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 */
115