Add preference to interpret radiotap rates with bit 7 set as MCS.

Change-Id: Ib3a3a70e0edbaeba143703d9b5f4f9c5c8d90818
Reviewed-on: https://code.wireshark.org/review/12855
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>

diff --git a/epan/dissectors/packet-ieee80211-radiotap.c b/epan/dissectors/packet-ieee80211-radiotap.c
index 3ba618740e3320c06397a806fc64a8ad6cb11ddb..2246ba7b781b92f13d7f9c552646212699c7bb87 100644 (file)
--- a/epan/dissectors/packet-ieee80211-radiotap.c
+++ b/epan/dissectors/packet-ieee80211-radiotap.c
@@ -223,6 +223,7 @@ static int radiotap_tap = -1;
 
 /* Settings */
 static gboolean radiotap_bit14_fcs = FALSE;
+static gboolean radiotap_interpret_high_rates_as_mcs = FALSE;
 
 struct _radiotap_info {
        guint radiotap_length;
@@ -878,19 +879,9 @@ dissect_radiotap(tvbuff_t * tvb, packet_info * pinfo, proto_tree * tree, void* u
                         * to 11a or 11g, which do exist, or for 11n
                         * implementations that stuff a rate value into
                         * this field, which also appear to exist.
-                        *
-                        * We currently handle that by assuming that
-                        * if the 0x80 bit is set *and* the remaining
-                        * bits have a value between 0 and 15 it's
-                        * an MCS value, otherwise it's a rate.  If
-                        * there are cases where systems that use
-                        * "0x80 + MCS index" for MCS indices > 15,
-                        * or stuff a rate value here between 64 and
-                        * 71.5 Mb/s in here, we'll need a preference
-                        * setting.  Such rates do exist, e.g. 11n
-                        * MCS 7 at 20 MHz with a long guard interval.
                         */
-                       if (rate >= 0x80 && rate <= 0x8f) {
+                       if (radiotap_interpret_high_rates_as_mcs &&
+                                       rate >= 0x80 && rate <= (0x80+76)) {
                                /*
                                 * XXX - we don't know the channel width
                                 * or guard interval length, so we can't
@@ -2663,6 +2654,12 @@ void proto_register_radiotap(void)
                                       "Some generators (e.g. AirPcap) use a non-standard radiotap flag 14 to put "
                                       "the FCS into the header.",
                                       &radiotap_bit14_fcs);
+
+       prefs_register_bool_preference(radiotap_module, "interpret_high_rates_as_mcs",
+                                      "Interpret high rates as MCS",
+                                      "Some generators use rates with bit 7 set to indicate an MCS, e.g. BSD. "
+                                          "others (Linux, AirPcap) do not.",
+                                      &radiotap_interpret_high_rates_as_mcs);
 }
 
 void proto_reg_handoff_radiotap(void)