Root/drivers/md/persistent-data/dm-transaction-manager.h

1/*
2 * Copyright (C) 2011 Red Hat, Inc.
3 *
4 * This file is released under the GPL.
5 */
6
7#ifndef _LINUX_DM_TRANSACTION_MANAGER_H
8#define _LINUX_DM_TRANSACTION_MANAGER_H
9
10#include "dm-block-manager.h"
11
12struct dm_transaction_manager;
13struct dm_space_map;
14
15/*----------------------------------------------------------------*/
16
17/*
18 * This manages the scope of a transaction. It also enforces immutability
19 * of the on-disk data structures by limiting access to writeable blocks.
20 *
21 * Clients should not fiddle with the block manager directly.
22 */
23
24void dm_tm_destroy(struct dm_transaction_manager *tm);
25
26/*
27 * The non-blocking version of a transaction manager is intended for use in
28 * fast path code that needs to do lookups e.g. a dm mapping function.
29 * You create the non-blocking variant from a normal tm. The interface is
30 * the same, except that most functions will just return -EWOULDBLOCK.
31 * Methods that return void yet may block should not be called on a clone
32 * viz. dm_tm_inc, dm_tm_dec. Call dm_tm_destroy() as you would with a normal
33 * tm when you've finished with it. You may not destroy the original prior
34 * to clones.
35 */
36struct dm_transaction_manager *dm_tm_create_non_blocking_clone(struct dm_transaction_manager *real);
37
38/*
39 * We use a 2-phase commit here.
40 *
41 * i) In the first phase the block manager is told to start flushing, and
42 * the changes to the space map are written to disk. You should interrogate
43 * your particular space map to get detail of its root node etc. to be
44 * included in your superblock.
45 *
46 * ii) @root will be committed last. You shouldn't use more than the
47 * first 512 bytes of @root if you wish the transaction to survive a power
48 * failure. You *must* have a write lock held on @root for both stage (i)
49 * and (ii). The commit will drop the write lock.
50 */
51int dm_tm_pre_commit(struct dm_transaction_manager *tm);
52int dm_tm_commit(struct dm_transaction_manager *tm, struct dm_block *root);
53
54/*
55 * These methods are the only way to get hold of a writeable block.
56 */
57
58/*
59 * dm_tm_new_block() is pretty self-explanatory. Make sure you do actually
60 * write to the whole of @data before you unlock, otherwise you could get
61 * a data leak. (The other option is for tm_new_block() to zero new blocks
62 * before handing them out, which will be redundant in most, if not all,
63 * cases).
64 * Zeroes the new block and returns with write lock held.
65 */
66int dm_tm_new_block(struct dm_transaction_manager *tm,
67            struct dm_block_validator *v,
68            struct dm_block **result);
69
70/*
71 * dm_tm_shadow_block() allocates a new block and copies the data from @orig
72 * to it. It then decrements the reference count on original block. Use
73 * this to update the contents of a block in a data structure, don't
74 * confuse this with a clone - you shouldn't access the orig block after
75 * this operation. Because the tm knows the scope of the transaction it
76 * can optimise requests for a shadow of a shadow to a no-op. Don't forget
77 * to unlock when you've finished with the shadow.
78 *
79 * The @inc_children flag is used to tell the caller whether it needs to
80 * adjust reference counts for children. (Data in the block may refer to
81 * other blocks.)
82 *
83 * Shadowing implicitly drops a reference on @orig so you must not have
84 * it locked when you call this.
85 */
86int dm_tm_shadow_block(struct dm_transaction_manager *tm, dm_block_t orig,
87               struct dm_block_validator *v,
88               struct dm_block **result, int *inc_children);
89
90/*
91 * Read access. You can lock any block you want. If there's a write lock
92 * on it outstanding then it'll block.
93 */
94int dm_tm_read_lock(struct dm_transaction_manager *tm, dm_block_t b,
95            struct dm_block_validator *v,
96            struct dm_block **result);
97
98int dm_tm_unlock(struct dm_transaction_manager *tm, struct dm_block *b);
99
100/*
101 * Functions for altering the reference count of a block directly.
102 */
103void dm_tm_inc(struct dm_transaction_manager *tm, dm_block_t b);
104
105void dm_tm_dec(struct dm_transaction_manager *tm, dm_block_t b);
106
107int dm_tm_ref(struct dm_transaction_manager *tm, dm_block_t b,
108          uint32_t *result);
109
110struct dm_block_manager *dm_tm_get_bm(struct dm_transaction_manager *tm);
111
112/*
113 * A little utility that ties the knot by producing a transaction manager
114 * that has a space map managed by the transaction manager...
115 *
116 * Returns a tm that has an open transaction to write the new disk sm.
117 * Caller should store the new sm root and commit.
118 *
119 * The superblock location is passed so the metadata space map knows it
120 * shouldn't be used.
121 */
122int dm_tm_create_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
123             struct dm_transaction_manager **tm,
124             struct dm_space_map **sm);
125
126int dm_tm_open_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
127               void *sm_root, size_t root_len,
128               struct dm_transaction_manager **tm,
129               struct dm_space_map **sm);
130
131#endif /* _LINUX_DM_TRANSACTION_MANAGER_H */
132

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