167 lines
5.6 KiB
C
167 lines
5.6 KiB
C
/*
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* Copyright (C) 2012 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_ARRAY_H
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#define _LINUX_DM_ARRAY_H
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#include "dm-btree.h"
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/*----------------------------------------------------------------*/
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/*
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* The dm-array is a persistent version of an array. It packs the data
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* more efficiently than a btree which will result in less disk space use,
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* and a performance boost. The element get and set operations are still
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* O(ln(n)), but with a much smaller constant.
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*
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* The value type structure is reused from the btree type to support proper
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* reference counting of values.
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*
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* The arrays implicitly know their length, and bounds are checked for
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* lookups and updated. It doesn't store this in an accessible place
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* because it would waste a whole metadata block. Make sure you store the
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* size along with the array root in your encompassing data.
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*
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* Array entries are indexed via an unsigned integer starting from zero.
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* Arrays are not sparse; if you resize an array to have 'n' entries then
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* 'n - 1' will be the last valid index.
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*
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* Typical use:
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*
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* a) initialise a dm_array_info structure. This describes the array
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* values and ties it into a specific transaction manager. It holds no
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* instance data; the same info can be used for many similar arrays if
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* you wish.
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*
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* b) Get yourself a root. The root is the index of a block of data on the
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* disk that holds a particular instance of an array. You may have a
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* pre existing root in your metadata that you wish to use, or you may
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* want to create a brand new, empty array with dm_array_empty().
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*
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* Like the other data structures in this library, dm_array objects are
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* immutable between transactions. Update functions will return you the
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* root for a _new_ array. If you've incremented the old root, via
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* dm_tm_inc(), before calling the update function you may continue to use
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* it in parallel with the new root.
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*
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* c) resize an array with dm_array_resize().
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*
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* d) Get a value from the array with dm_array_get_value().
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*
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* e) Set a value in the array with dm_array_set_value().
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*
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* f) Walk an array of values in index order with dm_array_walk(). More
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* efficient than making many calls to dm_array_get_value().
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*
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* g) Destroy the array with dm_array_del(). This tells the transaction
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* manager that you're no longer using this data structure so it can
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* recycle it's blocks. (dm_array_dec() would be a better name for it,
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* but del is in keeping with dm_btree_del()).
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*/
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/*
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* Describes an array. Don't initialise this structure yourself, use the
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* init function below.
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*/
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struct dm_array_info {
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struct dm_transaction_manager *tm;
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struct dm_btree_value_type value_type;
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struct dm_btree_info btree_info;
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};
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/*
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* Sets up a dm_array_info structure. You don't need to do anything with
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* this structure when you finish using it.
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*
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* info - the structure being filled in.
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* tm - the transaction manager that should supervise this structure.
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* vt - describes the leaf values.
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*/
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void dm_array_info_init(struct dm_array_info *info,
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struct dm_transaction_manager *tm,
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struct dm_btree_value_type *vt);
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/*
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* Create an empty, zero length array.
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*
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* info - describes the array
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* root - on success this will be filled out with the root block
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*/
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int dm_array_empty(struct dm_array_info *info, dm_block_t *root);
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/*
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* Resizes the array.
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*
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* info - describes the array
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* root - the root block of the array on disk
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* old_size - the caller is responsible for remembering the size of
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* the array
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* new_size - can be bigger or smaller than old_size
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* value - if we're growing the array the new entries will have this value
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* new_root - on success, points to the new root block
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*
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* If growing the inc function for 'value' will be called the appropriate
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* number of times. So if the caller is holding a reference they may want
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* to drop it.
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*/
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int dm_array_resize(struct dm_array_info *info, dm_block_t root,
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uint32_t old_size, uint32_t new_size,
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const void *value, dm_block_t *new_root)
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__dm_written_to_disk(value);
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/*
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* Frees a whole array. The value_type's decrement operation will be called
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* for all values in the array
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*/
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int dm_array_del(struct dm_array_info *info, dm_block_t root);
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/*
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* Lookup a value in the array
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*
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* info - describes the array
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* root - root block of the array
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* index - array index
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* value - the value to be read. Will be in on-disk format of course.
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*
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* -ENODATA will be returned if the index is out of bounds.
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*/
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int dm_array_get_value(struct dm_array_info *info, dm_block_t root,
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uint32_t index, void *value);
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/*
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* Set an entry in the array.
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*
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* info - describes the array
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* root - root block of the array
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* index - array index
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* value - value to be written to disk. Make sure you confirm the value is
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* in on-disk format with__dm_bless_for_disk() before calling.
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* new_root - the new root block
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*
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* The old value being overwritten will be decremented, the new value
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* incremented.
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*
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* -ENODATA will be returned if the index is out of bounds.
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*/
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int dm_array_set_value(struct dm_array_info *info, dm_block_t root,
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uint32_t index, const void *value, dm_block_t *new_root)
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__dm_written_to_disk(value);
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/*
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* Walk through all the entries in an array.
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*
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* info - describes the array
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* root - root block of the array
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* fn - called back for every element
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* context - passed to the callback
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*/
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int dm_array_walk(struct dm_array_info *info, dm_block_t root,
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int (*fn)(void *context, uint64_t key, void *leaf),
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void *context);
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/*----------------------------------------------------------------*/
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#endif /* _LINUX_DM_ARRAY_H */
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