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 #include <linux/spinlock.h>
  15
  16 typedef unsigned int            tid_t;          /* Unique transaction ID */
  17 typedef struct transaction_s    transaction_t;  /* Compound transaction type */
  18
  19
  20 struct buffer_head;
  21
  22 struct journal_head {
  23         /*
  24          * Points back to our buffer_head. [jbd_lock_bh_journal_head()]
  25          */
  26         struct buffer_head *b_bh;
  27
  28         /*
  29          * Protect the buffer head state
  30          */
  31         spinlock_t b_state_lock;
  32
  33         /*
  34          * Reference count - see description in journal.c
  35          * [jbd_lock_bh_journal_head()]
  36          */
  37         int b_jcount;
  38
  39         /*
  40          * Journalling list for this buffer [b_state_lock]
  41          * NOTE: We *cannot* combine this with b_modified into a bitfield
  42          * as gcc would then (which the C standard allows but which is
  43          * very unuseful) make 64-bit accesses to the bitfield and clobber
  44          * b_jcount if its update races with bitfield modification.
  45          */
  46         unsigned b_jlist;
  47
  48         /*
  49          * This flag signals the buffer has been modified by
  50          * the currently running transaction
  51          * [b_state_lock]
  52          */
  53         unsigned b_modified;
  54
  55         /*
  56          * Copy of the buffer data frozen for writing to the log.
  57          * [b_state_lock]
  58          */
  59         char *b_frozen_data;
  60
  61         /*
  62          * Pointer to a saved copy of the buffer containing no uncommitted
  63          * deallocation references, so that allocations can avoid overwriting
  64          * uncommitted deletes. [b_state_lock]
  65          */
  66         char *b_committed_data;
  67
  68         /*
  69          * Pointer to the compound transaction which owns this buffer's
  70          * metadata: either the running transaction or the committing
  71          * transaction (if there is one).  Only applies to buffers on a
  72          * transaction's data or metadata journaling list.
  73          * [j_list_lock] [b_state_lock]
  74          * Either of these locks is enough for reading, both are needed for
  75          * changes.
  76          */
  77         transaction_t *b_transaction;
  78
  79         /*
  80          * Pointer to the running compound transaction which is currently
  81          * modifying the buffer's metadata, if there was already a transaction
  82          * committing it when the new transaction touched it.
  83          * [t_list_lock] [b_state_lock]
  84          */
  85         transaction_t *b_next_transaction;
  86
  87         /*
  88          * Doubly-linked list of buffers on a transaction's data, metadata or
  89          * forget queue. [t_list_lock] [b_state_lock]
  90          */
  91         struct journal_head *b_tnext, *b_tprev;
  92
  93         /*
  94          * Pointer to the compound transaction against which this buffer
  95          * is checkpointed.  Only dirty buffers can be checkpointed.
  96          * [j_list_lock]
  97          */
  98         transaction_t *b_cp_transaction;
  99
 100         /*
 101          * Doubly-linked list of buffers still remaining to be flushed
 102          * before an old transaction can be checkpointed.
 103          * [j_list_lock]
 104          */
 105         struct journal_head *b_cpnext, *b_cpprev;
 106
 107         /* Trigger type */
 108         struct jbd2_buffer_trigger_type *b_triggers;
 109
 110         /* Trigger type for the committing transaction's frozen data */
 111         struct jbd2_buffer_trigger_type *b_frozen_triggers;
 112 };
 113
 114 #endif          /* JOURNAL_HEAD_H_INCLUDED */