• Johannes Berg's avatar
    cfg80211/mac80211: better channel handling · f444de05
    Johannes Berg authored
    
    
    Currently (all tested with hwsim) you can do stupid
    things like setting up an AP on a certain channel,
    then adding another virtual interface and making
    that associate on another channel -- this will make
    the beaconing to move channel but obviously without
    the necessary IEs data update.
    
    In order to improve this situation, first make the
    configuration APIs (cfg80211 and nl80211) aware of
    multi-channel operation -- we'll eventually need
    that in the future anyway. There's one userland API
    change and one API addition. The API change is that
    now SET_WIPHY must be called with virtual interface
    index rather than only wiphy index in order to take
    effect for that interface -- luckily all current
    users (hostapd) do that. For monitor interfaces, the
    old setting is preserved, but monitors are always
    slaved to other devices anyway so no guarantees.
    
    The second userland API change is the introduction
    of a per virtual interface SET_CHANNEL command, that
    hostapd should use going forward to make it easier
    to understand what's going on (it can automatically
    detect a kernel with this command).
    
    Other than mac80211, no existing cfg80211 drivers
    are affected by this change because they only allow
    a single virtual interface.
    
    mac80211, however, now needs to be aware that the
    channel settings are per interface now, and needs
    to disallow (for now) real multi-channel operation,
    which is another important part of this patch.
    
    One of the immediate benefits is that you can now
    start hostapd to operate on a hardware that already
    has a connection on another virtual interface, as
    long as you specify the same channel.
    
    Note that two things are left unhandled (this is an
    improvement -- not a complete fix):
    
     * different HT/no-HT modes
    
       currently you could start an HT AP and then
       connect to a non-HT network on the same channel
       which would configure the hardware for no HT;
       that can be fixed fairly easily
    
     * CSA
    
       An AP we're connected to on a virtual interface
       might indicate switching channels, and in that
       case we would follow it, regardless of how many
       other interfaces are operating; this requires
       more effort to fix but is pretty rare after all
    Signed-off-by: default avatarJohannes Berg <johannes@sipsolutions.net>
    Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
    f444de05
core.h 12.9 KB