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authorAndré Fabian Silva Delgado <emulatorman@parabola.nu>2015-08-05 17:04:01 -0300
committerAndré Fabian Silva Delgado <emulatorman@parabola.nu>2015-08-05 17:04:01 -0300
commit57f0f512b273f60d52568b8c6b77e17f5636edc0 (patch)
tree5e910f0e82173f4ef4f51111366a3f1299037a7b /drivers/md/persistent-data/dm-array.h
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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);
+
+/*
+ * 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);
+
+/*----------------------------------------------------------------*/
+
+#endif /* _LINUX_DM_ARRAY_H */