Where Linux 802.11x support needs work

From: Dan Williams (dcbw_at_redhat.com)
Date: 01/25/05

  • Next message: Ingo Molnar: "Re: [patch, 2.6.11-rc2] sched: /proc/sys/kernel/rt_cpu_limit tunable"
    Date:	Tue, 25 Jan 2005 16:47:50 -0500 (EST)
    To: linux-kernel@vger.kernel.org, netdev@oss.sgi.com


    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
    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


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  • Next message: Ingo Molnar: "Re: [patch, 2.6.11-rc2] sched: /proc/sys/kernel/rt_cpu_limit tunable"