include/linux/journal-head.h

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