Re: [PATCH] enhance usability of /proc/sys/net/ipv4/ip_local_reserved_ports
From: Helge Deller
Date: Mon Mar 12 2012 - 17:09:30 EST
On 03/12/2012 04:42 AM, Cong Wang wrote:
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.
Yes, known problem and not easy to fix.
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.
Right.
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?
I don't think the networking sysctl has such tunables.
Overall, ip_local_reserved_ports is the only user of the
large_bitmap function and as such you can't compare the
input/output of this file with other sysctl files which
operate on a limited number of integers/booleans/strings only.
Furthermore my patch does not remove the "plain text"
behaviour of this file. You can still echo plain ports or
port lists into it and a "cat" gives you the same output
as before. It just extends the interface to add/remove
ports more easily if you want.
One somewhat comparable proc file which comes to my mind in this
regard is /proc/scsi/scsi where you can echo commands like
"scsi report-devs 1" and which then reacts. A user of this
interface is e.g. the known rescan-scsi-bus shell script:
http://www.garloff.de/kurt/linux/rescan-scsi-bus.sh-1.25
BTW, as David mentioned, please Cc netdev next time.
Sure. I'll send an updated patch tomorrow and will CC netdev.
Thanks,
Helge
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