_file *cfile = (void *)css + cft->file_offset;



		kernfs_get(kn);

		cfile->kn = kn;

		list_add(&cfile->node, &css->files);

	}



	return 0;

}
@@ -4408,6 +4413,7 @@ static int cgroup_clone_children_write(struct cgroup_subsys_state *css, 
static struct cftype cgroup_dfl_base_files[] = {

	{

		.name = "cgroup.procs",

		.file_offset = offsetof(struct cgroup, procs_file),

		.seq_start = cgroup_pidlist_start,

		.seq_next = cgroup_pidlist_next,

		.seq_stop = cgroup_pidlist_stop,
@@ -4433,6 +4439,7 @@ static struct cftype cgroup_dfl_base_files[] = { 
	{

		.name = "cgroup.events",

		.flags = CFTYPE_NOT_ON_ROOT,

		.file_offset = offsetof(struct cgroup, events_file),

		.seq_show = cgroup_events_show,

	},

	{ }	/* terminate */
@@ -4511,9 +4518,13 @@ static void css_free_work_fn(struct work_struct *work) 
		container_of(work, struct cgroup_subsys_state, destroy_work);

	struct cgroup_subsys *ss = css->ss;

	struct cgroup *cgrp = css->cgroup;

	struct cgroup_file *cfile;



	percpu_ref_exit(&css->refcnt);



	list_for_each_entry(cfile, &css->files, node)

		kernfs_put(cfile->kn);



	if (ss) {

		/* css free path */

		int id = css->id;
@@ -4618,6 +4629,7 @@ static void init_and_link_css(struct cgroup_subsys_state *css, 
	css->ss = ss;

	INIT_LIST_HEAD(&css->sibling);

	INIT_LIST_HEAD(&css->children);

	INIT_LIST_HEAD(&css->files);

	css->serial_nr = css_serial_nr_next++;



	if (cgroup_parent(cgrp)) {