Messages in this thread Patch in this message | | | Date | Mon, 21 Oct 2002 18:19:36 -0400 | From | Solomon Peachy <> | Subject | [PATCH] New ARPHRD types |
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Attached is a patch for include/linux/if_arp.h, which adds two new ARPHRD types, ARPHRD_IEEE80211_FULL and ARPHRD_IEEE80211_CAPTURE.
This patch is against 2.4.20-pre8, but it should also go into 2.5.x as well, assuming I'm not flamed into oblivion..
A bit of explanation. First, _FULL:
IEEE 802.11 has a variable "hardware" header length, 24 bytes for most frames but 30 bytes for others. This poses a problem if you want to expose a native 802.11 netdev interface to the OS, as netdev->hardhdr_len et.al. aren't variable.
But wait, isn't there already ARPHRD_IEEE80211? Yes, but unfortunately, common usage of this type assumes 24-byte headers. So if we break this assumption, we break backwards compatibility with existing apps. Remember this is intended for a native 802.11 netdev, and plenty of stuff uses PF_PACKET sockets on these interfaces expecting packets to come and go a certian way. For Rx frames we can play games with the skb->mac.raw pointer, but this won't do for Tx frames.
Onto the _CAPTURE type.
(See http://www.shaftnet.org/~pizza/software/capturefrm.txt for the longwinded version including the header format)
"The original header format for 'monitor mode' or capturing frames was a considerable hack. The document covers a redesign of that format."
That "considerable hack" is ARPHRD_IEEE80211_PRISM, which has since come to be used by many other drivers in lieu of a better way to do things. Unfortunately, there is no version field in the old format, so for the sake of making a clean break we'd like to get a new ARP type defined for it.
This new header is non-hardware specific and has many more useful fields, as well as the removal of a lot of cruft. And there's now version and length fields, so we can expand on this format cleanly in the future and not bother you guys with new ARPHRD types. :)
...
Nothing in the wild is currently using either of these types, but that will change RSN.. and I can't push patches to libpcapðereal until the ARP types are in the kernel and therefore fixed. :)
- Pizza -- Solomon Peachy solomon@linux-wlan.com AbsoluteValue Systems http://www.linux-wlan.com 715-D North Drive +1 (321) 259-0737 (office) Melbourne, FL 32934 +1 (321) 259-0286 (fax) --- /usr/src/linux/include/linux/if_arp.h Mon Oct 14 14:16:29 2002 +++ if_arp.h Mon Oct 21 17:47:29 2002 @@ -83,6 +83,8 @@ #define ARPHRD_IEEE802_TR 800 /* Magic type ident for TR */ #define ARPHRD_IEEE80211 801 /* IEEE 802.11 */ #define ARPHRD_IEEE80211_PRISM 802 /* IEEE 802.11 + Prism2 header */ +#define ARPHRD_IEEE80211_FULL 803 /* IEEE 802.11 w/ fixed headerlen */ +#define ARPHRD_IEEE80211_CAPTURE 804 /* IEEE 802.11 w/ new capture header */ #define ARPHRD_VOID 0xFFFF /* Void type, nothing is known */ [unhandled content-type:application/pgp-signature] | |