radiotap.c File Reference

Radiotap parser. More...

#include "radiotap_iter.h"
#include "platform.h"

Functions
int	ieee80211_radiotap_iterator_init (struct ieee80211_radiotap_iterator *iterator, struct ieee80211_radiotap_header *radiotap_header, int max_length, const struct ieee80211_radiotap_vendor_namespaces *vns)
	radiotap parser iterator initialization More...
int	ieee80211_radiotap_iterator_next (struct ieee80211_radiotap_iterator *iterator)
	return next radiotap parser iterator arg More...

Detailed Description

Radiotap parser.

Copyright 2009 Johannes Berg johan.nosp@m.nes@.nosp@m.sipso.nosp@m.luti.nosp@m.ons.n.nosp@m.et

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License version 2 as published by the Free Software Foundation.

Alternatively, this software may be distributed under the terms of BSD license.

See COPYING for more details.

Function Documentation

int ieee80211_radiotap_iterator_init	(	struct ieee80211_radiotap_iterator *	iterator,
		struct ieee80211_radiotap_header *	radiotap_header,
		int	max_length,
		const struct ieee80211_radiotap_vendor_namespaces *	vns
	)

radiotap parser iterator initialization

Parameters

iterator	radiotap_iterator to initialize
radiotap_header	radiotap header to parse
max_length	total length we can parse into (eg, whole packet length)

Returns

0 or a negative error code if there is a problem.

This function initializes an opaque iterator struct which can then be passed to ieee80211_radiotap_iterator_next() to visit every radiotap argument which is present in the header. It knows about extended present headers and handles them.

How to use: call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator struct ieee80211_radiotap_iterator (no need to init the struct beforehand) checking for a good 0 return code. Then loop calling __ieee80211_radiotap_iterator_next()... it returns either 0, -ENOENT if there are no more args to parse, or -EINVAL if there is a problem. The iterator's this_arg member points to the start of the argument associated with the current argument index that is present, which can be found in the iterator's this_arg_index member. This arg index corresponds to the IEEE80211_RADIOTAP_... defines.

Radiotap header length: You can find the CPU-endian total radiotap header length in iterator->max_length after executing ieee80211_radiotap_iterator_init() successfully.

Alignment Gotcha: You must take care when dereferencing iterator.this_arg for multibyte types... the pointer is not aligned. Use get_unaligned((type *)iterator.this_arg) to dereference iterator.this_arg for type "type" safely on all arches.

Example code: parse.c

int ieee80211_radiotap_iterator_next

(

struct ieee80211_radiotap_iterator *

iterator

)

return next radiotap parser iterator arg

Parameters

iterator

radiotap_iterator to move to next arg (if any)

Returns

0 if there is an argument to handle, -ENOENT if there are no more args or -EINVAL if there is something else wrong.

This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*) in this_arg_index and sets this_arg to point to the payload for the field. It takes care of alignment handling and extended present fields. this_arg can be changed by the caller (eg, incremented to move inside a compound argument like IEEE80211_RADIOTAP_CHANNEL). The args pointed to are in little-endian format whatever the endianess of your CPU.

Alignment Gotcha: You must take care when dereferencing iterator.this_arg for multibyte types... the pointer is not aligned. Use get_unaligned((type *)iterator.this_arg) to dereference iterator.this_arg for type "type" safely on all arches.