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 	 */
34 	unsigned b_jlist;
35 
36 	/*
37 	 * This flag signals the buffer has been modified by
38 	 * the currently running transaction
39 	 * [jbd_lock_bh_state()]
40 	 */
41 	unsigned b_modified;
42 
43 	/*
44 	 * This feild tracks the last transaction id in which this buffer
45 	 * has been cowed
46 	 * [jbd_lock_bh_state()]
47 	 */
48 	tid_t b_cow_tid;
49 
50 	/*
51 	 * Copy of the buffer data frozen for writing to the log.
52 	 * [jbd_lock_bh_state()]
53 	 */
54 	char *b_frozen_data;
55 
56 	/*
57 	 * Pointer to a saved copy of the buffer containing no uncommitted
58 	 * deallocation references, so that allocations can avoid overwriting
59 	 * uncommitted deletes. [jbd_lock_bh_state()]
60 	 */
61 	char *b_committed_data;
62 
63 	/*
64 	 * Pointer to the compound transaction which owns this buffer's
65 	 * metadata: either the running transaction or the committing
66 	 * transaction (if there is one).  Only applies to buffers on a
67 	 * transaction's data or metadata journaling list.
68 	 * [j_list_lock] [jbd_lock_bh_state()]
69 	 * Either of these locks is enough for reading, both are needed for
70 	 * changes.
71 	 */
72 	transaction_t *b_transaction;
73 
74 	/*
75 	 * Pointer to the running compound transaction which is currently
76 	 * modifying the buffer's metadata, if there was already a transaction
77 	 * committing it when the new transaction touched it.
78 	 * [t_list_lock] [jbd_lock_bh_state()]
79 	 */
80 	transaction_t *b_next_transaction;
81 
82 	/*
83 	 * Doubly-linked list of buffers on a transaction's data, metadata or
84 	 * forget queue. [t_list_lock] [jbd_lock_bh_state()]
85 	 */
86 	struct journal_head *b_tnext, *b_tprev;
87 
88 	/*
89 	 * Pointer to the compound transaction against which this buffer
90 	 * is checkpointed.  Only dirty buffers can be checkpointed.
91 	 * [j_list_lock]
92 	 */
93 	transaction_t *b_cp_transaction;
94 
95 	/*
96 	 * Doubly-linked list of buffers still remaining to be flushed
97 	 * before an old transaction can be checkpointed.
98 	 * [j_list_lock]
99 	 */
100 	struct journal_head *b_cpnext, *b_cpprev;
101 
102 	/* Trigger type */
103 	struct jbd2_buffer_trigger_type *b_triggers;
104 
105 	/* Trigger type for the committing transaction's frozen data */
106 	struct jbd2_buffer_trigger_type *b_frozen_triggers;
107 };
108 
109 #endif		/* JOURNAL_HEAD_H_INCLUDED */
110