Re: [PATCH RFC] cfg80211: add new command for reporting wiphy crashes

["Rafał Miłecki" <zajec5@gmail.com>]

On 26.09.2019 13:55, Johannes Berg wrote:
> On Thu, 2019-09-26 at 13:52 +0200, Rafał Miłecki wrote:
>>
>> Indeed my main concert is AP mode. I'm afraid that cfg80211 doesn't
>> cache all settings, consider e.g. nl80211_start_ap(). It builds
>> struct cfg80211_ap_settings using info from nl80211 message and
>> passes it to the driver (rdev_start_ap()). Once it's done it
>> caches only a small subset of all setup data.
>>
>> In other words driver doesn't have enough info to recover interfaces
>> setup.
> 
> So the driver can cache it, just like mac80211.
> 
> You can't seriously be suggesting that the driver doesn't *have* enough
> information - everything passed through it :)

Precisely: it doesn't store (cache) enough info.


>> I meant that hardware has been recovered & is operational again (driver
>> can talk to it). I expected user space to reconfigure all interfaces
>> using the same settings that were used on previous run.
>>
>> If driver were able to recover interfaces setup on its own (with a help
>> of cfg80211) then user space wouldn't need to be involved.
> 
> The driver can do it, mac80211 does. It's just a matter of what the
> driver will do or not.
> 
>> First of all I was wondering how to handle interfaces creation. After a
>> firmware crash we have:
>> 1) Interfaces created in Linux
>> 2) No corresponsing interfaces in firmware
> 
>> Syncing that (re-creating in-firmware firmwares) may be a bit tricky
>> depending on a driver and hardware.
> 
> We do that in mac80211, it works fine. Why would it be tricky?

In brcmfmac on .add_virtual_intf() we:
1) Send request to the FullMAC firmware
2) Wait for a reply
3) On success we create interface
4) We wake up .add_virtual_intf() handler

I'll need to find a way to skip step 3 in recovery path since interface
on host side already exists.


> If something fails, I think we force that interface to go down.
> 
>> For some cases it could be easier to
>> delete all interfaces and ask user space to setup wiphy (create required
>> interfaces) again. I'm not sure if that's acceptable though?
>>
>> If we agree interfaces should stay and driver simply should configure
>> firmware properly, then we need all data as explained earlier. struct
>> cfg80211_ap_settings is not available during runtime. How should we
>> handle that problem?
> 
> You can cache it in the driver in whatever format makes sense.
> 
>> I was aiming for a brutal force solution: just make user space
>> interfaces need a full setup just at they were just created.
> 
> You can still do that btw, just unregister and re-register the wiphy.

OK, so basically I need to work on caching setup data. Should I try
doing that at my selected driver level (brcmfmac)? Or should I focus on
generic solution (cfg80211) and consider offloading mac80211 if
possible?