Re: linkup linkdown monitoring impacts the performance

On Fri, 24 Feb 2006, Robert Story wrote:

>
> On Fri, 24 Feb 2006 10:29:31 +0100 (CET) Peder wrote:
> PCN> If you work on a system with "netlink" support (a linux system, for
> PCN> instance) and don't shrink from a bit of C coding you can make a sol=
ution
> PCN> that gives the alarms immediately, and costs absolutely nothing on
> PCN> run-time. The trick is to open a netlink socket and subscribe to li=
nk
> PCN> change messages. Then generate the alarms using the net-snmp C API
> PCN> interface. There is an example in one of the tutorials, and it work=
s, I
> PCN> have tried it. 100-200 lines of code.
>
> Do you have an example of the netlink watching code?

The "quagga" package uses netlink much the way I suggest (actually I
looked more in the "quagga" code than in the documentation when I wrote my
own piece). Look in the file zebra/rt_netlink.c. The function
netlink_link_change is the place where you recognize the ifUp/ifDown
events - but of course you also need the surrounding infrastructure - the
opening and configuration of the socket, the ordering of this specific
brand of events, the adding of the FD for the socket to the central select
loop etc etc.

I did not find netlink easy to work with - the documentation is sloppy and
complex, and the design is not impressive. It took me something like two
full weeks, with a lot of cheating =3D looking in kernel source, to get the
hang of it - but when you know how to work it, it works like a charm.

And for performance it really beats using /proc for almost everything.

best regards

Peder Chr. N=F8rgaard =09Senior System Developer, M. Sc.
Ericsson Denmark A/S, Telebit Division
Skanderborgvej 232 =09tel: +45 30 91 84 31
DK-8260 Viby J, Denmark fax: +45 89 38 51 01
e-mail: Peder.Chr.Norgaard@ericsson.com
(old e-mail 2000-2003: Peder.C.Norgaard@ted.ericsson.se)
(old e-mail 1992-2000: pcn@tbit.dk)
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