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+#ifndef _CRUSH_CRUSH_H
+#define _CRUSH_CRUSH_H
+
+#include <linux/types.h>
+
+/*
+ * 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):
+ *
+ * http://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf
+ *
+ * LGPL2
+ */
+
+
+#define CRUSH_MAGIC 0x00010000ul /* for detecting algorithm revisions */
+
+
+#define CRUSH_MAX_DEPTH 10 /* max crush hierarchy depth */
+#define CRUSH_MAX_SET 10 /* max size of a mapping result */
+
+
+/*
+ * 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 {
+ __u32 op;
+ __s32 arg1;
+ __s32 arg2;
+};
+
+/* step op codes */
+enum {
+ CRUSH_RULE_NOOP = 0,
+ CRUSH_RULE_TAKE = 1, /* arg1 = value to start with */
+ CRUSH_RULE_CHOOSE_FIRSTN = 2, /* arg1 = num items to pick */
+ /* arg2 = type */
+ CRUSH_RULE_CHOOSE_INDEP = 3, /* same */
+ CRUSH_RULE_EMIT = 4, /* no args */
+ CRUSH_RULE_CHOOSE_LEAF_FIRSTN = 6,
+ CRUSH_RULE_CHOOSE_LEAF_INDEP = 7,
+};
+
+/*
+ * for specifying choose num (arg1) relative to the max parameter
+ * passed to do_rule
+ */
+#define CRUSH_CHOOSE_N 0
+#define CRUSH_CHOOSE_N_MINUS(x) (-(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 {
+ __u8 ruleset;
+ __u8 type;
+ __u8 min_size;
+ __u8 max_size;
+};
+
+struct crush_rule {
+ __u32 len;
+ struct crush_rule_mask mask;
+ struct crush_rule_step steps[0];
+};
+
+#define crush_rule_size(len) (sizeof(struct crush_rule) + \
+ (len)*sizeof(struct crush_rule_step))
+
+
+
+/*
+ * 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) optimal optimal
+ */
+enum {
+ CRUSH_BUCKET_UNIFORM = 1,
+ CRUSH_BUCKET_LIST = 2,
+ CRUSH_BUCKET_TREE = 3,
+ CRUSH_BUCKET_STRAW = 4
+};
+extern const char *crush_bucket_alg_name(int alg);
+
+struct crush_bucket {
+ __s32 id; /* this'll be negative */
+ __u16 type; /* non-zero; type=0 is reserved for devices */
+ __u8 alg; /* one of CRUSH_BUCKET_* */
+ __u8 hash; /* which hash function to use, CRUSH_HASH_* */
+ __u32 weight; /* 16-bit fixed point */
+ __u32 size; /* num items */
+ __s32 *items;
+
+ /*
+ * cached random permutation: used for uniform bucket and for
+ * the linear search fallback for the other bucket types.
+ */
+ __u32 perm_x; /* @x for which *perm is defined */
+ __u32 perm_n; /* num elements of *perm that are permuted/defined */
+ __u32 *perm;
+};
+
+struct crush_bucket_uniform {
+ struct crush_bucket h;
+ __u32 item_weight; /* 16-bit fixed point; all items equally weighted */
+};
+
+struct crush_bucket_list {
+ struct crush_bucket h;
+ __u32 *item_weights; /* 16-bit fixed point */
+ __u32 *sum_weights; /* 16-bit fixed point. element i is sum
+ of weights 0..i, inclusive */
+};
+
+struct crush_bucket_tree {
+ struct crush_bucket h; /* note: h.size is _tree_ size, not number of
+ actual items */
+ __u8 num_nodes;
+ __u32 *node_weights;
+};
+
+struct crush_bucket_straw {
+ struct crush_bucket h;
+ __u32 *item_weights; /* 16-bit fixed point */
+ __u32 *straws; /* 16-bit fixed point */
+};
+
+
+
+/*
+ * CRUSH map includes all buckets, rules, etc.
+ */
+struct crush_map {
+ struct crush_bucket **buckets;
+ struct crush_rule **rules;
+
+ /*
+ * Parent pointers to identify the parent bucket a device or
+ * bucket in the hierarchy. If an item appears more than
+ * once, this is the _last_ time it appeared (where buckets
+ * are processed in bucket id order, from -1 on down to
+ * -max_buckets.
+ */
+ __u32 *bucket_parents;
+ __u32 *device_parents;
+
+ __s32 max_buckets;
+ __u32 max_rules;
+ __s32 max_devices;
+};
+
+
+/* crush.c */
+extern int crush_get_bucket_item_weight(struct crush_bucket *b, int pos);
+extern void crush_calc_parents(struct crush_map *map);
+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(struct crush_bucket *b);
+extern void crush_destroy(struct crush_map *map);
+
+#endif