text: // 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 = inode->i_sb->s_fs_info;
  	pid_t tgid = task_tgid_nr_ns(current, ns);
  	char *name;
  
  	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 pid_namespace *ns = s->s_fs_info;
  	struct dentry *self;
  	
  	inode_lock(root_inode);
  	self = d_alloc_name(s->s_root, "self");
  	if (self) {
  		struct inode *inode = new_inode_pseudo(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);
  		} else {
  			dput(self);
  			self = ERR_PTR(-ENOMEM);
  		}
  	} else {
  		self = ERR_PTR(-ENOMEM);
  	}
  	inode_unlock(root_inode);
  	if (IS_ERR(self)) {
  		pr_err("proc_fill_super: can't allocate /proc/self\n");
  		return PTR_ERR(self);
  	}
  	ns->proc_self = self;
  	return 0;
  }
  
  void __init proc_self_init(void)
  {
  	proc_alloc_inum(&self_inum);
  }
  