linux-kernel - `iwlist scan` fails with many networks available

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Message-ID: <CABVa4NgWMkJuyB1P5fwQEYHwqBRiySE+fGQpMKt8zbp+xJ8+rw@mail.gmail.com>
Date:   Sun, 2 Apr 2017 14:39:42 -0700
From:   James Nylen <jnylen@...il.com>
To:     linux-kernel@...r.kernel.org
Subject: `iwlist scan` fails with many networks available

I've spent the past few days in a large hotel and noticed that `iwlist
scan` fails with the error message "Argument list too long".

This seems to be because there are a great many wireless networks in
my vicinity.  See:  https://bugzilla.kernel.org/show_bug.cgi?id=16384

Using `iw` as recommended in that ticket works, but it's not a great
option for me because `wicd` doesn't support it.

If I'm understanding the relevant code correctly, the attached patch
works around the issue by skipping networks that would not fit in the
scan-results buffer and returning partial results instead of just
erroring out.

This is the first time I've modified the kernel code directly.  I have
a couple of questions:

- This seems to be working like I intended, but the condition was a
bit hard to reproduce consistently.  Am I inadvertently breaking
things?
- Is there a better way to accomplish this?  Reading the `iwlist` code
I'm not entirely sure why this is occurring, because it looks like it
should be allocating a dynamic buffer length.

View attachment "wireless-scan-skip-extras.diff" of type "text/plain" (1225 bytes)