acl: add comments about internal layout

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>

diff --git a/lib/librte_acl/acl.h b/lib/librte_acl/acl.h
index 217bab3..4dadab5 100644 (file)
--- a/lib/librte_acl/acl.h
+++ b/lib/librte_acl/acl.h
@@ -67,6 +67,44 @@ struct rte_acl_bitset {
 #define        RTE_ACL_NODE_TYPE       (7U << RTE_ACL_TYPE_SHIFT)
 #define        RTE_ACL_NODE_UNDEFINED  UINT32_MAX
 
+/*
+ * ACL RT structure is a set of multibit tries (with stride == 8)
+ * represented by an array of transitions. The next position is calculated
+ * based on the current position and the input byte.
+ * Each transition is 64 bit value with the following format:
+ * | node_type_specific : 32 | node_type : 3 | node_addr : 29 |
+ * For all node types except RTE_ACL_NODE_MATCH, node_addr is an index
+ * to the start of the node in the transtions array.
+ * Few different node types are used:
+ * RTE_ACL_NODE_MATCH:
+ * node_addr value is and index into an array that contains the return value
+ * and its priority for each category.
+ * Upper 32 bits of the transition value are not used for that node type.
+ * RTE_ACL_NODE_QRANGE:
+ * that node consist of up to 5 transitions.
+ * Upper 32 bits are interpreted as 4 signed character values which
+ * are ordered from smallest(INT8_MIN) to largest (INT8_MAX).
+ * These values define 5 ranges:
+ * INT8_MIN <= range[0]  <= ((int8_t *)&transition)[4]
+ * ((int8_t *)&transition)[4] < range[1] <= ((int8_t *)&transition)[5]
+ * ((int8_t *)&transition)[5] < range[2] <= ((int8_t *)&transition)[6]
+ * ((int8_t *)&transition)[6] < range[3] <= ((int8_t *)&transition)[7]
+ * ((int8_t *)&transition)[7] < range[4] <= INT8_MAX
+ * So for input byte value within range[i] i-th transition within that node
+ * will be used.
+ * RTE_ACL_NODE_SINGLE:
+ * always transitions to the same node regardless of the input value.
+ * RTE_ACL_NODE_DFA:
+ * that node consits of up to 256 transitions.
+ * In attempt to conserve space all transitions are divided into 4 consecutive
+ * groups, by 64 transitions per group:
+ * group64[i] contains transitions[i * 64, .. i * 64 + 63].
+ * Upper 32 bits are interpreted as 4 unsigned character values one per group,
+ * which contain index to the start of the given group within the node.
+ * So to calculate transition index within the node for given input byte value:
+ * input_byte - ((uint8_t *)&transition)[4 + input_byte / 64].
+ */
+
 /*
  * Structure of a node is a set of ptrs and each ptr has a bit map
  * of values associated with this transition.