1 #ifndef CEPH_CRUSH_CRUSH_H 2 #define CEPH_CRUSH_CRUSH_H 3 4 #include <linux/types.h> 5 6 /* 7 * CRUSH is a pseudo-random data distribution algorithm that 8 * efficiently distributes input values (typically, data objects) 9 * across a heterogeneous, structured storage cluster. 10 * 11 * The algorithm was originally described in detail in this paper 12 * (although the algorithm has evolved somewhat since then): 13 * 14 * http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf 15 * 16 * LGPL2 17 */ 18 19 20 #define CRUSH_MAGIC 0x00010000ul /* for detecting algorithm revisions */ 21 22 23 #define CRUSH_MAX_DEPTH 10 /* max crush hierarchy depth */ 24 #define CRUSH_MAX_SET 10 /* max size of a mapping result */ 25 26 27 /* 28 * CRUSH uses user-defined "rules" to describe how inputs should be 29 * mapped to devices. A rule consists of sequence of steps to perform 30 * to generate the set of output devices. 31 */ 32 struct crush_rule_step { 33 __u32 op; 34 __s32 arg1; 35 __s32 arg2; 36 }; 37 38 /* step op codes */ 39 enum { 40 CRUSH_RULE_NOOP = 0, 41 CRUSH_RULE_TAKE = 1, /* arg1 = value to start with */ 42 CRUSH_RULE_CHOOSE_FIRSTN = 2, /* arg1 = num items to pick */ 43 /* arg2 = type */ 44 CRUSH_RULE_CHOOSE_INDEP = 3, /* same */ 45 CRUSH_RULE_EMIT = 4, /* no args */ 46 CRUSH_RULE_CHOOSE_LEAF_FIRSTN = 6, 47 CRUSH_RULE_CHOOSE_LEAF_INDEP = 7, 48 }; 49 50 /* 51 * for specifying choose num (arg1) relative to the max parameter 52 * passed to do_rule 53 */ 54 #define CRUSH_CHOOSE_N 0 55 #define CRUSH_CHOOSE_N_MINUS(x) (-(x)) 56 57 /* 58 * The rule mask is used to describe what the rule is intended for. 59 * Given a ruleset and size of output set, we search through the 60 * rule list for a matching rule_mask. 61 */ 62 struct crush_rule_mask { 63 __u8 ruleset; 64 __u8 type; 65 __u8 min_size; 66 __u8 max_size; 67 }; 68 69 struct crush_rule { 70 __u32 len; 71 struct crush_rule_mask mask; 72 struct crush_rule_step steps[0]; 73 }; 74 75 #define crush_rule_size(len) (sizeof(struct crush_rule) + \ 76 (len)*sizeof(struct crush_rule_step)) 77 78 79 80 /* 81 * A bucket is a named container of other items (either devices or 82 * other buckets). Items within a bucket are chosen using one of a 83 * few different algorithms. The table summarizes how the speed of 84 * each option measures up against mapping stability when items are 85 * added or removed. 86 * 87 * Bucket Alg Speed Additions Removals 88 * ------------------------------------------------ 89 * uniform O(1) poor poor 90 * list O(n) optimal poor 91 * tree O(log n) good good 92 * straw O(n) optimal optimal 93 */ 94 enum { 95 CRUSH_BUCKET_UNIFORM = 1, 96 CRUSH_BUCKET_LIST = 2, 97 CRUSH_BUCKET_TREE = 3, 98 CRUSH_BUCKET_STRAW = 4 99 }; 100 extern const char *crush_bucket_alg_name(int alg); 101 102 struct crush_bucket { 103 __s32 id; /* this'll be negative */ 104 __u16 type; /* non-zero; type=0 is reserved for devices */ 105 __u8 alg; /* one of CRUSH_BUCKET_* */ 106 __u8 hash; /* which hash function to use, CRUSH_HASH_* */ 107 __u32 weight; /* 16-bit fixed point */ 108 __u32 size; /* num items */ 109 __s32 *items; 110 111 /* 112 * cached random permutation: used for uniform bucket and for 113 * the linear search fallback for the other bucket types. 114 */ 115 __u32 perm_x; /* @x for which *perm is defined */ 116 __u32 perm_n; /* num elements of *perm that are permuted/defined */ 117 __u32 *perm; 118 }; 119 120 struct crush_bucket_uniform { 121 struct crush_bucket h; 122 __u32 item_weight; /* 16-bit fixed point; all items equally weighted */ 123 }; 124 125 struct crush_bucket_list { 126 struct crush_bucket h; 127 __u32 *item_weights; /* 16-bit fixed point */ 128 __u32 *sum_weights; /* 16-bit fixed point. element i is sum 129 of weights 0..i, inclusive */ 130 }; 131 132 struct crush_bucket_tree { 133 struct crush_bucket h; /* note: h.size is _tree_ size, not number of 134 actual items */ 135 __u8 num_nodes; 136 __u32 *node_weights; 137 }; 138 139 struct crush_bucket_straw { 140 struct crush_bucket h; 141 __u32 *item_weights; /* 16-bit fixed point */ 142 __u32 *straws; /* 16-bit fixed point */ 143 }; 144 145 146 147 /* 148 * CRUSH map includes all buckets, rules, etc. 149 */ 150 struct crush_map { 151 struct crush_bucket **buckets; 152 struct crush_rule **rules; 153 154 /* 155 * Parent pointers to identify the parent bucket a device or 156 * bucket in the hierarchy. If an item appears more than 157 * once, this is the _last_ time it appeared (where buckets 158 * are processed in bucket id order, from -1 on down to 159 * -max_buckets. 160 */ 161 __u32 *bucket_parents; 162 __u32 *device_parents; 163 164 __s32 max_buckets; 165 __u32 max_rules; 166 __s32 max_devices; 167 }; 168 169 170 /* crush.c */ 171 extern int crush_get_bucket_item_weight(struct crush_bucket *b, int pos); 172 extern void crush_calc_parents(struct crush_map *map); 173 extern void crush_destroy_bucket_uniform(struct crush_bucket_uniform *b); 174 extern void crush_destroy_bucket_list(struct crush_bucket_list *b); 175 extern void crush_destroy_bucket_tree(struct crush_bucket_tree *b); 176 extern void crush_destroy_bucket_straw(struct crush_bucket_straw *b); 177 extern void crush_destroy_bucket(struct crush_bucket *b); 178 extern void crush_destroy(struct crush_map *map); 179 180 #endif 181