From mboxrd@z Thu Jan 1 00:00:00 1970 From: freeman Subject: Re: limit radiotap header size Date: Tue, 16 Sep 2014 17:01:30 +0000 (UTC) Message-ID: References: <1410869888.2335.6.camel@jlt4.sipsolutions.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org To: radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org List-Id: radiotap@radiotap.org Johannes Berg writes: > > On Mon, 2014-09-15 at 20:10 +0000, freeman wrote: > > > Linux latest kernel (3.16) doc says there are only 13 argument options now. > > Is it still true? > > Where does it say that? I don't think there's any size limit on the > radiotap header since multiple things could show up multiple times etc. > and with the vendor namespace you could carry all kinds of other things. > > > If we are concerned about the size of radiotap header and want to limit the > > set of info we pass to the sniffer, can we arbitrarily remove any arguments > > from the bitmap? I know it is probably designed so, just want to double check :) > > Not really, no, you'd have to adjust the rest of the header as well, > basically parse and recreate it. Why would you want to anyway though? > > johannes > > Johannes Thanks for the help. It seems this kernel doc needs some update http://lxr.free-electrons.com/source/Documentation/networking/radiotap-headers.txt I think I was not clear in last email. If we have a tiny firmware to generate the radiotap header for received packets, and we have limited RAM, it might look attractive to only create a trimmed version radiotap header to the sniffer application. Given the design of the bitmap in the fixed header, I guess it allows us to only include a subset of all arguments, although it is always better to have more info sent up. So in memory constrained systems, how much freedom we have in creating radiotap headers? My dream is that a user application can send a 32bit bitmap to the device driver as a bitmask and the device only sends up those arguments enabled by the mask. Thanks Freeman