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) Make all changes for the transaction *except* for the superblock.
42  * Then call dm_tm_pre_commit() to flush them to disk.
43  *
44  * ii) Lock your superblock.  Update.  Then call dm_tm_commit() which will
45  * unlock the superblock and flush it.  No other blocks should be updated
46  * during this period.  Care should be taken to never unlock a partially
47  * updated superblock; perform any operations that could fail *before* you
48  * take the superblock lock.
49  */
50 int dm_tm_pre_commit(struct dm_transaction_manager *tm);
51 int dm_tm_commit(struct dm_transaction_manager *tm, struct dm_block *superblock);
52 
53 /*
54  * These methods are the only way to get hold of a writeable block.
55  */
56 
57 /*
58  * dm_tm_new_block() is pretty self-explanatory.  Make sure you do actually
59  * write to the whole of @data before you unlock, otherwise you could get
60  * a data leak.  (The other option is for tm_new_block() to zero new blocks
61  * before handing them out, which will be redundant in most, if not all,
62  * cases).
63  * Zeroes the new block and returns with write lock held.
64  */
65 int dm_tm_new_block(struct dm_transaction_manager *tm,
66 		    struct dm_block_validator *v,
67 		    struct dm_block **result);
68 
69 /*
70  * dm_tm_shadow_block() allocates a new block and copies the data from @orig
71  * to it.  It then decrements the reference count on original block.  Use
72  * this to update the contents of a block in a data structure, don't
73  * confuse this with a clone - you shouldn't access the orig block after
74  * this operation.  Because the tm knows the scope of the transaction it
75  * can optimise requests for a shadow of a shadow to a no-op.  Don't forget
76  * to unlock when you've finished with the shadow.
77  *
78  * The @inc_children flag is used to tell the caller whether it needs to
79  * adjust reference counts for children.  (Data in the block may refer to
80  * other blocks.)
81  *
82  * Shadowing implicitly drops a reference on @orig so you must not have
83  * it locked when you call this.
84  */
85 int dm_tm_shadow_block(struct dm_transaction_manager *tm, dm_block_t orig,
86 		       struct dm_block_validator *v,
87 		       struct dm_block **result, int *inc_children);
88 
89 /*
90  * Read access.  You can lock any block you want.  If there's a write lock
91  * on it outstanding then it'll block.
92  */
93 int dm_tm_read_lock(struct dm_transaction_manager *tm, dm_block_t b,
94 		    struct dm_block_validator *v,
95 		    struct dm_block **result);
96 
97 void dm_tm_unlock(struct dm_transaction_manager *tm, struct dm_block *b);
98 
99 /*
100  * Functions for altering the reference count of a block directly.
101  */
102 void dm_tm_inc(struct dm_transaction_manager *tm, dm_block_t b);
103 
104 void dm_tm_dec(struct dm_transaction_manager *tm, dm_block_t b);
105 
106 int dm_tm_ref(struct dm_transaction_manager *tm, dm_block_t b,
107 	      uint32_t *result);
108 
109 struct dm_block_manager *dm_tm_get_bm(struct dm_transaction_manager *tm);
110 
111 /*
112  * If you're using a non-blocking clone the tm will build up a list of
113  * requested blocks that weren't in core.  This call will request those
114  * blocks to be prefetched.
115  */
116 void dm_tm_issue_prefetches(struct dm_transaction_manager *tm);
117 
118 /*
119  * A little utility that ties the knot by producing a transaction manager
120  * that has a space map managed by the transaction manager...
121  *
122  * Returns a tm that has an open transaction to write the new disk sm.
123  * Caller should store the new sm root and commit.
124  *
125  * The superblock location is passed so the metadata space map knows it
126  * shouldn't be used.
127  */
128 int dm_tm_create_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
129 			 struct dm_transaction_manager **tm,
130 			 struct dm_space_map **sm);
131 
132 int dm_tm_open_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
133 		       void *sm_root, size_t root_len,
134 		       struct dm_transaction_manager **tm,
135 		       struct dm_space_map **sm);
136 
137 #endif	/* _LINUX_DM_TRANSACTION_MANAGER_H */
138