Where Linux 802.11x support needs work
From: Dan Williams (dcbw_at_redhat.com)
Date: Tue, 25 Jan 2005 16:47:50 -0500 (EST) To: email@example.com, firstname.lastname@example.org
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
(http://people.redhat.com/dcbw/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
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
5) Ad-Hoc mode support
6) Ethtool support
7) Cisco firmware issues
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- TEXT/plain attachment: linux-wireless-problems.txt