netdev - Re: [PATCH] `iwlist scan` fails with many networks available

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Date:   Sun, 11 Aug 2019 08:25:39 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     James Nylen <jnylen@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] `iwlist scan` fails with many networks available

On Sun, 2019-08-11 at 02:08 +0000, James Nylen wrote:
> In 5.x it's still possible for `ieee80211_scan_results` (`iwlist
> scan`) to fail when too many wireless networks are available.  This
> code path is used by `wicd`.
> 
> Previously: https://lkml.org/lkml/2017/4/2/192

This has been known for probably a decade or longer. I don't know why
'wicd' still insists on using wext, unless it's no longer maintained at
all. nl80211 doesn't have this problem at all, and I think gives more
details about the networks found too.

> I've been applying this updated patch to my own kernels since 2017 with
> no issues.  I am sure it is not the ideal way to solve this problem, but
> I'm making my fix available in case it helps others.

I don't think silently dropping data is a good solution.

I suppose we could consider applying a workaround like this if it has a
condition checking that the buffer passed in is the maximum possible
buffer (65535 bytes, due to iw_point::length being u16), but below that
-E2BIG serves well-written implementations as an indicator that they
need to retry with a bigger buffer.

> Please advise on next steps or if this is a dead end.

I think wireless extensions are in fact a dead end and all software
(even 'wicd', which seems to be the lone holdout) should migrate to
nl80211 instead.

johannes