Re: [RFC 9/9] mac80211: implement multi-interface CSA

[Johannes Berg <johannes@sipsolutions.net>]

On Thu, 2014-01-16 at 11:33 +0100, Michal Kazior wrote:

> If you assume a driver supports multi-channel but isn't capable of
> multi-interface CSA you'll be running into timing issues. After you
> detect radar you have a limited time to quiesce. You might end up
> exceeding that limit if you move APs one-by-one.

That probably won't work anyway since you could probably not move them
one by one anyway due to channel context limitations.

> With my patches as they are new hostap will try sending new channel
> switch command but since it doesn't contain ifindex old kernel will
> respond with a -EINVAL and userspace has no way of knowing if the
> command was actually malformed or isn't supported. hostap could still,
> however, work in a best effort manner and fallback to the old command
> variant.

Well, you're looking at it reactively. I was more thinking hostapd might
want to look at it proactively and, for example, refuse setting up
multiple BSSes on a radar channel if multi-switch isn't supported. But
for that, it has to know upfront rather than realizing it reactively
when trying to switch.

johannes