Re: Clarification on the usage of NL80211_SCAN_FLAG_FLUSH

[Matthew Schwartz <matthew.schwartz@linux.dev>]

> On Jan 28, 2026, at 12:39 AM, Johannes Berg <johannes@sipsolutions.net> wrote:
> 
> Hi,
> 
>> Is this intended behavior of NL80211_SCAN_FLAG_FLUSH where it clears all BSS entries regardless of which channels were scanned, or should NL80211_SCAN_FLAG_FLUSH be limited to channels that were scanned in the request which triggered them? The uAPI definition for it is simply "flush cache before scanning", but this seems open to interpretation as to whether it means the entire cache or just the cache on scanned channels.
> 
> Well, AFAICT it has always done that, and so I think regardless of what
> might have been the original intent, it simply is that behaviour now.
> Changing it in the kernel would just end up having to fix two places,
> unless you somehow don't care about running on older kernels without
> fixes.
> 
> I also tend to think it makes sense since the scan could, at least in
> theory, do e.g. colocated scanning, so networks on channels other than
> the ones explicitly listed could be discovered. Trying to do anything
> other than "flush all" would be far more complex.

Okay, thanks for the clarification. I’ll try and take a look at how iwd is using the flush then because it seems like it’s overusing it, or maybe needs some other logic to prevent the connection issues.

Thanks,
Matt

> 
> johannes