// SPDX-License-Identifier: GPL-2.0-only

  /*
   *  fs/anon_inodes.c
   *
   *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   *
   *  Thanks to Arnd Bergmann for code review and suggestions.
   *  More changes for Thomas Gleixner suggestions.
   *
   */

  #include <linux/cred.h>

  #include <linux/file.h>
  #include <linux/poll.h>

  #include <linux/sched.h>

  #include <linux/init.h>
  #include <linux/fs.h>
  #include <linux/mount.h>
  #include <linux/module.h>
  #include <linux/kernel.h>
  #include <linux/magic.h>
  #include <linux/anon_inodes.h>

  #include <linux/pseudo_fs.h>

  #include <linux/uaccess.h>

  
  static struct vfsmount *anon_inode_mnt __read_mostly;
  static struct inode *anon_inode_inode;

  /*
   * anon_inodefs_dname() is called from d_path().
   */
  static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen)
  {
  	return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s",
  				dentry->d_name.name);
  }

  static const struct dentry_operations anon_inodefs_dentry_operations = {
  	.d_dname	= anon_inodefs_dname,
  };

  static int anon_inodefs_init_fs_context(struct fs_context *fc)

  {

  	struct pseudo_fs_context *ctx = init_pseudo(fc, ANON_INODE_FS_MAGIC);
  	if (!ctx)
  		return -ENOMEM;
  	ctx->dops = &anon_inodefs_dentry_operations;
  	return 0;

  }
  
  static struct file_system_type anon_inode_fs_type = {
  	.name		= "anon_inodefs",

  	.init_fs_context = anon_inodefs_init_fs_context,

  	.kill_sb	= kill_anon_super,
  };

  /**

   * anon_inode_getfile - creates a new file instance by hooking it up to an
   *                      anonymous inode, and a dentry that describe the "class"
   *                      of the file

   *

   * @name:    [in]    name of the "class" of the new file

   * @fops:    [in]    file operations for the new file
   * @priv:    [in]    private data for the new file (will be file's private_data)
   * @flags:   [in]    flags

   *
   * Creates a new file by hooking it on a single inode. This is useful for files
   * that do not need to have a full-fledged inode in order to operate correctly.

   * All the files created with anon_inode_getfile() will share a single inode,

   * hence saving memory and avoiding code duplication for the file/inode/dentry

   * setup.  Returns the newly created file* or an error pointer.

   */

  struct file *anon_inode_getfile(const char *name,
  				const struct file_operations *fops,
  				void *priv, int flags)

  {

  	struct file *file;

  
  	if (IS_ERR(anon_inode_inode))

  		return ERR_PTR(-ENODEV);

  	if (fops->owner && !try_module_get(fops->owner))

  		return ERR_PTR(-ENOENT);

  
  	/*

  	 * We know the anon_inode inode count is always greater than zero,

  	 * so ihold() is safe.

  	 */

  	ihold(anon_inode_inode);

  	file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name,
  				 flags & (O_ACCMODE | O_NONBLOCK), fops);

  	if (IS_ERR(file))

  		goto err;

  	file->f_mapping = anon_inode_inode->i_mapping;

  	file->private_data = priv;

  	return file;

  err:
  	iput(anon_inode_inode);

  	module_put(fops->owner);

  	return file;

  }
  EXPORT_SYMBOL_GPL(anon_inode_getfile);
  
  /**
   * anon_inode_getfd - creates a new file instance by hooking it up to an
   *                    anonymous inode, and a dentry that describe the "class"
   *                    of the file
   *
   * @name:    [in]    name of the "class" of the new file
   * @fops:    [in]    file operations for the new file
   * @priv:    [in]    private data for the new file (will be file's private_data)
   * @flags:   [in]    flags
   *
   * Creates a new file by hooking it on a single inode. This is useful for files
   * that do not need to have a full-fledged inode in order to operate correctly.
   * All the files created with anon_inode_getfd() will share a single inode,
   * hence saving memory and avoiding code duplication for the file/inode/dentry
   * setup.  Returns new descriptor or an error code.
   */
  int anon_inode_getfd(const char *name, const struct file_operations *fops,
  		     void *priv, int flags)
  {
  	int error, fd;
  	struct file *file;
  
  	error = get_unused_fd_flags(flags);
  	if (error < 0)
  		return error;
  	fd = error;
  
  	file = anon_inode_getfile(name, fops, priv, flags);
  	if (IS_ERR(file)) {
  		error = PTR_ERR(file);
  		goto err_put_unused_fd;
  	}

  	fd_install(fd, file);

  	return fd;

  
  err_put_unused_fd:
  	put_unused_fd(fd);

  	return error;
  }

  EXPORT_SYMBOL_GPL(anon_inode_getfd);

  static int __init anon_inode_init(void)
  {

  	anon_inode_mnt = kern_mount(&anon_inode_fs_type);

  	if (IS_ERR(anon_inode_mnt))
  		panic("anon_inode_init() kernel mount failed (%ld)
  ", PTR_ERR(anon_inode_mnt));

  	anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb);
  	if (IS_ERR(anon_inode_inode))
  		panic("anon_inode_init() inode allocation failed (%ld)
  ", PTR_ERR(anon_inode_inode));
  
  	return 0;

  }
  
  fs_initcall(anon_inode_init);