[v5] ethdev: add flow API to expand RSS flows

diff --git a/lib/librte_ethdev/rte_flow.c b/lib/librte_ethdev/rte_flow.c
index 2e87e59f3..2b13efca7 100644
--- a/lib/librte_ethdev/rte_flow.c
+++ b/lib/librte_ethdev/rte_flow.c
@@ -526,3 +526,110 @@  rte_flow_copy(struct rte_flow_desc *desc, size_t len,
 	}
 	return 0;
 }
+
+/**
+ * Expand RSS flows into several possible flows according to the RSS hash
+ * fields requested and the driver capabilities.
+ */
+int
+rte_flow_expand_rss(struct rte_flow_expand_rss *buf, size_t size,
+		    const struct rte_flow_item *pattern, uint64_t types,
+		    const struct rte_flow_expand_node graph[],
+		    int graph_root_index)
+{
+	const int elt_n = 8;
+	const struct rte_flow_item *item;
+	const struct rte_flow_expand_node *node = &graph[graph_root_index];
+	const int *next_node;
+	const int *stack[elt_n];
+	int stack_pos = 0;
+	struct rte_flow_item flow_items[elt_n];
+	unsigned int i;
+	size_t lsize;
+	size_t user_pattern_size = 0;
+	void *addr = NULL;
+
+	lsize = offsetof(struct rte_flow_expand_rss, entry) +
+		elt_n * sizeof(buf->entry[0]);
+	if (lsize <= size) {
+		buf->entry[0].priority = 0;
+		buf->entry[0].pattern = (void *)&buf->entry[elt_n];
+		buf->entries = 0;
+		addr = buf->entry[0].pattern;
+	}
+	for (item = pattern; item->type != RTE_FLOW_ITEM_TYPE_END; item++) {
+		const struct rte_flow_expand_node *next = NULL;
+
+		for (i = 0; node->next && node->next[i]; ++i) {
+			next = &graph[node->next[i]];
+			if (next->type == item->type)
+				break;
+		}
+		if (next)
+			node = next;
+		user_pattern_size += sizeof(*item);
+	}
+	user_pattern_size += sizeof(*item); /* Handle END item. */
+	lsize += user_pattern_size;
+	/* Copy the user pattern in the first entry of the buffer. */
+	if (lsize <= size) {
+		rte_memcpy(addr, pattern, user_pattern_size);
+		addr = (void *)(((uintptr_t)addr) + user_pattern_size);
+		buf->entries = 1;
+	}
+	/* Start expanding. */
+	memset(flow_items, 0, sizeof(flow_items));
+	user_pattern_size -= sizeof(*item);
+	next_node = node->next;
+	stack[stack_pos] = next_node;
+	node = next_node ? &graph[*next_node] : NULL;
+	while (node) {
+		flow_items[stack_pos].type = node->type;
+		if ((node->rss_types & types) == node->rss_types) {
+			/*
+			 * compute the number of items to copy from the
+			 * expansion and copy it.
+			 * When the stack_pos is 0, there are 1 element in it,
+			 * plus the addition END item.
+			 */
+			int elt = stack_pos + 2;
+
+			flow_items[stack_pos + 1].type = RTE_FLOW_ITEM_TYPE_END;
+			lsize += elt * sizeof(*item) + user_pattern_size;
+			if (lsize <= size) {
+				size_t n = elt * sizeof(*item);
+
+				buf->entry[buf->entries].priority =
+					stack_pos + 1;
+				buf->entry[buf->entries].pattern = addr;
+				buf->entries++;
+				rte_memcpy(addr, buf->entry[0].pattern,
+					   user_pattern_size);
+				addr = (void *)(((uintptr_t)addr) +
+						user_pattern_size);
+				rte_memcpy(addr, flow_items, n);
+				addr = (void *)(((uintptr_t)addr) + n);
+			}
+		}
+		/* Go deeper. */
+		if (node->next) {
+			next_node = node->next;
+			if (stack_pos++ == elt_n) {
+				rte_errno = E2BIG;
+				return -rte_errno;
+			}
+			stack[stack_pos] = next_node;
+		} else if (*(next_node + 1)) {
+			/* Follow up with the next possibility. */
+			++next_node;
+		} else {
+			/* Move to the next path. */
+			if (stack_pos)
+				next_node = stack[--stack_pos];
+			next_node++;
+			stack[stack_pos] = next_node;
+		}
+		node = *next_node ? &graph[*next_node] : NULL;
+	};
+	return lsize;
+}
diff --git a/lib/librte_ethdev/rte_flow_driver.h b/lib/librte_ethdev/rte_flow_driver.h
index 1c90c600d..db87f4a51 100644
--- a/lib/librte_ethdev/rte_flow_driver.h
+++ b/lib/librte_ethdev/rte_flow_driver.h
@@ -114,6 +114,64 @@  struct rte_flow_ops {
 const struct rte_flow_ops *
 rte_flow_ops_get(uint16_t port_id, struct rte_flow_error *error);
 
+/** Helper macro to build input graph for rte_flow_expand_rss(). */
+#define RTE_FLOW_EXPAND_RSS_NEXT(...) \
+	(const int []){ \
+		__VA_ARGS__, 0, \
+	}
+
+/** Node object of input graph for rte_flow_expand_rss(). */
+struct rte_flow_expand_node {
+	const int *const next;
+	/**< List of next node indexes. Index 0 is interpreted as a
+	 * terminator. */
+	const enum rte_flow_item_type type;
+	/**< Pattern item type of current node. */
+	uint64_t rss_types;
+	/**< RSS types bit-field associated with this node (see ETH_RSS_*
+	 * definitions).*/
+};
+
+/** Object returned by rte_flow_expand_rss(). */
+struct rte_flow_expand_rss {
+	uint32_t entries;
+	/**< Number of entries @p patterns and @p priorities. */
+	struct {
+		struct rte_flow_item *pattern; /**< Expanded pattern array. */
+		uint32_t priority; /**< Priority offset for each expansion. */
+	} entry[];
+};
+
+/**
+ * Expand RSS flows into several possible flows according to the RSS hash
+ * fields requested and the driver capabilities.
+ *
+ * @param[out] buf
+ *   Buffer to store the result expansion.
+ * @param[in] size
+ *   Buffer size in bytes. If 0, @p buf can be NULL.
+ * @param[in] pattern
+ *   User flow pattern.
+ * @param[in] types
+ *   RSS types to expand (see ETH_RSS_* definitions).
+ * @param[in] graph.
+ *   Input graph to expand @p pattern according to @p types.
+ * @param[in] graph_root_index
+ *   Index of root node in @p graph, typically 0.
+ *
+ * @return
+ *   A positive value representing the size of @p buf in bytes regardless of
+ *   @p size on success, a negative errno value otherwise and rte_errno is
+ *   set, the following errors are defined:
+ *
+ *   -E2BIG: graph-depth @p graph is too deep.
+ */
+int
+rte_flow_expand_rss(struct rte_flow_expand_rss *buf, size_t size,
+		    const struct rte_flow_item *pattern, uint64_t types,
+		    const struct rte_flow_expand_node graph[],
+		    int graph_root_index);
+
 #ifdef __cplusplus
 }
 #endif