#include <linux/sched.h>
#include <linux/namei.h>
#include <linux/slab.h>
#include <linux/pid_namespace.h>
#include "internal.h"

/*
 * /proc/thread_self:
 */
static int proc_thread_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);
	pid_t pid = task_pid_nr_ns(current, ns);
	char tmp[PROC_NUMBUF + 6 + PROC_NUMBUF];
	if (!pid)
		return -ENOENT;
	sprintf(tmp, "%d/task/%d", tgid, pid);
	return readlink_copy(buffer, buflen, tmp);
}

static void *proc_thread_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);
	pid_t pid = task_pid_nr_ns(current, ns);
	char *name = ERR_PTR(-ENOENT);
	if (pid) {
		name = kmalloc(PROC_NUMBUF + 6 + PROC_NUMBUF, GFP_KERNEL);
		if (!name)
			name = ERR_PTR(-ENOMEM);
		else
			sprintf(name, "%d/task/%d", tgid, pid);
	}
	nd_set_link(nd, name);
	return NULL;
}

static const struct inode_operations proc_thread_self_inode_operations = {
	.readlink	= proc_thread_self_readlink,
	.follow_link	= proc_thread_self_follow_link,
	.put_link	= kfree_put_link,
};

static unsigned thread_self_inum;

int proc_setup_thread_self(struct super_block *s)
{
	struct inode *root_inode = s->s_root->d_inode;
	struct pid_namespace *ns = s->s_fs_info;
	struct dentry *thread_self;

	mutex_lock(&root_inode->i_mutex);
	thread_self = d_alloc_name(s->s_root, "thread-self");
	if (thread_self) {
		struct inode *inode = new_inode_pseudo(s);
		if (inode) {
			inode->i_ino = thread_self_inum;
			inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
			inode->i_mode = S_IFLNK | S_IRWXUGO;
			inode->i_uid = GLOBAL_ROOT_UID;
			inode->i_gid = GLOBAL_ROOT_GID;
			inode->i_op = &proc_thread_self_inode_operations;
			d_add(thread_self, inode);
		} else {
			dput(thread_self);
			thread_self = ERR_PTR(-ENOMEM);
		}
	} else {
		thread_self = ERR_PTR(-ENOMEM);
	}
	mutex_unlock(&root_inode->i_mutex);
	if (IS_ERR(thread_self)) {
		pr_err("proc_fill_super: can't allocate /proc/thread_self\n");
		return PTR_ERR(thread_self);
	}
	ns->proc_thread_self = thread_self;
	return 0;
}

void __init proc_thread_self_init(void)
{
	proc_alloc_inum(&thread_self_inum);
}