1. 根目录:
2. net
3. core
4. netclassid_cgroup.c

/*
 * net/core/netclassid_cgroup.c	Classid Cgroupfs Handling
 *
 *		This program is free software; you can redistribute it and/or
 *		modify it under the terms of the GNU General Public License
 *		as published by the Free Software Foundation; either version
 *		2 of the License, or (at your option) any later version.
 *
 * Authors:	Thomas Graf <tgraf@suug.ch>
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/cgroup.h>
#include <linux/fdtable.h>
#include <net/cls_cgroup.h>
#include <net/sock.h>

static inline struct cgroup_cls_state *css_cls_state(struct cgroup_subsys_state *css)
{
	return css ? container_of(css, struct cgroup_cls_state, css) : NULL;
}

struct cgroup_cls_state *task_cls_state(struct task_struct *p)
{
	return css_cls_state(task_css_check(p, net_cls_cgrp_id,
					    rcu_read_lock_bh_held()));
}
EXPORT_SYMBOL_GPL(task_cls_state);

static struct cgroup_subsys_state *
cgrp_css_alloc(struct cgroup_subsys_state *parent_css)
{
	struct cgroup_cls_state *cs;

	cs = kzalloc(sizeof(*cs), GFP_KERNEL);
	if (!cs)
		return ERR_PTR(-ENOMEM);

	return &cs->css;
}

static int cgrp_css_online(struct cgroup_subsys_state *css)
{
	struct cgroup_cls_state *cs = css_cls_state(css);
	struct cgroup_cls_state *parent = css_cls_state(css->parent);

	if (parent)
		cs->classid = parent->classid;

	return 0;
}

static void cgrp_css_free(struct cgroup_subsys_state *css)
{
	kfree(css_cls_state(css));
}

static int update_classid_sock(const void *v, struct file *file, unsigned n)
{
	int err;
	struct socket *sock = sock_from_file(file, &err);

	if (sock)
		sock->sk->sk_classid = (u32)(unsigned long)v;

	return 0;
}

static void update_classid(struct cgroup_subsys_state *css, void *v)
{
	struct css_task_iter it;
	struct task_struct *p;

	css_task_iter_start(css, &it);
	while ((p = css_task_iter_next(&it))) {
		task_lock(p);
		iterate_fd(p->files, 0, update_classid_sock, v);
		task_unlock(p);
	}
	css_task_iter_end(&it);
}

static void cgrp_attach(struct cgroup_taskset *tset)
{
	struct cgroup_subsys_state *css;

	cgroup_taskset_first(tset, &css);
	update_classid(css,
		       (void *)(unsigned long)css_cls_state(css)->classid);
}

static u64 read_classid(struct cgroup_subsys_state *css, struct cftype *cft)
{
	return css_cls_state(css)->classid;
}

static int write_classid(struct cgroup_subsys_state *css, struct cftype *cft,
			 u64 value)
{
	struct cgroup_cls_state *cs = css_cls_state(css);

	cs->classid = (u32)value;

	update_classid(css, (void *)(unsigned long)cs->classid);
	return 0;
}

static struct cftype ss_files[] = {
	{
		.name		= "classid",
		.read_u64	= read_classid,
		.write_u64	= write_classid,
	},
	{ }	/* terminate */
};

struct cgroup_subsys net_cls_cgrp_subsys = {
	.css_alloc		= cgrp_css_alloc,
	.css_online		= cgrp_css_online,
	.css_free		= cgrp_css_free,
	.attach			= cgrp_attach,
	.legacy_cftypes		= ss_files,
};