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Where Linux 802.11x support needs work

To: linux-kernel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxx
Subject: Where Linux 802.11x support needs work
From: Dan Williams <dcbw@xxxxxxxxxx>
Date: Tue, 25 Jan 2005 16:47:50 -0500 (EST)
Cc: jgarzik@xxxxxxxxx
Sender: netdev-bounce@xxxxxxxxxxx

This list of stuff that should get fixed in Linux wireless grew out of my 
attempt to put a GUI on top of Linux wireless with NetworkManager 
(  This isn't, of course, a 
demand or anything, and I've been personally slowly fixing stuff up as I 
come to it (orinoco merge, fixing linux-wlan-ng, small kernel wireless 
driver patches), but I don't think anyone has posted a comprehensive list 
of where Linux wireless currently falls a bit short.

I think the biggest issue here is that the Wireless Extensions API has 
stagnated a bit, and driver writers have gone off and done their own thing 
(for example, WPA support) because the WEAPI hasn't shown leadership in 
this area.  That's fixable, and at this point doesn't seem to be a large 
amount of work since the main offender here is only WPA.

Second, there are, for historical reasons most likely, areas where the 
WEAPI has multiple methods of encoding data to/from user space.  For 
example, WE Quality values and WE Frequency/Channel values.  Quality is 
either signed or unsigned 8-bit number, which (I believe) is either a raw 
dBm/rssi value or a percentage value, respectively.  Frequency uses 
exponent & mantissa notation, OR a channel # stuffed into the 
exponent/mantissa structure.  Things like that.

Comments appreciated, and hopefully this may spark some wider effort to 
get a few things fixed.

So without further ado, here's the list:

o  Quality values vary wildly or are absent
   1) atmel doesn't return any quality data from scanned APs
   2) ipw_2100 doesn't return _any_ quality data (as of v1.02)
   3) Different quality methods for almost every driver
      - Prism54 does a quality as a percentage
      - airo mixes use of absolute and relative values in dBm
      - Average and max quality levels for almost all drivers are
         artificial and don't come from the the card in any way

Work Item: normalize quality values.  Wireless extensions supports two
different types of quality data, either percentage or dBm.  PICK ONE.  I 
would recommend reporting only a Percentage value to user space with the 
SIOCGIWSTATS call, and having separate ioctl() calls for getting 
specific dBm/noise values if user-space applications _and_ the driver 
supports it.  We cannot have user-space applications guessing which of 3 
different quality algorithms the driver is reporting.

o  Frequency values vary wildly from iw_get_range
   1) prism54 uses completely different exponent values than airo
   2) airo, atmel, orinoco are the same

Work Item: Normalize frequency values between wireless cards.  Use 
actual frequencies in MHz rather than using Exponent & Mantissa format 
as now.  Force user-space applications to convert channels->frequencies, 
based on what frequencies the driver says it supports. Or, fix drivers 
to report Frequency<->Channel pairs when they report their supported 
frequencies, but the point again is to PICK ONE and make all drivers do 
that.  Remove the guessing-game from user-space and pick one API for 
drivers to use.

o  airo/prism54 seem to have problems with ip6 and cause panic
   1) Some drivers don't NULL out their data after they are done with
      it, causing kernel panics later on down the line.  See Red Hat
      bugzilla #135432 for details, Dave Jones has a patch for the airo
      driver that seems to work better, which is in Red Hat 2.6.10

Work Item: Make sure all drivers dispose of and NULL out their data when 
they close, or fix kernel areas that might depend on that stale data.  
Or whatever the problem is.

o  Not all drivers have correct netlink support, if they even have it
   1) orinoco is too twitchy, sends too many events (shouldn't send them
                during a scan for example)
   2) atmel, airo, and others don't seem to have any netlink support

Work Item: fix all drivers to ensure that when the card successfully 
associates with an access point, that it signals the kernel that its 
network link is "up".

o  Not all drivers support wirless scanning
   1) orinoco driver mainly, support is upstream and is being slowly
      merged into the kernel driver

Work Item: Speed up merge of upstream Orinoco into kernel orinoco

o  Firmware issues
   1) Cisco aironet firmware upload is quite inconsistent, fails with
      5.21 for example.  Firmware <= 5.02 seems to be required for using
      WEP with most access points.  Latest Cisco-provided driver is quite
      different than latest in-kernel driver

Work Item: Figure out licensing issues between Cisco-provided driver for 
2.4 kernel (which is MPL) and in-kernel airo driver (which is GPL).  
Then, figure out what changes were made to the Cisco-provided driver to 
support firmware up to 5.30.17, and make those changes in the in-kernel 
airo driver.

o  Ethtool support for all drivers
   1) viro has done a lot of them, not sure if this is complete.

o  Ad-Hoc mode support is quite flaky or absent from most drivers
   1) prism54 "mgmt tx queue full" errors on otherwise-working cards
   2) madwifi resets bitrate to 0 when switching to ad-hoc mode

Work Item: Fix drivers to support Ad-Hoc mode, attempt to get specs on 
their hardware & registers from manufacturers if we don't have that 
information yet for all "modern" cards.

o  WPA support is lacking or just in-progress, needs much help
   1) The point here is that Wireless Extensions API has severely lagged
      behind the capabilities of current chipsets.  There should be
      support _in_ Wireless Extensions for WPA and its associated
      technologies, instead of what all the drivers do now, which is
      separate, non-standard, private ioctl() calls for WPA settings.

Work Item: standardize on an interface for WPA and its associated 
technologies, and implement that interface in Wireless Extensions API.  
Fix all drivers to use that API rather than private ioctl() calls.  Some 
drivers that support WPA:  atmel, madwifi, prism54, ipw2200.  It would 
also be beneficial in this effort to support the calls that 802.1x 
stacks need (like wpa_supplicant and Open 802.1x) so that they don't 
have to patch the drivers (Open 802.1x) or create special per-driver 
hook modules (wpa_supplicant) to be able to capture the necessary 
authentication packets or set up the card's WPA settings.

o  Drivers deal with hidden ESSIDs differently
   1) ipw2x00 traps " " and runs of \0 and changes it to "<hidden>" in
      the driver, while other drivers just pass the blank string through

Work Item: Standardize all drivers to simply pass an empty string 
through to user-space when the base station does not broadcast its 
ESSID.  Drivers should _not_ be clever about this.

Levels of Importance (my opinion):
1) All drivers _MUST_ support wireless scanning (*cough* orinoco *cough*)
2) WPA support needs to be standardized in Wireless Extensions
3) Consistent (and present) quality data among drivers, both for
    currently connected AP and for scanned APs
4) rtnetlink link notification for all drivers when they associate with
    an AP
5) Ad-Hoc mode support
6) Ethtool support
7) Cisco firmware issues

Attachment: linux-wireless-problems.txt
Description: Text document

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