/*
   * ns_cgroup.c - namespace cgroup subsystem
   *
   * Copyright 2006, 2007 IBM Corp
   */
  
  #include <linux/module.h>
  #include <linux/cgroup.h>
  #include <linux/fs.h>

  #include <linux/proc_fs.h>

  #include <linux/slab.h>

  #include <linux/nsproxy.h>

  
  struct ns_cgroup {
  	struct cgroup_subsys_state css;

  };
  
  struct cgroup_subsys ns_subsys;
  
  static inline struct ns_cgroup *cgroup_to_ns(
  		struct cgroup *cgroup)
  {
  	return container_of(cgroup_subsys_state(cgroup, ns_subsys_id),
  			    struct ns_cgroup, css);
  }

  int ns_cgroup_clone(struct task_struct *task, struct pid *pid)

  {

  	char name[PROC_NUMBUF];
  
  	snprintf(name, PROC_NUMBUF, "%d", pid_vnr(pid));
  	return cgroup_clone(task, &ns_subsys, name);

  }
  
  /*
   * Rules:

   *   1. you can only enter a cgroup which is a descendant of your current

   *     cgroup
   *   2. you can only place another process into a cgroup if
   *     a. you have CAP_SYS_ADMIN
   *     b. your cgroup is an ancestor of task's destination cgroup
   *       (hence either you are in the same cgroup as task, or in an
   *        ancestor cgroup thereof)
   */

  static int ns_can_attach(struct cgroup_subsys *ss, struct cgroup *new_cgroup,
  			 struct task_struct *task, bool threadgroup)

  {

  	if (current != task) {
  		if (!capable(CAP_SYS_ADMIN))
  			return -EPERM;

  		if (!cgroup_is_descendant(new_cgroup, current))

  			return -EPERM;
  	}

  	if (!cgroup_is_descendant(new_cgroup, task))

  		return -EPERM;

  	if (threadgroup) {
  		struct task_struct *c;
  		rcu_read_lock();
  		list_for_each_entry_rcu(c, &task->thread_group, thread_group) {
  			if (!cgroup_is_descendant(new_cgroup, c)) {
  				rcu_read_unlock();
  				return -EPERM;
  			}
  		}
  		rcu_read_unlock();
  	}

  	return 0;
  }
  
  /*
   * Rules: you can only create a cgroup if
   *     1. you are capable(CAP_SYS_ADMIN)
   *     2. the target cgroup is a descendant of your own cgroup
   */
  static struct cgroup_subsys_state *ns_create(struct cgroup_subsys *ss,
  						struct cgroup *cgroup)
  {
  	struct ns_cgroup *ns_cgroup;
  
  	if (!capable(CAP_SYS_ADMIN))
  		return ERR_PTR(-EPERM);

  	if (!cgroup_is_descendant(cgroup, current))

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

  	return &ns_cgroup->css;
  }
  
  static void ns_destroy(struct cgroup_subsys *ss,
  			struct cgroup *cgroup)
  {
  	struct ns_cgroup *ns_cgroup;
  
  	ns_cgroup = cgroup_to_ns(cgroup);
  	kfree(ns_cgroup);
  }
  
  struct cgroup_subsys ns_subsys = {
  	.name = "ns",
  	.can_attach = ns_can_attach,
  	.create = ns_create,
  	.destroy  = ns_destroy,
  	.subsys_id = ns_subsys_id,
  };