OSCL-LXR linux-6.0.1/​drivers/​md/​persistent-data/​dm-array.h	Source navigation Diff markup Identifier search General search
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 /*
  * Copyright (C) 2012 Red Hat, Inc.
  *
  * This file is released under the GPL.
  */
 #ifndef _LINUX_DM_ARRAY_H
 #define _LINUX_DM_ARRAY_H
 
 #include "dm-btree.h"
 
 /*----------------------------------------------------------------*/
 
 /*
  * The dm-array is a persistent version of an array.  It packs the data
  * more efficiently than a btree which will result in less disk space use,
  * and a performance boost.  The element get and set operations are still
  * O(ln(n)), but with a much smaller constant.
  *
  * The value type structure is reused from the btree type to support proper
  * reference counting of values.
  *
  * The arrays implicitly know their length, and bounds are checked for
  * lookups and updated.  It doesn't store this in an accessible place
  * because it would waste a whole metadata block.  Make sure you store the
  * size along with the array root in your encompassing data.
  *
  * Array entries are indexed via an unsigned integer starting from zero.
  * Arrays are not sparse; if you resize an array to have 'n' entries then
  * 'n - 1' will be the last valid index.
  *
  * Typical use:
  *
  * a) initialise a dm_array_info structure.  This describes the array
  *    values and ties it into a specific transaction manager.  It holds no
  *    instance data; the same info can be used for many similar arrays if
  *    you wish.
  *
  * b) Get yourself a root.  The root is the index of a block of data on the
  *    disk that holds a particular instance of an array.  You may have a
  *    pre existing root in your metadata that you wish to use, or you may
  *    want to create a brand new, empty array with dm_array_empty().
  *
  * Like the other data structures in this library, dm_array objects are
  * immutable between transactions.  Update functions will return you the
  * root for a _new_ array.  If you've incremented the old root, via
  * dm_tm_inc(), before calling the update function you may continue to use
  * it in parallel with the new root.
  *
  * c) resize an array with dm_array_resize().
  *
  * d) Get a value from the array with dm_array_get_value().
  *
  * e) Set a value in the array with dm_array_set_value().
  *
  * f) Walk an array of values in index order with dm_array_walk().  More
  *    efficient than making many calls to dm_array_get_value().
  *
  * g) Destroy the array with dm_array_del().  This tells the transaction
  *    manager that you're no longer using this data structure so it can
  *    recycle it's blocks.  (dm_array_dec() would be a better name for it,
  *    but del is in keeping with dm_btree_del()).
  */
 
 /*
  * Describes an array.  Don't initialise this structure yourself, use the
  * init function below.
  */
 struct dm_array_info {
     struct dm_transaction_manager *tm;
     struct dm_btree_value_type value_type;
     struct dm_btree_info btree_info;
 };
 
 /*
  * Sets up a dm_array_info structure.  You don't need to do anything with
  * this structure when you finish using it.
  *
  * info - the structure being filled in.
  * tm   - the transaction manager that should supervise this structure.
  * vt   - describes the leaf values.
  */
 void dm_array_info_init(struct dm_array_info *info,
             struct dm_transaction_manager *tm,
             struct dm_btree_value_type *vt);
 
 /*
  * Create an empty, zero length array.
  *
  * info - describes the array
  * root - on success this will be filled out with the root block
  */
 int dm_array_empty(struct dm_array_info *info, dm_block_t *root);
 
 /*
  * Resizes the array.
  *
  * info - describes the array
  * root - the root block of the array on disk
  * old_size - the caller is responsible for remembering the size of
  *            the array
  * new_size - can be bigger or smaller than old_size
  * value - if we're growing the array the new entries will have this value
  * new_root - on success, points to the new root block
  *
  * If growing the inc function for 'value' will be called the appropriate
  * number of times.  So if the caller is holding a reference they may want
  * to drop it.
  */
 int dm_array_resize(struct dm_array_info *info, dm_block_t root,
             uint32_t old_size, uint32_t new_size,
             const void *value, dm_block_t *new_root)
     __dm_written_to_disk(value);
 
 /*
  * Creates a new array populated with values provided by a callback
  * function.  This is more efficient than creating an empty array,
  * resizing, and then setting values since that process incurs a lot of
  * copying.
  *
  * Assumes 32bit values for now since it's only used by the cache hint
  * array.
  *
  * info - describes the array
  * root - the root block of the array on disk
  * size - the number of entries in the array
  * fn - the callback
  * context - passed to the callback
  */
 typedef int (*value_fn)(uint32_t index, void *value_le, void *context);
 int dm_array_new(struct dm_array_info *info, dm_block_t *root,
          uint32_t size, value_fn fn, void *context);
 
 /*
  * Frees a whole array.  The value_type's decrement operation will be called
  * for all values in the array
  */
 int dm_array_del(struct dm_array_info *info, dm_block_t root);
 
 /*
  * Lookup a value in the array
  *
  * info - describes the array
  * root - root block of the array
  * index - array index
  * value - the value to be read.  Will be in on-disk format of course.
  *
  * -ENODATA will be returned if the index is out of bounds.
  */
 int dm_array_get_value(struct dm_array_info *info, dm_block_t root,
                uint32_t index, void *value);
 
 /*
  * Set an entry in the array.
  *
  * info - describes the array
  * root - root block of the array
  * index - array index
  * value - value to be written to disk.  Make sure you confirm the value is
  *         in on-disk format with__dm_bless_for_disk() before calling.
  * new_root - the new root block
  *
  * The old value being overwritten will be decremented, the new value
  * incremented.
  *
  * -ENODATA will be returned if the index is out of bounds.
  */
 int dm_array_set_value(struct dm_array_info *info, dm_block_t root,
                uint32_t index, const void *value, dm_block_t *new_root)
     __dm_written_to_disk(value);
 
 /*
  * Walk through all the entries in an array.
  *
  * info - describes the array
  * root - root block of the array
  * fn - called back for every element
  * context - passed to the callback
  */
 int dm_array_walk(struct dm_array_info *info, dm_block_t root,
           int (*fn)(void *context, uint64_t key, void *leaf),
           void *context);
 
 /*----------------------------------------------------------------*/
 
 /*
  * Cursor api.
  *
  * This lets you iterate through all the entries in an array efficiently
  * (it will preload metadata).
  *
  * I'm using a cursor, rather than a walk function with a callback because
  * the cache target needs to iterate both the mapping and hint arrays in
  * unison.
  */
 struct dm_array_cursor {
     struct dm_array_info *info;
     struct dm_btree_cursor cursor;
 
     struct dm_block *block;
     struct array_block *ab;
     unsigned index;
 };
 
 int dm_array_cursor_begin(struct dm_array_info *info,
               dm_block_t root, struct dm_array_cursor *c);
 void dm_array_cursor_end(struct dm_array_cursor *c);
 
 uint32_t dm_array_cursor_index(struct dm_array_cursor *c);
 int dm_array_cursor_next(struct dm_array_cursor *c);
 int dm_array_cursor_skip(struct dm_array_cursor *c, uint32_t count);
 
 /*
  * value_le is only valid while the cursor points at the current value.
  */
 void dm_array_cursor_get_value(struct dm_array_cursor *c, void **value_le);
 
 /*----------------------------------------------------------------*/
 
 #endif  /* _LINUX_DM_ARRAY_H */

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