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

From: Johannes Berg <johannes@sipsolutions.net>
To: "Rafał Miłecki" <rafal@milecki.pl>, "Jouni Malinen" <j@w1.fi>,
	"Rafał Miłecki" <zajec5@gmail.com>
Cc: "David S . Miller" <davem@davemloft.net>,
	linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, hostap@lists.infradead.org,
	openwrt-devel@lists.openwrt.org
Subject: Re: [PATCH RFC] cfg80211: add new command for reporting wiphy crashes
Date: Thu, 26 Sep 2019 13:55:04 +0200	[thread overview]
Message-ID: <9ece533700be8237699881312a99cc91c6a71d36.camel@sipsolutions.net> (raw)
In-Reply-To: <4f6f37e5-802c-4504-3dcb-c4a640d138bd@milecki.pl>

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 :)

> 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?

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.

johannes