linux/include/linux/crush/crush.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef CEPH_CRUSH_CRUSH_H
#define CEPH_CRUSH_CRUSH_H

#ifdef __KERNEL__
# include <linux/rbtree.h>
# include <linux/types.h>
#else
# include "crush_compat.h"
#endif

/*
 * CRUSH is a pseudo-random data distribution algorithm that
 * efficiently distributes input values (typically, data objects)
 * across a heterogeneous, structured storage cluster.
 *
 * The algorithm was originally described in detail in this paper
 * (although the algorithm has evolved somewhat since then):
 *
 *     https://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf
 *
 * LGPL2
 */


#define CRUSH_MAGIC …

#define CRUSH_MAX_DEPTH …
#define CRUSH_MAX_RULESET …
#define CRUSH_MAX_RULES …

#define CRUSH_MAX_DEVICE_WEIGHT …
#define CRUSH_MAX_BUCKET_WEIGHT …

#define CRUSH_ITEM_UNDEF …
#define CRUSH_ITEM_NONE …

/*
 * CRUSH uses user-defined "rules" to describe how inputs should be
 * mapped to devices.  A rule consists of sequence of steps to perform
 * to generate the set of output devices.
 */
struct crush_rule_step { … };

/* step op codes */
enum { … };

/*
 * for specifying choose num (arg1) relative to the max parameter
 * passed to do_rule
 */
#define CRUSH_CHOOSE_N …
#define CRUSH_CHOOSE_N_MINUS(x) …

/*
 * The rule mask is used to describe what the rule is intended for.
 * Given a ruleset and size of output set, we search through the
 * rule list for a matching rule_mask.
 */
struct crush_rule_mask { … };

struct crush_rule { … };

#define crush_rule_size(len) …



/*
 * A bucket is a named container of other items (either devices or
 * other buckets).  Items within a bucket are chosen using one of a
 * few different algorithms.  The table summarizes how the speed of
 * each option measures up against mapping stability when items are
 * added or removed.
 *
 *  Bucket Alg     Speed       Additions    Removals
 *  ------------------------------------------------
 *  uniform         O(1)       poor         poor
 *  list            O(n)       optimal      poor
 *  tree            O(log n)   good         good
 *  straw           O(n)       better       better
 *  straw2          O(n)       optimal      optimal
 */
enum { … };
extern const char *crush_bucket_alg_name(int alg);

/*
 * although tree was a legacy algorithm, it has been buggy, so
 * exclude it.
 */
#define CRUSH_LEGACY_ALLOWED_BUCKET_ALGS …

struct crush_bucket { … };

/** @ingroup API
 *
 * Replacement weights for each item in a bucket. The size of the
 * array must be exactly the size of the straw2 bucket, just as the
 * item_weights array.
 *
 */
struct crush_weight_set { … };

/** @ingroup API
 *
 * Replacement weights and ids for a given straw2 bucket, for
 * placement purposes.
 *
 * When crush_do_rule() chooses the Nth item from a straw2 bucket, the
 * replacement weights found at __weight_set[N]__ are used instead of
 * the weights from __item_weights__. If __N__ is greater than
 * __weight_set_size__, the weights found at __weight_set_size-1__ are
 * used instead. For instance if __weight_set__ is:
 *
 *    [ [ 0x10000, 0x20000 ],   // position 0
 *      [ 0x20000, 0x40000 ] ]  // position 1
 *
 * choosing the 0th item will use position 0 weights [ 0x10000, 0x20000 ]
 * choosing the 1th item will use position 1 weights [ 0x20000, 0x40000 ]
 * choosing the 2th item will use position 1 weights [ 0x20000, 0x40000 ]
 * etc.
 *
 */
struct crush_choose_arg { … };

/** @ingroup API
 *
 * Replacement weights and ids for each bucket in the crushmap. The
 * __size__ of the __args__ array must be exactly the same as the
 * __map->max_buckets__.
 *
 * The __crush_choose_arg__ at index N will be used when choosing
 * an item from the bucket __map->buckets[N]__ bucket, provided it
 * is a straw2 bucket.
 *
 */
struct crush_choose_arg_map { … };

struct crush_bucket_uniform { … };

struct crush_bucket_list { … };

struct crush_bucket_tree { … };

struct crush_bucket_straw { … };

struct crush_bucket_straw2 { … };



/*
 * CRUSH map includes all buckets, rules, etc.
 */
struct crush_map { … };


/* crush.c */
extern int crush_get_bucket_item_weight(const struct crush_bucket *b, int pos);
extern void crush_destroy_bucket_uniform(struct crush_bucket_uniform *b);
extern void crush_destroy_bucket_list(struct crush_bucket_list *b);
extern void crush_destroy_bucket_tree(struct crush_bucket_tree *b);
extern void crush_destroy_bucket_straw(struct crush_bucket_straw *b);
extern void crush_destroy_bucket_straw2(struct crush_bucket_straw2 *b);
extern void crush_destroy_bucket(struct crush_bucket *b);
extern void crush_destroy_rule(struct crush_rule *r);
extern void crush_destroy(struct crush_map *map);

static inline int crush_calc_tree_node(int i)
{ … }

/*
 * These data structures are private to the CRUSH implementation. They
 * are exposed in this header file because builder needs their
 * definitions to calculate the total working size.
 *
 * Moving this out of the crush map allow us to treat the CRUSH map as
 * immutable within the mapper and removes the requirement for a CRUSH
 * map lock.
 */
struct crush_work_bucket { … };

struct crush_work { … };

#ifdef __KERNEL__
/* osdmap.c */
void clear_crush_names(struct rb_root *root);
void clear_choose_args(struct crush_map *c);
#endif

#endif