Re: Linux Kernel Wireless stack presentation

[Johannes Berg <johannes@sipsolutions.net>]

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On Thu, 2009-08-20 at 10:02 +0300, Rami Rosen wrote:

> http://tuxology.net/wp-content/uploads/2009/08/wirelessLecHerzelinux.pdf

had a quick look

 * almost all drivers support passive scanning -- all the modern ones at
   least -- maybe some old drivers don't, but all using cfg80211 do
 * your presentation is based on old code -- all the code stuff about
   scanning is already outdated in wireless-testing
 * you can scan for multiple specific SSIDs and channels:
   iw wlan0 scan freq 2412 ssid foo bar baz
 * iw has a better IE parser, so showing a result from that may be more
   instructive
 * code stuff about authentication/association is also outdated already
 * the STA_MLME_DISABLED stuff no longer exists
 * AP MLME will never be in the kernel, not just not in the near
   future :)
 * raw packets still go through the mac80211 stack, they arrive in
   monitor_start_xmit() or so
 * four-address format is not necessarily used only for WDS, the
   standard doesn't define uses for it (ToDS = FromDS = 1)
 * an AP may transmit nullfunc (!) frames to tell clients it has no data
   buffered, but it never transmits frames with the PM bit on
 * power timeout 5 is described incorrectly -- it doesn't go to sleep
   for 5 seconds, it actually stays awake for 5 seconds after each
   packet transmission -- the time spent asleep is calculated based on
   the DTIM period etc. Cf. 04fe20372e70685d9f15966216cdffd3795fe590.
 * STA may wake up in response to TIM[AID] == 1 instead of sending
   PS-poll, which we do depends on the timeout (iwconfig wlan0 power
   timeout 0 == PS-poll, iwconfig wlan0 power timeout 100ms == send
   nullfunc and stay awake for 100ms)
 * "paramter" typo
 * ibss is in net/mac80211/ibss.c and has been for quite a while
 * PM in IBSS is not implemented typically
 * s/80211.s/802.11s/
 * s/80211.n/802.11n/
 * you can change the channel with iw (iw phy set freq ...) but it isn't
   really useful unless you're AP/monitor (and rejected otherwise)
 * Fedora no longer updates from wireless-testing afaik
 * wmaster0 is no longer created
 * assigning interface_modes doesn't set the mode, it just sets the
   possible modes :)
 * you can also call iterate_interfaces_atomic() in irq context
 * nobody cares about the wireless extensions version any more :)
 * for sniffing you may care about "iw dev <devname> set monitor <flag>*"

Hey that got long!

johannes

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