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 */