[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>

1 files changed, 65 insertions, 0 deletions

diff --git a/Documentation/networking/radiotap-headers.txt b/Documentation/networking/radiotap-headers.txt
index e29e027d9b..953331c798 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>