* limit radiotap header size @ 2014-09-15 20:10 freeman [not found] ` <loom.20140915T220101-881-eS7Uydv5nfjZ+VzJOa5vwg@public.gmane.org> 0 siblings, 1 reply; 4+ messages in thread From: freeman @ 2014-09-15 20:10 UTC (permalink / raw) To: radiotap-sUITvd46vNxg9hUCZPvPmw Hi Linux latest kernel (3.16) doc says there are only 13 argument options now. Is it still true? 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 :) Thanks Freeman ^ permalink raw reply [flat|nested] 4+ messages in thread
[parent not found: <loom.20140915T220101-881-eS7Uydv5nfjZ+VzJOa5vwg@public.gmane.org>]
* Re: limit radiotap header size [not found] ` <loom.20140915T220101-881-eS7Uydv5nfjZ+VzJOa5vwg@public.gmane.org> @ 2014-09-16 12:18 ` Johannes Berg 2014-09-16 17:01 ` freeman 0 siblings, 1 reply; 4+ messages in thread From: Johannes Berg @ 2014-09-16 12:18 UTC (permalink / raw) To: freeman; +Cc: radiotap-sUITvd46vNxg9hUCZPvPmw 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 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: limit radiotap header size 2014-09-16 12:18 ` Johannes Berg @ 2014-09-16 17:01 ` freeman [not found] ` <loom.20140916T185055-769-eS7Uydv5nfjZ+VzJOa5vwg@public.gmane.org> 0 siblings, 1 reply; 4+ messages in thread From: freeman @ 2014-09-16 17:01 UTC (permalink / raw) To: radiotap-sUITvd46vNxg9hUCZPvPmw Johannes Berg <johannes@...> 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 ^ permalink raw reply [flat|nested] 4+ messages in thread
[parent not found: <loom.20140916T185055-769-eS7Uydv5nfjZ+VzJOa5vwg@public.gmane.org>]
* Re: limit radiotap header size [not found] ` <loom.20140916T185055-769-eS7Uydv5nfjZ+VzJOa5vwg@public.gmane.org> @ 2014-10-06 14:20 ` Johannes Berg 0 siblings, 0 replies; 4+ messages in thread From: Johannes Berg @ 2014-10-06 14:20 UTC (permalink / raw) To: freeman; +Cc: radiotap-sUITvd46vNxg9hUCZPvPmw On Tue, 2014-09-16 at 17:01 +0000, freeman wrote: > Thanks for the help. > It seems this kernel doc needs some update > http://lxr.free-electrons.com/source/Documentation/networking/radiotap-headers.txt That should probably just point to www.radiotap.org :) > 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? You can chose to include or not include any information that you want. The minimal radiotap header has a zero bitmap and no information at all - but it's also useless. The more data you include, the more useful it becomes. > 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. There's no API to send such down. If you invent API to send such down, then you can of course build the header limited. However, many times the capturing and analysis are done as two separate steps, with the analysis being after the fact on a different system etc., so I'm not sure how useful that would be. For my purposes I'd try to always enable the maximum amount of information... johannes ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2014-10-06 14:20 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2014-09-15 20:10 limit radiotap header size freeman [not found] ` <loom.20140915T220101-881-eS7Uydv5nfjZ+VzJOa5vwg@public.gmane.org> 2014-09-16 12:18 ` Johannes Berg 2014-09-16 17:01 ` freeman [not found] ` <loom.20140916T185055-769-eS7Uydv5nfjZ+VzJOa5vwg@public.gmane.org> 2014-10-06 14:20 ` Johannes Berg
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).