#include <linux/proc_fs.h>
#include <linux/sched.h>
#include <linux/namei.h>

/*
 * /proc/self:
 */
static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
			      int buflen)
{
	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
	pid_t tgid = task_tgid_nr_ns(current, ns);
	char tmp[PROC_NUMBUF];
	if (!tgid)
		return -ENOENT;
	sprintf(tmp, "%d", tgid);
	return vfs_readlink(dentry,buffer,buflen,tmp);
}

static void *proc_self_follow_link(struct dentry *dentry, struct nameidata *nd)
{
	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
	pid_t tgid = task_tgid_nr_ns(current, ns);
	char *name = ERR_PTR(-ENOENT);
	if (tgid) {
		/* 11 for max length of signed int in decimal + NULL term */
		name = kmalloc(12, GFP_KERNEL);
		if (!name)
			name = ERR_PTR(-ENOMEM);
		else
			sprintf(name, "%d", tgid);
	}
	nd_set_link(nd, name);
	return NULL;
}

static void proc_self_put_link(struct dentry *dentry, struct nameidata *nd,
				void *cookie)
{
	char *s = nd_get_link(nd);
	if (!IS_ERR(s))
		kfree(s);
}

static const struct inode_operations proc_self_inode_operations = {
	.readlink	= proc_self_readlink,
	.follow_link	= proc_self_follow_link,
	.put_link	= proc_self_put_link,
};

void __init proc_self_init(void)
{
	struct proc_dir_entry *proc_self_symlink;
	mode_t mode;

	mode = S_IFLNK | S_IRWXUGO;
	proc_self_symlink = proc_create("self", mode, NULL, NULL );
	proc_self_symlink->proc_iops = &proc_self_inode_operations;
}