#ifndef _LINUX_PIPE_FS_I_H
  #define _LINUX_PIPE_FS_I_H
  
  #define PIPEFS_MAGIC 0x50495045

  #define PIPE_DEF_BUFFERS	16

  #define PIPE_BUF_FLAG_LRU	0x01	/* page is on the LRU */
  #define PIPE_BUF_FLAG_ATOMIC	0x02	/* was atomically mapped */
  #define PIPE_BUF_FLAG_GIFT	0x04	/* page is a gift */

  /**
   *	struct pipe_buffer - a linux kernel pipe buffer
   *	@page: the page containing the data for the pipe buffer
   *	@offset: offset of data inside the @page
   *	@len: length of data inside the @page
   *	@ops: operations associated with this buffer. See @pipe_buf_operations.
   *	@flags: pipe buffer flags. See above.
   *	@private: private data owned by the ops.
   **/

  struct pipe_buffer {
  	struct page *page;
  	unsigned int offset, len;

  	const struct pipe_buf_operations *ops;

  	unsigned int flags;

  	unsigned long private;

  };

  /**
   *	struct pipe_inode_info - a linux kernel pipe
   *	@wait: reader/writer wait point in case of empty/full pipe
   *	@nrbufs: the number of non-empty pipe buffers in this pipe

   *	@buffers: total number of buffers (should be a power of 2)

   *	@curbuf: the current pipe buffer entry
   *	@tmp_page: cached released page
   *	@readers: number of current readers of this pipe
   *	@writers: number of current writers of this pipe
   *	@waiting_writers: number of writers blocked waiting for room
   *	@r_counter: reader counter
   *	@w_counter: writer counter
   *	@fasync_readers: reader side fasync
   *	@fasync_writers: writer side fasync
   *	@inode: inode this pipe is attached to
   *	@bufs: the circular array of pipe buffers
   **/

  struct pipe_inode_info {
  	wait_queue_head_t wait;

  	unsigned int nrbufs, curbuf, buffers;

  	unsigned int readers;
  	unsigned int writers;
  	unsigned int waiting_writers;
  	unsigned int r_counter;
  	unsigned int w_counter;

  	struct page *tmp_page;

  	struct fasync_struct *fasync_readers;
  	struct fasync_struct *fasync_writers;
  	struct inode *inode;

  	struct pipe_buffer *bufs;

  };

  /*
   * Note on the nesting of these functions:
   *

   * ->confirm()

   *	->steal()
   *	...
   *	->map()
   *	...
   *	->unmap()
   *

   * That is, ->map() must be called on a confirmed buffer,

   * same goes for ->steal(). See below for the meaning of each
   * operation. Also see kerneldoc in fs/pipe.c for the pipe
   * and generic variants of these hooks.

   */

  struct pipe_buf_operations {

  	/*
  	 * This is set to 1, if the generic pipe read/write may coalesce
  	 * data into an existing buffer. If this is set to 0, a new pipe
  	 * page segment is always used for new data.
  	 */

  	int can_merge;

  
  	/*
  	 * ->map() returns a virtual address mapping of the pipe buffer.
  	 * The last integer flag reflects whether this should be an atomic
  	 * mapping or not. The atomic map is faster, however you can't take
  	 * page faults before calling ->unmap() again. So if you need to eg
  	 * access user data through copy_to/from_user(), then you must get
  	 * a non-atomic map. ->map() uses the KM_USER0 atomic slot for
  	 * atomic maps, so you can't map more than one pipe_buffer at once
  	 * and you have to be careful if mapping another page as source
  	 * or destination for a copy (IOW, it has to use something else
  	 * than KM_USER0).
  	 */

  	void * (*map)(struct pipe_inode_info *, struct pipe_buffer *, int);

  
  	/*
  	 * Undoes ->map(), finishes the virtual mapping of the pipe buffer.
  	 */

  	void (*unmap)(struct pipe_inode_info *, struct pipe_buffer *, void *);

  
  	/*
  	 * ->confirm() verifies that the data in the pipe buffer is there
  	 * and that the contents are good. If the pages in the pipe belong
  	 * to a file system, we may need to wait for IO completion in this
  	 * hook. Returns 0 for good, or a negative error value in case of
  	 * error.
  	 */

  	int (*confirm)(struct pipe_inode_info *, struct pipe_buffer *);

  
  	/*
  	 * When the contents of this pipe buffer has been completely
  	 * consumed by a reader, ->release() is called.
  	 */

  	void (*release)(struct pipe_inode_info *, struct pipe_buffer *);

  
  	/*
  	 * Attempt to take ownership of the pipe buffer and its contents.
  	 * ->steal() returns 0 for success, in which case the contents
  	 * of the pipe (the buf->page) is locked and now completely owned
  	 * by the caller. The page may then be transferred to a different
  	 * mapping, the most often used case is insertion into different
  	 * file address space cache.
  	 */

  	int (*steal)(struct pipe_inode_info *, struct pipe_buffer *);

  
  	/*
  	 * Get a reference to the pipe buffer.
  	 */

  	void (*get)(struct pipe_inode_info *, struct pipe_buffer *);

  };

  /* Differs from PIPE_BUF in that PIPE_SIZE is the length of the actual
     memory allocation, whereas PIPE_BUF makes atomicity guarantees.  */
  #define PIPE_SIZE		PAGE_SIZE

  /* Pipe lock and unlock operations */
  void pipe_lock(struct pipe_inode_info *);
  void pipe_unlock(struct pipe_inode_info *);
  void pipe_double_lock(struct pipe_inode_info *, struct pipe_inode_info *);

  extern unsigned int pipe_max_size, pipe_min_size;
  int pipe_proc_fn(struct ctl_table *, int, void __user *, size_t *, loff_t *);

  /* Drop the inode semaphore and wait for a pipe event, atomically */

  void pipe_wait(struct pipe_inode_info *pipe);

  struct pipe_inode_info * alloc_pipe_info(struct inode * inode);
  void free_pipe_info(struct inode * inode);

  void __free_pipe_info(struct pipe_inode_info *);

  /* Generic pipe buffer ops functions */

  void *generic_pipe_buf_map(struct pipe_inode_info *, struct pipe_buffer *, int);
  void generic_pipe_buf_unmap(struct pipe_inode_info *, struct pipe_buffer *, void *);

  void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);

  int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);

  int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);

  void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);

  /* for F_SETPIPE_SZ and F_GETPIPE_SZ */
  long pipe_fcntl(struct file *, unsigned int, unsigned long arg);

  struct pipe_inode_info *get_pipe_info(struct file *file);

  #endif