cgroup.c

			int i;
			const char *name = token + 5;
			/* Can't specify an empty name */
			if (!strlen(name))
				return -EINVAL;
			/* Must match [\w.-]+ */
			for (i = 0; i < strlen(name); i++) {
				char c = name[i];
				if (isalnum(c))
					continue;
				if ((c == '.') || (c == '-') || (c == '_'))
					continue;
				return -EINVAL;
			}
			/* Specifying two names is forbidden */
			if (opts->name)
				return -EINVAL;
			opts->name = kstrndup(name,
					      MAX_CGROUP_ROOT_NAMELEN,
					      GFP_KERNEL);
			if (!opts->name)
				return -ENOMEM;
		} else {
			struct cgroup_subsys *ss;
			int i;
			for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
				ss = subsys[i];
				if (!strcmp(token, ss->name)) {
					if (!ss->disabled)
						set_bit(i, &opts->subsys_bits);
					break;
				}
			}
			if (i == CGROUP_SUBSYS_COUNT)
				return -ENOENT;
		}
	}

	/* Consistency checks */

	/*
	 * Option noprefix was introduced just for backward compatibility
	 * with the old cpuset, so we allow noprefix only if mounting just
	 * the cpuset subsystem.
	 */
	if (test_bit(ROOT_NOPREFIX, &opts->flags) &&
	    (opts->subsys_bits & mask))
		return -EINVAL;


	/* Can't specify "none" and some subsystems */
	if (opts->subsys_bits && opts->none)
		return -EINVAL;

	/*
	 * We either have to specify by name or by subsystems. (So all
	 * empty hierarchies must have a name).
	 */
	if (!opts->subsys_bits && !opts->name)
		return -EINVAL;

	return 0;
}

static int cgroup_remount(struct super_block *sb, int *flags, char *data)
{
	int ret = 0;
	struct cgroupfs_root *root = sb->s_fs_info;
	struct cgroup *cgrp = &root->top_cgroup;
	struct cgroup_sb_opts opts;

	lock_kernel();
	mutex_lock(&cgrp->dentry->d_inode->i_mutex);
	mutex_lock(&cgroup_mutex);

	/* See what subsystems are wanted */
	ret = parse_cgroupfs_options(data, &opts);
	if (ret)
		goto out_unlock;

	/* Don't allow flags to change at remount */
	if (opts.flags != root->flags) {
		ret = -EINVAL;
		goto out_unlock;
	}

	/* Don't allow name to change at remount */
	if (opts.name && strcmp(opts.name, root->name)) {
		ret = -EINVAL;
		goto out_unlock;
	}

	ret = rebind_subsystems(root, opts.subsys_bits);
	if (ret)
		goto out_unlock;

	/* (re)populate subsystem files */
	cgroup_populate_dir(cgrp);

	if (opts.release_agent)
		strcpy(root->release_agent_path, opts.release_agent);
 out_unlock:
	kfree(opts.release_agent);
	kfree(opts.name);
	mutex_unlock(&cgroup_mutex);
	mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
	unlock_kernel();
	return ret;
}

static const struct super_operations cgroup_ops = {
	.statfs = simple_statfs,
	.drop_inode = generic_delete_inode,
	.show_options = cgroup_show_options,
	.remount_fs = cgroup_remount,
};

static void init_cgroup_housekeeping(struct cgroup *cgrp)
{
	INIT_LIST_HEAD(&cgrp->sibling);
	INIT_LIST_HEAD(&cgrp->children);
	INIT_LIST_HEAD(&cgrp->css_sets);
	INIT_LIST_HEAD(&cgrp->release_list);
	init_rwsem(&(cgrp->tasks.mutex));
	init_rwsem(&(cgrp->procs.mutex));
}

static void init_cgroup_root(struct cgroupfs_root *root)
{
	struct cgroup *cgrp = &root->top_cgroup;
	INIT_LIST_HEAD(&root->subsys_list);
	INIT_LIST_HEAD(&root->root_list);
	root->number_of_cgroups = 1;
	cgrp->root = root;
	cgrp->top_cgroup = cgrp;
	init_cgroup_housekeeping(cgrp);
}

static bool init_root_id(struct cgroupfs_root *root)
{
	int ret = 0;

	do {
		if (!ida_pre_get(&hierarchy_ida, GFP_KERNEL))
			return false;
		spin_lock(&hierarchy_id_lock);
		/* Try to allocate the next unused ID */
		ret = ida_get_new_above(&hierarchy_ida, next_hierarchy_id,
					&root->hierarchy_id);
		if (ret == -ENOSPC)
			/* Try again starting from 0 */
			ret = ida_get_new(&hierarchy_ida, &root->hierarchy_id);
		if (!ret) {
			next_hierarchy_id = root->hierarchy_id + 1;
		} else if (ret != -EAGAIN) {
			/* Can only get here if the 31-bit IDR is full ... */
			BUG_ON(ret);
		}
		spin_unlock(&hierarchy_id_lock);
	} while (ret);
	return true;
}

static int cgroup_test_super(struct super_block *sb, void *data)
{
	struct cgroup_sb_opts *opts = data;
	struct cgroupfs_root *root = sb->s_fs_info;

	/* If we asked for a name then it must match */
	if (opts->name && strcmp(opts->name, root->name))
		return 0;

	/*
	 * If we asked for subsystems (or explicitly for no
	 * subsystems) then they must match
	 */
	if ((opts->subsys_bits || opts->none)
	    && (opts->subsys_bits != root->subsys_bits))
		return 0;

	return 1;
}

static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
{
	struct cgroupfs_root *root;

	if (!opts->subsys_bits && !opts->none)
		return NULL;

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

	if (!init_root_id(root)) {
		kfree(root);
		return ERR_PTR(-ENOMEM);
	}
	init_cgroup_root(root);

	root->subsys_bits = opts->subsys_bits;
	root->flags = opts->flags;
	if (opts->release_agent)
		strcpy(root->release_agent_path, opts->release_agent);
	if (opts->name)
		strcpy(root->name, opts->name);
	return root;
}

static void cgroup_drop_root(struct cgroupfs_root *root)
{
	if (!root)
		return;

	BUG_ON(!root->hierarchy_id);
	spin_lock(&hierarchy_id_lock);
	ida_remove(&hierarchy_ida, root->hierarchy_id);
	spin_unlock(&hierarchy_id_lock);
	kfree(root);
}

static int cgroup_set_super(struct super_block *sb, void *data)
{
	int ret;
	struct cgroup_sb_opts *opts = data;

	/* If we don't have a new root, we can't set up a new sb */
	if (!opts->new_root)
		return -EINVAL;

	BUG_ON(!opts->subsys_bits && !opts->none);

	ret = set_anon_super(sb, NULL);
	if (ret)
		return ret;

	sb->s_fs_info = opts->new_root;
	opts->new_root->sb = sb;

	sb->s_blocksize = PAGE_CACHE_SIZE;
	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
	sb->s_magic = CGROUP_SUPER_MAGIC;
	sb->s_op = &cgroup_ops;

	return 0;
}

static int cgroup_get_rootdir(struct super_block *sb)
{
	struct inode *inode =
		cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
	struct dentry *dentry;

	if (!inode)
		return -ENOMEM;

	inode->i_fop = &simple_dir_operations;
	inode->i_op = &cgroup_dir_inode_operations;
	/* directories start off with i_nlink == 2 (for "." entry) */
	inc_nlink(inode);
	dentry = d_alloc_root(inode);
	if (!dentry) {
		iput(inode);
		return -ENOMEM;
	}
	sb->s_root = dentry;
	return 0;
}

static int cgroup_get_sb(struct file_system_type *fs_type,
			 int flags, const char *unused_dev_name,
			 void *data, struct vfsmount *mnt)
{
	struct cgroup_sb_opts opts;
	struct cgroupfs_root *root;
	int ret = 0;
	struct super_block *sb;
	struct cgroupfs_root *new_root;

	/* First find the desired set of subsystems */
	ret = parse_cgroupfs_options(data, &opts);
	if (ret)
		goto out_err;

	/*
	 * Allocate a new cgroup root. We may not need it if we're
	 * reusing an existing hierarchy.
	 */
	new_root = cgroup_root_from_opts(&opts);
	if (IS_ERR(new_root)) {
		ret = PTR_ERR(new_root);
		goto out_err;
	}
	opts.new_root = new_root;

	/* Locate an existing or new sb for this hierarchy */
	sb = sget(fs_type, cgroup_test_super, cgroup_set_super, &opts);
	if (IS_ERR(sb)) {
		ret = PTR_ERR(sb);
		cgroup_drop_root(opts.new_root);
		goto out_err;
	}

	root = sb->s_fs_info;
	BUG_ON(!root);
	if (root == opts.new_root) {
		/* We used the new root structure, so this is a new hierarchy */
		struct list_head tmp_cg_links;
		struct cgroup *root_cgrp = &root->top_cgroup;
		struct inode *inode;
		struct cgroupfs_root *existing_root;
		int i;

		BUG_ON(sb->s_root != NULL);

		ret = cgroup_get_rootdir(sb);
		if (ret)
			goto drop_new_super;
		inode = sb->s_root->d_inode;

		mutex_lock(&inode->i_mutex);
		mutex_lock(&cgroup_mutex);

		if (strlen(root->name)) {
			/* Check for name clashes with existing mounts */
			for_each_active_root(existing_root) {
				if (!strcmp(existing_root->name, root->name)) {
					ret = -EBUSY;
					mutex_unlock(&cgroup_mutex);
					mutex_unlock(&inode->i_mutex);
					goto drop_new_super;
				}
			}
		}

		/*
		 * We're accessing css_set_count without locking
		 * css_set_lock here, but that's OK - it can only be
		 * increased by someone holding cgroup_lock, and
		 * that's us. The worst that can happen is that we
		 * have some link structures left over
		 */
		ret = allocate_cg_links(css_set_count, &tmp_cg_links);
		if (ret) {
			mutex_unlock(&cgroup_mutex);
			mutex_unlock(&inode->i_mutex);
			goto drop_new_super;
		}

		ret = rebind_subsystems(root, root->subsys_bits);
		if (ret == -EBUSY) {
			mutex_unlock(&cgroup_mutex);
			mutex_unlock(&inode->i_mutex);
			free_cg_links(&tmp_cg_links);
			goto drop_new_super;
		}

		/* EBUSY should be the only error here */
		BUG_ON(ret);

		list_add(&root->root_list, &roots);
		root_count++;

		sb->s_root->d_fsdata = root_cgrp;
		root->top_cgroup.dentry = sb->s_root;

		/* Link the top cgroup in this hierarchy into all
		 * the css_set objects */
		write_lock(&css_set_lock);
		for (i = 0; i < CSS_SET_TABLE_SIZE; i++) {
			struct hlist_head *hhead = &css_set_table[i];
			struct hlist_node *node;
			struct css_set *cg;

			hlist_for_each_entry(cg, node, hhead, hlist)
				link_css_set(&tmp_cg_links, cg, root_cgrp);
		}
		write_unlock(&css_set_lock);

		free_cg_links(&tmp_cg_links);

		BUG_ON(!list_empty(&root_cgrp->sibling));
		BUG_ON(!list_empty(&root_cgrp->children));
		BUG_ON(root->number_of_cgroups != 1);

		cgroup_populate_dir(root_cgrp);
		mutex_unlock(&cgroup_mutex);
		mutex_unlock(&inode->i_mutex);
	} else {
		/*
		 * We re-used an existing hierarchy - the new root (if
		 * any) is not needed
		 */
		cgroup_drop_root(opts.new_root);
	}

	simple_set_mnt(mnt, sb);
	kfree(opts.release_agent);
	kfree(opts.name);
	return 0;

 drop_new_super:
	deactivate_locked_super(sb);
 out_err:
	kfree(opts.release_agent);
	kfree(opts.name);

	return ret;
}

static void cgroup_kill_sb(struct super_block *sb) {
	struct cgroupfs_root *root = sb->s_fs_info;
	struct cgroup *cgrp = &root->top_cgroup;
	int ret;
	struct cg_cgroup_link *link;
	struct cg_cgroup_link *saved_link;

	BUG_ON(!root);

	BUG_ON(root->number_of_cgroups != 1);
	BUG_ON(!list_empty(&cgrp->children));
	BUG_ON(!list_empty(&cgrp->sibling));

	mutex_lock(&cgroup_mutex);

	/* Rebind all subsystems back to the default hierarchy */
	ret = rebind_subsystems(root, 0);
	/* Shouldn't be able to fail ... */
	BUG_ON(ret);

	/*
	 * Release all the links from css_sets to this hierarchy's
	 * root cgroup
	 */
	write_lock(&css_set_lock);

	list_for_each_entry_safe(link, saved_link, &cgrp->css_sets,
				 cgrp_link_list) {
		list_del(&link->cg_link_list);
		list_del(&link->cgrp_link_list);
		kfree(link);
	}
	write_unlock(&css_set_lock);

	if (!list_empty(&root->root_list)) {
		list_del(&root->root_list);
		root_count--;
	}

	mutex_unlock(&cgroup_mutex);

	kill_litter_super(sb);
	cgroup_drop_root(root);
}

static struct file_system_type cgroup_fs_type = {
	.name = "cgroup",
	.get_sb = cgroup_get_sb,
	.kill_sb = cgroup_kill_sb,
};

static inline struct cgroup *__d_cgrp(struct dentry *dentry)
{
	return dentry->d_fsdata;
}

static inline struct cftype *__d_cft(struct dentry *dentry)
{
	return dentry->d_fsdata;
}

/**
 * cgroup_path - generate the path of a cgroup
 * @cgrp: the cgroup in question
 * @buf: the buffer to write the path into
 * @buflen: the length of the buffer
 *
 * Called with cgroup_mutex held or else with an RCU-protected cgroup
 * reference.  Writes path of cgroup into buf.  Returns 0 on success,
 * -errno on error.
 */
int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
{
	char *start;
	struct dentry *dentry = rcu_dereference(cgrp->dentry);

	if (!dentry || cgrp == dummytop) {
		/*
		 * Inactive subsystems have no dentry for their root
		 * cgroup
		 */
		strcpy(buf, "/");
		return 0;
	}

	start = buf + buflen;

	*--start = '\0';
	for (;;) {
		int len = dentry->d_name.len;
		if ((start -= len) < buf)
			return -ENAMETOOLONG;
		memcpy(start, cgrp->dentry->d_name.name, len);
		cgrp = cgrp->parent;
		if (!cgrp)
			break;
		dentry = rcu_dereference(cgrp->dentry);
		if (!cgrp->parent)
			continue;
		if (--start < buf)
			return -ENAMETOOLONG;
		*start = '/';
	}
	memmove(buf, start, buf + buflen - start);
	return 0;
}

/**
 * cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
 * @cgrp: the cgroup the task is attaching to
 * @tsk: the task to be attached
 *
 * Call holding cgroup_mutex. May take task_lock of
 * the task 'tsk' during call.
 */
int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
	int retval = 0;
	struct cgroup_subsys *ss;
	struct cgroup *oldcgrp;
	struct css_set *cg;
	struct css_set *newcg;
	struct cgroupfs_root *root = cgrp->root;

	/* Nothing to do if the task is already in that cgroup */
	oldcgrp = task_cgroup_from_root(tsk, root);
	if (cgrp == oldcgrp)
		return 0;

	for_each_subsys(root, ss) {
		if (ss->can_attach) {
			retval = ss->can_attach(ss, cgrp, tsk);
			if (retval)
				return retval;
		}
	}

	task_lock(tsk);
	cg = tsk->cgroups;
	get_css_set(cg);
	task_unlock(tsk);
	/*
	 * Locate or allocate a new css_set for this task,
	 * based on its final set of cgroups
	 */
	newcg = find_css_set(cg, cgrp);
	put_css_set(cg);
	if (!newcg)
		return -ENOMEM;

	task_lock(tsk);
	if (tsk->flags & PF_EXITING) {
		task_unlock(tsk);
		put_css_set(newcg);
		return -ESRCH;
	}
	rcu_assign_pointer(tsk->cgroups, newcg);
	task_unlock(tsk);

	/* Update the css_set linked lists if we're using them */
	write_lock(&css_set_lock);
	if (!list_empty(&tsk->cg_list)) {
		list_del(&tsk->cg_list);
		list_add(&tsk->cg_list, &newcg->tasks);
	}
	write_unlock(&css_set_lock);

	for_each_subsys(root, ss) {
		if (ss->attach)
			ss->attach(ss, cgrp, oldcgrp, tsk);
	}
	set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
	synchronize_rcu();
	put_css_set(cg);

	/*
	 * wake up rmdir() waiter. the rmdir should fail since the cgroup
	 * is no longer empty.
	 */
	cgroup_wakeup_rmdir_waiter(cgrp);
	return 0;
}

/*
 * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
 * held. May take task_lock of task
 */
static int attach_task_by_pid(struct cgroup *cgrp, u64 pid)
{
	struct task_struct *tsk;
	const struct cred *cred = current_cred(), *tcred;
	int ret;

	if (pid) {
		rcu_read_lock();
		tsk = find_task_by_vpid(pid);
		if (!tsk || tsk->flags & PF_EXITING) {
			rcu_read_unlock();
			return -ESRCH;
		}

		tcred = __task_cred(tsk);
		if (cred->euid &&
		    cred->euid != tcred->uid &&
		    cred->euid != tcred->suid) {
			rcu_read_unlock();
			return -EACCES;
		}
		get_task_struct(tsk);
		rcu_read_unlock();
	} else {
		tsk = current;
		get_task_struct(tsk);
	}

	ret = cgroup_attach_task(cgrp, tsk);
	put_task_struct(tsk);
	return ret;
}

static int cgroup_tasks_write(struct cgroup *cgrp, struct cftype *cft, u64 pid)
{
	int ret;
	if (!cgroup_lock_live_group(cgrp))
		return -ENODEV;
	ret = attach_task_by_pid(cgrp, pid);
	cgroup_unlock();
	return ret;
}

/**
 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
 * @cgrp: the cgroup to be checked for liveness
 *
 * On success, returns true; the lock should be later released with
 * cgroup_unlock(). On failure returns false with no lock held.
 */
bool cgroup_lock_live_group(struct cgroup *cgrp)
{
	mutex_lock(&cgroup_mutex);
	if (cgroup_is_removed(cgrp)) {
		mutex_unlock(&cgroup_mutex);
		return false;
	}
	return true;
}

static int cgroup_release_agent_write(struct cgroup *cgrp, struct cftype *cft,
				      const char *buffer)
{
	BUILD_BUG_ON(sizeof(cgrp->root->release_agent_path) < PATH_MAX);
	if (!cgroup_lock_live_group(cgrp))
		return -ENODEV;
	strcpy(cgrp->root->release_agent_path, buffer);
	cgroup_unlock();
	return 0;
}

static int cgroup_release_agent_show(struct cgroup *cgrp, struct cftype *cft,
				     struct seq_file *seq)
{
	if (!cgroup_lock_live_group(cgrp))
		return -ENODEV;
	seq_puts(seq, cgrp->root->release_agent_path);
	seq_putc(seq, '\n');
	cgroup_unlock();
	return 0;
}

/* A buffer size big enough for numbers or short strings */
#define CGROUP_LOCAL_BUFFER_SIZE 64

static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
				struct file *file,
				const char __user *userbuf,
				size_t nbytes, loff_t *unused_ppos)
{
	char buffer[CGROUP_LOCAL_BUFFER_SIZE];
	int retval = 0;
	char *end;

	if (!nbytes)
		return -EINVAL;
	if (nbytes >= sizeof(buffer))
		return -E2BIG;
	if (copy_from_user(buffer, userbuf, nbytes))
		return -EFAULT;

	buffer[nbytes] = 0;     /* nul-terminate */
	strstrip(buffer);
	if (cft->write_u64) {
		u64 val = simple_strtoull(buffer, &end, 0);
		if (*end)
			return -EINVAL;
		retval = cft->write_u64(cgrp, cft, val);
	} else {
		s64 val = simple_strtoll(buffer, &end, 0);
		if (*end)
			return -EINVAL;
		retval = cft->write_s64(cgrp, cft, val);
	}
	if (!retval)
		retval = nbytes;
	return retval;
}

static ssize_t cgroup_write_string(struct cgroup *cgrp, struct cftype *cft,
				   struct file *file,
				   const char __user *userbuf,
				   size_t nbytes, loff_t *unused_ppos)
{
	char local_buffer[CGROUP_LOCAL_BUFFER_SIZE];
	int retval = 0;
	size_t max_bytes = cft->max_write_len;
	char *buffer = local_buffer;

	if (!max_bytes)
		max_bytes = sizeof(local_buffer) - 1;
	if (nbytes >= max_bytes)
		return -E2BIG;
	/* Allocate a dynamic buffer if we need one */
	if (nbytes >= sizeof(local_buffer)) {
		buffer = kmalloc(nbytes + 1, GFP_KERNEL);
		if (buffer == NULL)
			return -ENOMEM;
	}
	if (nbytes && copy_from_user(buffer, userbuf, nbytes)) {
		retval = -EFAULT;
		goto out;
	}

	buffer[nbytes] = 0;     /* nul-terminate */
	strstrip(buffer);
	retval = cft->write_string(cgrp, cft, buffer);
	if (!retval)
		retval = nbytes;
out:
	if (buffer != local_buffer)
		kfree(buffer);
	return retval;
}

static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
						size_t nbytes, loff_t *ppos)
{
	struct cftype *cft = __d_cft(file->f_dentry);
	struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);

	if (cgroup_is_removed(cgrp))
		return -ENODEV;
	if (cft->write)
		return cft->write(cgrp, cft, file, buf, nbytes, ppos);
	if (cft->write_u64 || cft->write_s64)
		return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
	if (cft->write_string)
		return cgroup_write_string(cgrp, cft, file, buf, nbytes, ppos);
	if (cft->trigger) {
		int ret = cft->trigger(cgrp, (unsigned int)cft->private);
		return ret ? ret : nbytes;
	}
	return -EINVAL;
}

static ssize_t cgroup_read_u64(struct cgroup *cgrp, struct cftype *cft,
			       struct file *file,
			       char __user *buf, size_t nbytes,
			       loff_t *ppos)
{
	char tmp[CGROUP_LOCAL_BUFFER_SIZE];
	u64 val = cft->read_u64(cgrp, cft);
	int len = sprintf(tmp, "%llu\n", (unsigned long long) val);

	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}

static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
			       struct file *file,
			       char __user *buf, size_t nbytes,
			       loff_t *ppos)
{
	char tmp[CGROUP_LOCAL_BUFFER_SIZE];
	s64 val = cft->read_s64(cgrp, cft);
	int len = sprintf(tmp, "%lld\n", (long long) val);

	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}

static ssize_t cgroup_file_read(struct file *file, char __user *buf,
				   size_t nbytes, loff_t *ppos)
{
	struct cftype *cft = __d_cft(file->f_dentry);
	struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);

	if (cgroup_is_removed(cgrp))
		return -ENODEV;

	if (cft->read)
		return cft->read(cgrp, cft, file, buf, nbytes, ppos);
	if (cft->read_u64)
		return cgroup_read_u64(cgrp, cft, file, buf, nbytes, ppos);
	if (cft->read_s64)
		return cgroup_read_s64(cgrp, cft, file, buf, nbytes, ppos);
	return -EINVAL;
}

/*
 * seqfile ops/methods for returning structured data. Currently just
 * supports string->u64 maps, but can be extended in future.
 */

struct cgroup_seqfile_state {
	struct cftype *cft;
	struct cgroup *cgroup;
};

static int cgroup_map_add(struct cgroup_map_cb *cb, const char *key, u64 value)
{
	struct seq_file *sf = cb->state;
	return seq_printf(sf, "%s %llu\n", key, (unsigned long long)value);
}

static int cgroup_seqfile_show(struct seq_file *m, void *arg)
{
	struct cgroup_seqfile_state *state = m->private;
	struct cftype *cft = state->cft;
	if (cft->read_map) {
		struct cgroup_map_cb cb = {
			.fill = cgroup_map_add,
			.state = m,
		};
		return cft->read_map(state->cgroup, cft, &cb);
	}
	return cft->read_seq_string(state->cgroup, cft, m);
}

static int cgroup_seqfile_release(struct inode *inode, struct file *file)
{
	struct seq_file *seq = file->private_data;
	kfree(seq->private);
	return single_release(inode, file);
}

static struct file_operations cgroup_seqfile_operations = {
	.read = seq_read,
	.write = cgroup_file_write,
	.llseek = seq_lseek,
	.release = cgroup_seqfile_release,
};

static int cgroup_file_open(struct inode *inode, struct file *file)
{
	int err;
	struct cftype *cft;

	err = generic_file_open(inode, file);
	if (err)
		return err;
	cft = __d_cft(file->f_dentry);

	if (cft->read_map || cft->read_seq_string) {
		struct cgroup_seqfile_state *state =
			kzalloc(sizeof(*state), GFP_USER);
		if (!state)
			return -ENOMEM;
		state->cft = cft;
		state->cgroup = __d_cgrp(file->f_dentry->d_parent);
		file->f_op = &cgroup_seqfile_operations;
		err = single_open(file, cgroup_seqfile_show, state);
		if (err < 0)
			kfree(state);
	} else if (cft->open)
		err = cft->open(inode, file);
	else
		err = 0;

	return err;
}

static int cgroup_file_release(struct inode *inode, struct file *file)
{
	struct cftype *cft = __d_cft(file->f_dentry);
	if (cft->release)
		return cft->release(inode, file);
	return 0;
}

/*
 * cgroup_rename - Only allow simple rename of directories in place.
 */
static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
			    struct inode *new_dir, struct dentry *new_dentry)
{
	if (!S_ISDIR(old_dentry->d_inode->i_mode))
		return -ENOTDIR;
	if (new_dentry->d_inode)
		return -EEXIST;
	if (old_dir != new_dir)
		return -EIO;
	return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
}

static struct file_operations cgroup_file_operations = {
	.read = cgroup_file_read,
	.write = cgroup_file_write,
	.llseek = generic_file_llseek,
	.open = cgroup_file_open,
	.release = cgroup_file_release,
};

static const struct inode_operations cgroup_dir_inode_operations = {
	.lookup = simple_lookup,
	.mkdir = cgroup_mkdir,
	.rmdir = cgroup_rmdir,
	.rename = cgroup_rename,
};

static int cgroup_create_file(struct dentry *dentry, mode_t mode,
				struct super_block *sb)
{
	static const struct dentry_operations cgroup_dops = {
		.d_iput = cgroup_diput,
	};

	struct inode *inode;

	if (!dentry)
		return -ENOENT;
	if (dentry->d_inode)
		return -EEXIST;

	inode = cgroup_new_inode(mode, sb);
	if (!inode)
		return -ENOMEM;

	if (S_ISDIR(mode)) {
		inode->i_op = &cgroup_dir_inode_operations;
		inode->i_fop = &simple_dir_operations;

		/* start off with i_nlink == 2 (for "." entry) */
		inc_nlink(inode);

		/* start with the directory inode held, so that we can
		 * populate it without racing with another mkdir */
		mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
	} else if (S_ISREG(mode)) {
		inode->i_size = 0;
		inode->i_fop = &cgroup_file_operations;
	}
	dentry->d_op = &cgroup_dops;
	d_instantiate(dentry, inode);
	dget(dentry);	/* Extra count - pin the dentry in core */
	return 0;
}

/*
 * cgroup_create_dir - create a directory for an object.
 * @cgrp: the cgroup we create the directory for. It must have a valid
 *        ->parent field. And we are going to fill its ->dentry field.
 * @dentry: dentry of the new cgroup
 * @mode: mode to set on new directory.
 */
static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
				mode_t mode)
{
	struct dentry *parent;
	int error = 0;

	parent = cgrp->parent->dentry;
	error = cgroup_create_file(dentry, S_IFDIR | mode, cgrp->root->sb);
	if (!error) {
		dentry->d_fsdata = cgrp;
		inc_nlink(parent->d_inode);
		rcu_assign_pointer(cgrp->dentry, dentry);
		dget(dentry);
	}
	dput(dentry);

	return error;
}

/**
 * cgroup_file_mode - deduce file mode of a control file
 * @cft: the control file in question
 *
 * returns cft->mode if ->mode is not 0
 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler
 * returns S_IRUGO if it has only a read handler
 * returns S_IWUSR if it has only a write hander
 */
static mode_t cgroup_file_mode(const struct cftype *cft)