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

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Date:   Wed, 21 Aug 2019 09:59:20 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     James Nylen <jnylen@...il.com>
Cc:     "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 Tue, 2019-08-13 at 00:43 +0000, James Nylen wrote:
> > 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)
> 
> This is what the latest patch does (attached to my email from
> yesterday / https://lkml.org/lkml/2019/8/10/452 ).

Hmm, yes, you're right. I evidently missed the comparisons to 0xFFFF
there, sorry about that.

> If you'd like to apply it, I'm happy to make any needed revisions.
> Otherwise I'm going to have to keep patching my kernels for this
> issue, unfortunately I don't have the time to try to get wicd to
> migrate to a better solution.

Not sure which would be easier, but ok :-)

Can you please fix the patch to
 1) use /* */ style comments (see
    https://www.kernel.org/doc/html/latest/process/coding-style.html)

 2) remove extra braces (also per coding style)

 3) use U16_MAX instead of 0xFFFF

I'd also consider renaming "maybe_current_ev" to "next_ev" or something
shorter anyway, and would probably argue that rewriting this

> +		if (IS_ERR(maybe_current_ev)) {
> +			err = PTR_ERR(maybe_current_ev);
> +			if (err == -E2BIG) {
> +				// Last BSS failed to copy into buffer.  As
> +				// above, only report an error if `iwlist` will
> +				// retry again with a larger buffer.
> +				if (len >= 0xFFFF) {
> +					err = 0;
> +				}
> +			}
>  			break;
> +		} else {
> +			current_ev = maybe_current_ev;
>  		}


to something like

	next_ev = ...
	if (IS_ERR(next_ev)) {
		err = PTR_ERR(next_ev);
		/* mask error and truncate in case buffer cannot be
                 * increased
                 */
		if (err == -E2BIG && len < U16_MAX)
			err = 0;
		break;
	}

	current_ev = next_ev;


could be more readable, but that's just editorial really.

Thanks,
johannes