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) 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 int 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  * A little utility that ties the knot by producing a transaction manager
 113  * that has a space map managed by the transaction manager...
 114  *
 115  * Returns a tm that has an open transaction to write the new disk sm.
 116  * Caller should store the new sm root and commit.
 117  *
 118  * The superblock location is passed so the metadata space map knows it
 119  * shouldn't be used.
 120  */
 121 int dm_tm_create_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
 122                          struct dm_transaction_manager **tm,
 123                          struct dm_space_map **sm);
 124
 125 int dm_tm_open_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
 126                        void *sm_root, size_t root_len,
 127                        struct dm_transaction_manager **tm,
 128                        struct dm_space_map **sm);
 129
 130 #endif  /* _LINUX_DM_TRANSACTION_MANAGER_H */