1 files changed, 93 insertions, 0 deletions
diff --git a/src/crush/mapper.h b/src/crush/mapper.h
new file mode 100644
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+++ b/src/crush/mapper.h
@@ -0,0 +1,93 @@
+#ifndef CEPH_CRUSH_MAPPER_H
+#define CEPH_CRUSH_MAPPER_H
+
+/*
+ * CRUSH functions for find rules and then mapping an input to an
+ * output set.
+ *
+ * LGPL-2.1 or LGPL-3.0
+ */
+
+#include "crush.h"
+
+extern int crush_find_rule(const struct crush_map *map, int ruleset, int type, int size);
+/** @ingroup API
+ *
+ * Map __x__ to __result_max__ items and store them in the __result__
+ * array. The mapping is done by following each step of the rule
+ * __ruleno__. See crush_make_rule(), crush_rule_set_step() and
+ * crush_add_rule() for more information on how the rules are created,
+ * populated and added to the crush __map__.
+ *
+ * The return value is the the number of items in the __result__
+ * array. If the caller asked for __result_max__ items and the return
+ * value is X where X < __result_max__, the content of __result[0,X[__
+ * is defined but the content of __result[X,result_max[__ is
+ * undefined. For example:
+ *
+ *     crush_do_rule(map, ruleno=1, x=1, result, result_max=3,...) == 1
+ *     result[0] is set
+ *     result[1] is undefined
+ *     result[2] is undefined
+ *
+ * An entry in the __result__ array is either an item in the crush
+ * __map__ or ::CRUSH_ITEM_NONE if no item was found. For example:
+ *
+ *     crush_do_rule(map, ruleno=1, x=1, result, result_max=4,...) == 2
+ *     result[0] is CRUSH_ITEM_NONE
+ *     result[1] is item number 5
+ *     result[2] is undefined
+ *     result[3] is undefined
+ *
+ * The __weight__ array contains the probabilities that a leaf is
+ * ignored even if it is selected. It is a 16.16 fixed point
+ * number in the range [0x00000,0x10000]. The lower the value, the
+ * more often the leaf is ignored. For instance:
+ *
+ * - weight[leaf] == 0x00000 == 0.0 always ignore
+ * - weight[leaf] == 0x10000 == 1.0 never ignore
+ * - weight[leaf] == 0x08000 == 0.5 ignore 50% of the time
+ * - weight[leaf] == 0x04000 == 0.25 ignore 75% of the time
+ * - etc.
+ *
+ * During mapping, each leaf is checked against the __weight__ array,
+ * using the leaf as an index. If there is no entry in __weight__ for
+ * the leaf, it is ignored. If there is an entry, the leaf will be
+ * ignored some of the time, depending on the probability.
+ *
+ * The __cwin__ argument must be set as follows:
+ *
+ *         char __cwin__[crush_work_size(__map__, __result_max__)];
+ *         crush_init_workspace(__map__, __cwin__);
+ *
+ * @param map the crush_map
+ * @param ruleno a positive integer < __CRUSH_MAX_RULES__
+ * @param x the value to map to __result_max__ items
+ * @param result an array of items of size __result_max__
+ * @param result_max the size of the __result__ array
+ * @param weights an array of weights of size __weight_max__
+ * @param weight_max the size of the __weights__ array
+ * @param cwin must be an char array initialized by crush_init_workspace
+ * @param choose_args weights and ids for each known bucket
+ *
+ * @return 0 on error or the size of __result__ on success
+ */
+extern int crush_do_rule(const struct crush_map *map,
+			 int ruleno,
+			 int x, int *result, int result_max,
+			 const __u32 *weights, int weight_max,
+			 void *cwin, const struct crush_choose_arg *choose_args);
+
+/* Returns the exact amount of workspace that will need to be used
+   for a given combination of crush_map and result_max. The caller can
+   then allocate this much on its own, either on the stack, in a
+   per-thread long-lived buffer, or however it likes. */
+
+static inline size_t crush_work_size(const struct crush_map *map,
+				     int result_max) {
+	return map->working_size + result_max * 3 * sizeof(__u32);
+}
+
+extern void crush_init_workspace(const struct crush_map *m, void *v);
+
+#endif