// SPDX-License-Identifier: GPL-2.0

  #include <linux/cache.h>

  #include <linux/sched.h>

  #include <linux/slab.h>

  #include <linux/pid_namespace.h>
  #include "internal.h"

  
  /*
   * /proc/self:
   */

  static const char *proc_self_get_link(struct dentry *dentry,

  				      struct inode *inode,
  				      struct delayed_call *done)

  {

  	struct pid_namespace *ns = proc_pid_ns(inode->i_sb);

  	pid_t tgid = task_tgid_nr_ns(current, ns);

  	char *name;

  	/*
  	 * Not currently supported. Once we can inherit all of struct pid,
  	 * we can allow this.
  	 */
  	if (current->flags & PF_KTHREAD)
  		return ERR_PTR(-EOPNOTSUPP);

  	if (!tgid)
  		return ERR_PTR(-ENOENT);

  	/* max length of unsigned int in decimal + NULL term */
  	name = kmalloc(10 + 1, dentry ? GFP_KERNEL : GFP_ATOMIC);

  	if (unlikely(!name))
  		return dentry ? ERR_PTR(-ENOMEM) : ERR_PTR(-ECHILD);

  	sprintf(name, "%u", tgid);

  	set_delayed_call(done, kfree_link, name);
  	return name;

  }

  static const struct inode_operations proc_self_inode_operations = {

  	.get_link	= proc_self_get_link,

  };

  static unsigned self_inum __ro_after_init;

  
  int proc_setup_self(struct super_block *s)

  {

  	struct inode *root_inode = d_inode(s->s_root);

  	struct proc_fs_info *fs_info = proc_sb_info(s);

  	struct dentry *self;

  	int ret = -ENOMEM;

  	inode_lock(root_inode);

  	self = d_alloc_name(s->s_root, "self");
  	if (self) {

  		struct inode *inode = new_inode(s);

  		if (inode) {
  			inode->i_ino = self_inum;

  			inode->i_mtime = inode->i_atime = inode->i_ctime = current_time(inode);

  			inode->i_mode = S_IFLNK | S_IRWXUGO;
  			inode->i_uid = GLOBAL_ROOT_UID;
  			inode->i_gid = GLOBAL_ROOT_GID;
  			inode->i_op = &proc_self_inode_operations;
  			d_add(self, inode);

  			ret = 0;

  		} else {
  			dput(self);

  		}

  	}

  	inode_unlock(root_inode);

  
  	if (ret)

  		pr_err("proc_fill_super: can't allocate /proc/self
  ");

  	else

  		fs_info->proc_self = self;

  
  	return ret;

  }

  void __init proc_self_init(void)
  {
  	proc_alloc_inum(&self_inum);

  }