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
  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 */