From 179f831bc33104d14deb54a52b7a8b43433f8ccc Mon Sep 17 00:00:00 2001 From: Andy Green Date: Tue, 10 Jul 2007 19:29:38 +0200 Subject: [PATCH] cfg80211: Radiotap parser Generic code to walk through the fields in a radiotap header, accounting for nasties like extended "field present" bitfields and alignment rules Signed-off-by: Andy Green Signed-off-by: Jiri Benc Signed-off-by: John W. Linville --- Documentation/networking/radiotap-headers.txt | 65 +++++++++++++++++++++++++++ 1 file changed, 65 insertions(+) (limited to 'Documentation/networking/radiotap-headers.txt') diff --git a/Documentation/networking/radiotap-headers.txt b/Documentation/networking/radiotap-headers.txt index e29e027d9be..953331c7984 100644 --- a/Documentation/networking/radiotap-headers.txt +++ b/Documentation/networking/radiotap-headers.txt @@ -84,4 +84,69 @@ Example valid radiotap header 0x01 //<-- antenna +Using the Radiotap Parser +------------------------- + +If you are having to parse a radiotap struct, you can radically simplify the +job by using the radiotap parser that lives in net/wireless/radiotap.c and has +its prototypes available in include/net/cfg80211.h. You use it like this: + +#include + +/* buf points to the start of the radiotap header part */ + +int MyFunction(u8 * buf, int buflen) +{ + int pkt_rate_100kHz = 0, antenna = 0, pwr = 0; + struct ieee80211_radiotap_iterator iterator; + int ret = ieee80211_radiotap_iterator_init(&iterator, buf, buflen); + + while (!ret) { + + ret = ieee80211_radiotap_iterator_next(&iterator); + + if (ret) + continue; + + /* see if this argument is something we can use */ + + switch (iterator.this_arg_index) { + /* + * 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. + */ + case IEEE80211_RADIOTAP_RATE: + /* radiotap "rate" u8 is in + * 500kbps units, eg, 0x02=1Mbps + */ + pkt_rate_100kHz = (*iterator.this_arg) * 5; + break; + + case IEEE80211_RADIOTAP_ANTENNA: + /* radiotap uses 0 for 1st ant */ + antenna = *iterator.this_arg); + break; + + case IEEE80211_RADIOTAP_DBM_TX_POWER: + pwr = *iterator.this_arg; + break; + + default: + break; + } + } /* while more rt headers */ + + if (ret != -ENOENT) + return TXRX_DROP; + + /* discard the radiotap header part */ + buf += iterator.max_length; + buflen -= iterator.max_length; + + ... + +} + Andy Green -- cgit v1.2.3