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 */
108