journal-head.h

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/*
 * 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()]
     */
    tid_t 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()]
     * Either of these locks is enough for reading, both are needed for
     * changes.
     */
    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 */