text: /*
   * include/linux/journal-head.h
   *
   * buffer_head fields for JBD
   *
   * 27 May 2001 Andrew Morton
   *	Created - pulled out of fs.h
   */
  
  #ifndef JOURNAL_HEAD_H_INCLUDED
  #define JOURNAL_HEAD_H_INCLUDED
  
  typedef unsigned int		tid_t;		/* Unique transaction ID */
  typedef struct transaction_s	transaction_t;	/* Compound transaction type */
  
  
  struct buffer_head;
  
  struct journal_head {
  	/*
  	 * Points back to our buffer_head. [jbd_lock_bh_journal_head()]
  	 */
  	struct buffer_head *b_bh;
  
  	/*
  	 * Reference count - see description in journal.c
  	 * [jbd_lock_bh_journal_head()]
  	 */
  	int b_jcount;
  
  	/*
  	 * Journalling list for this buffer [jbd_lock_bh_state()]
  	 */
  	unsigned b_jlist;
  
  	/*
  	 * This flag signals the buffer has been modified by
  	 * the currently running transaction
  	 * [jbd_lock_bh_state()]
  	 */
  	unsigned b_modified;
  
  	/*
  	 * This feild tracks the last transaction id in which this buffer
  	 * has been cowed
  	 * [jbd_lock_bh_state()]
  	 */
  	unsigned b_cow_tid;
  
  	/*
  	 * Copy of the buffer data frozen for writing to the log.
  	 * [jbd_lock_bh_state()]
  	 */
  	char *b_frozen_data;
  
  	/*
  	 * Pointer to a saved copy of the buffer containing no uncommitted
  	 * deallocation references, so that allocations can avoid overwriting
  	 * uncommitted deletes. [jbd_lock_bh_state()]
  	 */
  	char *b_committed_data;
  
  	/*
  	 * Pointer to the compound transaction which owns this buffer's
  	 * metadata: either the running transaction or the committing
  	 * transaction (if there is one).  Only applies to buffers on a
  	 * transaction's data or metadata journaling list.
  	 * [j_list_lock] [jbd_lock_bh_state()]
  	 */
  	transaction_t *b_transaction;
  
  	/*
  	 * Pointer to the running compound transaction which is currently
  	 * modifying the buffer's metadata, if there was already a transaction
  	 * committing it when the new transaction touched it.
  	 * [t_list_lock] [jbd_lock_bh_state()]
  	 */
  	transaction_t *b_next_transaction;
  
  	/*
  	 * Doubly-linked list of buffers on a transaction's data, metadata or
  	 * forget queue. [t_list_lock] [jbd_lock_bh_state()]
  	 */
  	struct journal_head *b_tnext, *b_tprev;
  
  	/*
  	 * Pointer to the compound transaction against which this buffer
  	 * is checkpointed.  Only dirty buffers can be checkpointed.
  	 * [j_list_lock]
  	 */
  	transaction_t *b_cp_transaction;
  
  	/*
  	 * Doubly-linked list of buffers still remaining to be flushed
  	 * before an old transaction can be checkpointed.
  	 * [j_list_lock]
  	 */
  	struct journal_head *b_cpnext, *b_cpprev;
  
  	/* Trigger type */
  	struct jbd2_buffer_trigger_type *b_triggers;
  
  	/* Trigger type for the committing transaction's frozen data */
  	struct jbd2_buffer_trigger_type *b_frozen_triggers;
  };
  
  #endif		/* JOURNAL_HEAD_H_INCLUDED */
  