On 11/09/2011 05:08 AM, Johannes Berg wrote:
All, I'm thinking about all the off-channel bugs and multi-channel operation. We currently have at least one rather important bug: Almost every call to ieee80211_tx_skb()/ieee80211_xmit() is wrong because it assumes we are on the operating channel. This leads to bugs such as https://bugzilla.redhat.com/attachment.cgi?id=530264 (https://bugzilla.redhat.com/show_bug.cgi?id=749125) where I'd say we are sending a frame for connection monitoring while doing some work on another channel. The other thing is more of a design issue: we have multiple ways to leave the operating channel: scanning& work. Soon we'll have to deal with multi-channel *operation* so we'll have multiple operating channels. I don't even want to have to handle that in mac80211, and I think we'll have to push it into devices (or drivers in some cases). In my opinion, these two ways should be consolidated.
Seems like you could move the scanning into the work logic. That might be a good first step to simplify the off-channel stuff. And, once you get the off-channel stuff working better, it would seem to me that just using that for your off-channel interfaces might be better than trying to re-write everything and force a bunch of new functionality down into drivers. For drivers/NICS that can handle off-channel stuff themselves, hopefully you can add some new API or new arguments to existing API to help leverage that.
Also, as devices (or drivers) get more complex, we find ourselves further and further away from a model where mac80211 is truly fully controlling the device. Given the differences in hardware we support now, I think that it obvious now that we need drivers to be smarter in many cases. How do we want to handle these things? I'm sure I want the drivers to handle multi-channel operation fairly transparently, with multiple (hardware) queues (in the driver), so mac80211 doesn't have to start/stop the queues continuously and can just transmit on that interface, the frame might only go out a bit later.
This sounds like a very big change. I think it will somehow have to be done in stages, maintaining support for the existing API for a while so that drivers can be migrated to the new framework at leisure.
But then what about scanning? Can we, and should we, force such drivers to implement hw_scan? I think maybe we should, and maybe drivers such as brcmsmac& ath9k can share a common scan implementation they call into?
Last thing we need is each driver having it's own complicated off-channel scan logic. It's bad enough having it in one place in mac80211.
Authenticating& associating seems fairly easy, we create a new vif and set it to the right channel and then do everything there -- simpler than what we have now -- but what about FT-OTA? What if the device supports only two channels and is a P2P GO on channel 1 and now wants to roam on the infrastructure connection, say from channel 36 to channel 11? How can we handle that?
With just an improved off-channel work logic, and as much smarts as possible to keep un-necessary channel flops and power-saving changes (and driver resets in general) from happening? Thanks, Ben -- Ben Greear <greearb@xxxxxxxxxxxxxxx> Candela Technologies Inc http://www.candelatech.com -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
