common: Add strongly typed element iteration macros

Rather than always iterating elements from frames with pure
u8 pointers, add a type "struct element" that encapsulates
the id/datalen/data format of them.

Then, add the element iteration macros
 * for_each_element
 * for_each_element_id
 * for_each_element_extid

which take, as their first 'argument', such a structure and
iterate through a given u8 array interpreting it as elements.

While at it also add
 * for_each_subelement
 * for_each_subelement_id
 * for_each_subelement_extid

which instead of taking data/length just take an outer element
and use its data/datalen.

Also add for_each_element_completed() to determine if any of
the loops above completed, i.e., it was able to parse all of
the elements successfully and no data remained.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

src/common/ieee802_11_common.h

@@ -12,6 +12,12 @@
 #include "defs.h"
 #include "ieee802_11_defs.h"
 
+struct element {
+	u8 id;
+	u8 datalen;
+	u8 data[];
+} STRUCT_PACKED;
+
 struct hostapd_hw_modes;
 
 #define MAX_NOF_MB_IES_SUPPORTED 5
@@ -214,4 +220,51 @@ int ieee802_11_parse_candidate_list(const char *pos, u8 *nei_rep,
 
 int ieee802_11_ext_capab(const u8 *ie, unsigned int capab);
 
+/* element iteration helpers */
+#define for_each_element(_elem, _data, _datalen)			\
+	for (_elem = (const struct element *) (_data);			\
+	     (const u8 *) (_data) + (_datalen) - (const u8 *) _elem >=	\
+		(int) sizeof(*_elem) &&					\
+	     (const u8 *) (_data) + (_datalen) - (const u8 *) _elem >=	\
+		(int) sizeof(*_elem) + _elem->datalen;			\
+	     _elem = (const struct element *) (_elem->data + _elem->datalen))
+
+#define for_each_element_id(element, _id, data, datalen)		\
+	for_each_element(element, data, datalen)			\
+		if (element->id == (_id))
+
+#define for_each_element_extid(element, extid, _data, _datalen)		\
+	for_each_element(element, _data, _datalen)			\
+		if (element->id == WLAN_EID_EXTENSION &&		\
+		    element->datalen > 0 &&				\
+		    element->data[0] == (extid))
+
+#define for_each_subelement(sub, element)				\
+	for_each_element(sub, (element)->data, (element)->datalen)
+
+#define for_each_subelement_id(sub, id, element)			\
+	for_each_element_id(sub, id, (element)->data, (element)->datalen)
+
+#define for_each_subelement_extid(sub, extid, element)			\
+	for_each_element_extid(sub, extid, (element)->data, (element)->datalen)
+
+/**
+ * for_each_element_completed - Determine if element parsing consumed all data
+ * @element: Element pointer after for_each_element() or friends
+ * @data: Same data pointer as passed to for_each_element() or friends
+ * @datalen: Same data length as passed to for_each_element() or friends
+ *
+ * This function returns 1 if all the data was parsed or considered
+ * while walking the elements. Only use this if your for_each_element()
+ * loop cannot be broken out of, otherwise it always returns 0.
+ *
+ * If some data was malformed, this returns %false since the last parsed
+ * element will not fill the whole remaining data.
+ */
+static inline int for_each_element_completed(const struct element *element,
+					     const void *data, size_t datalen)
+{
+	return (const u8 *) element == (const u8 *) data + datalen;
+}
+
 #endif /* IEEE802_11_COMMON_H */