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/*

 * ns_cgroup.c - namespace cgroup subsystem

 *

 * Copyright 2006, 2007 IBM Corp

 */

#include <linux/module.h>

#include <linux/cgroup.h>

#include <linux/fs.h>

struct ns_cgroup {

        struct cgroup_subsys_state css;

        spinlock_t lock;

};

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)

{

        return cgroup_clone(task, &ns_subsys);

}

/*

 * Rules:

 *   1. you can only enter a cgroup which is a child 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)

{

        struct cgroup *orig;

        if (current != task) {

                if (!capable(CAP_SYS_ADMIN))

                        return -EPERM;

                if (!cgroup_is_descendant(new_cgroup))

                        return -EPERM;

        }

        if (atomic_read(&new_cgroup->count) != 0)

                return -EPERM;

        orig = task_cgroup(task, ns_subsys_id);

        if (orig && orig != new_cgroup->parent)

                return -EPERM;

        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))

                return ERR_PTR(-EPERM);

        ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);

        if (!ns_cgroup)

                return ERR_PTR(-ENOMEM);

        spin_lock_init(&ns_cgroup->lock);

        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,

};