Try to handle radiotap Rate values > 127 better.

Use the same heuristic Wireshark uses, i.e. assume that FreeBSD only
reports MCS indices between 0 and 15, and that any other values with the
0x80 bit set are rate values.  (Yes, those do exist.)

Also note, as I did in Wireshark, that it might be possible to extract
from the XChannel and Flags field the additional information to convert
an MCS index from the Rate field into a rate.  (Whether that's possible
depends on what platforms using the FreeBSD convention do with the
channel width and guard interval information.)

diff --git a/print-802_11.c b/print-802_11.c
index 4a1f6263920409ad12144745afe7cc583eadf01a..a94ade2eb3079e61b5592837b299753f04eb9888 100644 (file)
--- a/print-802_11.c
+++ b/print-802_11.c
@@ -1991,19 +1991,46 @@ print_radiotap_field(struct cpack_state *s, u_int32_t bit, u_int8_t *flags,
                break;
        case IEEE80211_RADIOTAP_RATE:
                /*
-                * If the 0x80 bit is set, this is a FreeBSD-style
-                * MCS index.  Print the MCS index, not the rate;
-                * to correctly determine the rate with an MCS index you
-                * need the channel width, i.e. 20MHz/40MHz, and you also
-                * need whether or not the short GI is set or not.
+                * XXX On FreeBSD rate & 0x80 means we have an MCS. On
+                * Linux and AirPcap it does not.  (What about
+                * Mac OS X, NetBSD, OpenBSD, and DragonFly BSD?)
                 *
-                * If you want us to print the rate, use
-                * IEEE80211_RADIOTAP_MCS, not IEEE80211_RADIOTAP_RATE.
+                * This is an issue either for proprietary extensions
+                * 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 (u.u8 & 0x80)
+               if (u.u8 >= 0x80 && u.u8 <= 0x8f) {
+                       /*
+                        * XXX - we don't know the channel width
+                        * or guard interval length, so we can't
+                        * convert this to a data rate.
+                        *
+                        * If you want us to show a data rate,
+                        * use the MCS field, not the Rate field;
+                        * the MCS field includes not only the
+                        * MCS index, it also includes bandwidth
+                        * and guard interval information.
+                        *
+                        * XXX - can we get the channel width
+                        * from XChannel and the guard interval
+                        * information from Flags, at least on
+                        * FreeBSD?
+                        */
                        printf("MCS %u ", u.u8 & 0x7f);
-               else
-                       PRINT_RATE("", u.u8, " Mb/s ");
+               } else
+                       printf("%2.1f Mb/s ", .5*u.u8);
                break;
        case IEEE80211_RADIOTAP_DBM_ANTSIGNAL:
                printf("%ddB signal ", u.i8);