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3241b1d3e0
The persistent-data library offers a re-usable framework for the storage and management of on-disk metadata in device-mapper targets. It's used by the thin-provisioning target in the next patch and in an upcoming hierarchical storage target. For further information, please read Documentation/device-mapper/persistent-data.txt Signed-off-by: Joe Thornber <thornber@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
131 lines
4.9 KiB
C
131 lines
4.9 KiB
C
/*
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* Copyright (C) 2011 Red Hat, Inc.
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*
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* This file is released under the GPL.
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*/
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#ifndef _LINUX_DM_TRANSACTION_MANAGER_H
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#define _LINUX_DM_TRANSACTION_MANAGER_H
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#include "dm-block-manager.h"
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struct dm_transaction_manager;
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struct dm_space_map;
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/*----------------------------------------------------------------*/
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/*
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* This manages the scope of a transaction. It also enforces immutability
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* of the on-disk data structures by limiting access to writeable blocks.
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*
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* Clients should not fiddle with the block manager directly.
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*/
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void dm_tm_destroy(struct dm_transaction_manager *tm);
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/*
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* The non-blocking version of a transaction manager is intended for use in
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* fast path code that needs to do lookups e.g. a dm mapping function.
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* You create the non-blocking variant from a normal tm. The interface is
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* the same, except that most functions will just return -EWOULDBLOCK.
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* Methods that return void yet may block should not be called on a clone
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* viz. dm_tm_inc, dm_tm_dec. Call dm_tm_destroy() as you would with a normal
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* tm when you've finished with it. You may not destroy the original prior
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* to clones.
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*/
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struct dm_transaction_manager *dm_tm_create_non_blocking_clone(struct dm_transaction_manager *real);
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/*
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* We use a 2-phase commit here.
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*
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* i) In the first phase the block manager is told to start flushing, and
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* the changes to the space map are written to disk. You should interrogate
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* your particular space map to get detail of its root node etc. to be
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* included in your superblock.
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*
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* ii) @root will be committed last. You shouldn't use more than the
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* first 512 bytes of @root if you wish the transaction to survive a power
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* failure. You *must* have a write lock held on @root for both stage (i)
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* and (ii). The commit will drop the write lock.
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*/
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int dm_tm_pre_commit(struct dm_transaction_manager *tm);
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int dm_tm_commit(struct dm_transaction_manager *tm, struct dm_block *root);
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/*
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* These methods are the only way to get hold of a writeable block.
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*/
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/*
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* dm_tm_new_block() is pretty self-explanatory. Make sure you do actually
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* write to the whole of @data before you unlock, otherwise you could get
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* a data leak. (The other option is for tm_new_block() to zero new blocks
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* before handing them out, which will be redundant in most, if not all,
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* cases).
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* Zeroes the new block and returns with write lock held.
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*/
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int dm_tm_new_block(struct dm_transaction_manager *tm,
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struct dm_block_validator *v,
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struct dm_block **result);
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/*
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* dm_tm_shadow_block() allocates a new block and copies the data from @orig
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* to it. It then decrements the reference count on original block. Use
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* this to update the contents of a block in a data structure, don't
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* confuse this with a clone - you shouldn't access the orig block after
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* this operation. Because the tm knows the scope of the transaction it
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* can optimise requests for a shadow of a shadow to a no-op. Don't forget
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* to unlock when you've finished with the shadow.
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*
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* The @inc_children flag is used to tell the caller whether it needs to
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* adjust reference counts for children. (Data in the block may refer to
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* other blocks.)
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*
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* Shadowing implicitly drops a reference on @orig so you must not have
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* it locked when you call this.
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*/
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int dm_tm_shadow_block(struct dm_transaction_manager *tm, dm_block_t orig,
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struct dm_block_validator *v,
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struct dm_block **result, int *inc_children);
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/*
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* Read access. You can lock any block you want. If there's a write lock
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* on it outstanding then it'll block.
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*/
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int dm_tm_read_lock(struct dm_transaction_manager *tm, dm_block_t b,
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struct dm_block_validator *v,
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struct dm_block **result);
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int dm_tm_unlock(struct dm_transaction_manager *tm, struct dm_block *b);
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/*
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* Functions for altering the reference count of a block directly.
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*/
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void dm_tm_inc(struct dm_transaction_manager *tm, dm_block_t b);
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void dm_tm_dec(struct dm_transaction_manager *tm, dm_block_t b);
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int dm_tm_ref(struct dm_transaction_manager *tm, dm_block_t b,
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uint32_t *result);
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struct dm_block_manager *dm_tm_get_bm(struct dm_transaction_manager *tm);
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/*
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* A little utility that ties the knot by producing a transaction manager
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* that has a space map managed by the transaction manager...
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*
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* Returns a tm that has an open transaction to write the new disk sm.
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* Caller should store the new sm root and commit.
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*/
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int dm_tm_create_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
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struct dm_block_validator *sb_validator,
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struct dm_transaction_manager **tm,
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struct dm_space_map **sm, struct dm_block **sblock);
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int dm_tm_open_with_sm(struct dm_block_manager *bm, dm_block_t sb_location,
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struct dm_block_validator *sb_validator,
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size_t root_offset, size_t root_max_len,
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struct dm_transaction_manager **tm,
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struct dm_space_map **sm, struct dm_block **sblock);
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#endif /* _LINUX_DM_TRANSACTION_MANAGER_H */
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