linux-kernel - Re: [PATCH] enhance usability of /proc/sys/net/ipv4/ip_local_reserved

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Date:	Mon, 12 Mar 2012 11:42:39 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Helge Deller <deller@....de>
Cc:	Octavian Purdila <opurdila@...acom.com>,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Frank Danapfel <fdanapfe@...hat.com>,
	Laszlo Ersek <lersek@...hat.com>,
	Linus <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] enhance usability of
 /proc/sys/net/ipv4/ip_local_reserved_ports

Hello, Helge,

On Sun, 2012-03-11 at 00:36 +0100, Helge Deller wrote:
> When writing to the ip_local_reserved_ports proc file it will currently clear
> all previously reserved ports and update the current list with the one given 
> in the input.
> 
> This behaviour makes it's usage quite hard, for example:
> a) The generic proc filesystem limitation of only handle up to PAGE_SIZE-1
>    characters at maximum may not be sufficient to provide all your wished-to-
>    be-reserved ports at once.

Yes, this should be extended IMHO.

> b) There is no easy way to disable specific given ports, you always need to
>    give the full port list at once. This makes shell scripting hard, since
>    you need to parse everything yourself.
> c) There is no easy way to just add specific ports or port ranges. Again,
>    this would be useful for shell scripts.
> 

These could be calculated in user-space, although it maybe not as easy
as you want.

> The following patch solves this problem by simply extending the parser
> in proc_do_large_bitmap() to accept the keywords "add" and "release" in front
> of given ports or port ranges and to either add or drop the given ports
> from the already existing list.

This looks a little odd, because we do "magic" things with a sysctl
file, which is supposed to be plain text file. Do we have existing
examples?

BTW, as David mentioned, please Cc netdev next time.

Thanks.

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