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dm-transaction-manager.h
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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 
12 struct dm_transaction_manager;
13 struct 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 
24 void 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  */
36 struct 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  */
51 int dm_tm_pre_commit(struct dm_transaction_manager *tm);
52 int 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  */
66 int 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  */
86 int 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  */
94 int 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 
98 int 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  */
103 void dm_tm_inc(struct dm_transaction_manager *tm, dm_block_t b);
104 
105 void dm_tm_dec(struct dm_transaction_manager *tm, dm_block_t b);
106 
107 int dm_tm_ref(struct dm_transaction_manager *tm, dm_block_t b,
108  uint32_t *result);
109 
110 struct 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  */
122 int 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 
126 int 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 */
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