include/linux/journal-head.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * include/linux/journal-head.h
   4  *
   5  * buffer_head fields for JBD
   6  *
   7  * 27 May 2001 Andrew Morton
   8  *      Created - pulled out of fs.h
   9  */
  10
  11 #ifndef JOURNAL_HEAD_H_INCLUDED
  12 #define JOURNAL_HEAD_H_INCLUDED
  13
  14 typedef unsigned int            tid_t;          /* Unique transaction ID */
  15 typedef struct transaction_s    transaction_t;  /* Compound transaction type */
  16
  17
  18 struct buffer_head;
  19
  20 struct journal_head {
  21         /*
  22          * Points back to our buffer_head. [jbd_lock_bh_journal_head()]
  23          */
  24         struct buffer_head *b_bh;
  25
  26         /*
  27          * Reference count - see description in journal.c
  28          * [jbd_lock_bh_journal_head()]
  29          */
  30         int b_jcount;
  31
  32         /*
  33          * Journalling list for this buffer [jbd_lock_bh_state()]
  34          * NOTE: We *cannot* combine this with b_modified into a bitfield
  35          * as gcc would then (which the C standard allows but which is
  36          * very unuseful) make 64-bit accesses to the bitfield and clobber
  37          * b_jcount if its update races with bitfield modification.
  38          */
  39         unsigned b_jlist;
  40
  41         /*
  42          * This flag signals the buffer has been modified by
  43          * the currently running transaction
  44          * [jbd_lock_bh_state()]
  45          */
  46         unsigned b_modified;
  47
  48         /*
  49          * Copy of the buffer data frozen for writing to the log.
  50          * [jbd_lock_bh_state()]
  51          */
  52         char *b_frozen_data;
  53
  54         /*
  55          * Pointer to a saved copy of the buffer containing no uncommitted
  56          * deallocation references, so that allocations can avoid overwriting
  57          * uncommitted deletes. [jbd_lock_bh_state()]
  58          */
  59         char *b_committed_data;
  60
  61         /*
  62          * Pointer to the compound transaction which owns this buffer's
  63          * metadata: either the running transaction or the committing
  64          * transaction (if there is one).  Only applies to buffers on a
  65          * transaction's data or metadata journaling list.
  66          * [j_list_lock] [jbd_lock_bh_state()]
  67          * Either of these locks is enough for reading, both are needed for
  68          * changes.
  69          */
  70         transaction_t *b_transaction;
  71
  72         /*
  73          * Pointer to the running compound transaction which is currently
  74          * modifying the buffer's metadata, if there was already a transaction
  75          * committing it when the new transaction touched it.
  76          * [t_list_lock] [jbd_lock_bh_state()]
  77          */
  78         transaction_t *b_next_transaction;
  79
  80         /*
  81          * Doubly-linked list of buffers on a transaction's data, metadata or
  82          * forget queue. [t_list_lock] [jbd_lock_bh_state()]
  83          */
  84         struct journal_head *b_tnext, *b_tprev;
  85
  86         /*
  87          * Pointer to the compound transaction against which this buffer
  88          * is checkpointed.  Only dirty buffers can be checkpointed.
  89          * [j_list_lock]
  90          */
  91         transaction_t *b_cp_transaction;
  92
  93         /*
  94          * Doubly-linked list of buffers still remaining to be flushed
  95          * before an old transaction can be checkpointed.
  96          * [j_list_lock]
  97          */
  98         struct journal_head *b_cpnext, *b_cpprev;
  99
 100         /* Trigger type */
 101         struct jbd2_buffer_trigger_type *b_triggers;
 102
 103         /* Trigger type for the committing transaction's frozen data */
 104         struct jbd2_buffer_trigger_type *b_frozen_triggers;
 105 };
 106
 107 #endif          /* JOURNAL_HEAD_H_INCLUDED */