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authorAndy Green <andy@warmcat.com>2007-07-10 19:29:38 +0200
committerJohn W. Linville <linville@tuxdriver.com>2007-07-12 16:07:24 -0400
commit179f831bc33104d14deb54a52b7a8b43433f8ccc (patch)
tree8834c628a493fbd4aff1e09dc77b334154c6a050 /Documentation/networking/radiotap-headers.txt
parent08d1f2155cd5b21bb3848f46d9747afb1ccd249d (diff)
[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 <andy@warmcat.com> Signed-off-by: Jiri Benc <jbenc@suse.cz> Signed-off-by: John W. Linville <linville@tuxdriver.com>
Diffstat (limited to 'Documentation/networking/radiotap-headers.txt')
-rw-r--r--Documentation/networking/radiotap-headers.txt65
1 files changed, 65 insertions, 0 deletions
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 <net/cfg80211.h>
+
+/* 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 <andy@warmcat.com>