cvs commit: src/sys/netinet ip_icmp.c

Brooks Davis brooks at
Mon Feb 2 16:06:38 PST 2004

On Tue, Feb 03, 2004 at 12:45:13AM +0100, Andre Oppermann wrote:
> Brooks Davis wrote:
> > 
> > On Mon, Feb 02, 2004 at 02:53:16PM -0800, Andre Oppermann wrote:
> > > andre       2004/02/02 14:53:16 PST
> > >
> > >   FreeBSD src repository
> > >
> > >   Modified files:
> > >     sys/netinet          ip_icmp.c
> > >   Log:
> > >   Add sysctl net.inet.icmp.reply_src to specify the interface name
> > >   used for the ICMP reply source in reponse to packets which are not
> > >   directly addressed to us.  By default continue with with normal
> > >   source selection.
> > 
> > Please consider storing the interface index rather then the name.  It is
> > much cheaper to go from index to ifp then name to ifp and the index will
> > be invariant as long as the interface exists.  Sometime in the next week
> > the name will no longer be invariant.
> I considered storing the ifp but the moment a stored ipf disappears
> you get an instant panic.  There is no way to verify if the interface
> pointer is still valid.  And with interface cloning I considered the
> panic risk too high.  The only other way would be to check the ifp every
> time a interface is manipulated and to purge the ifp if its interface is
> gone.  I thought that was too intrusive.

I'm not sugguesting caching the ifp.  I'm suggesting storing the value
of ifp->if_index.  You then use ifnet_byindex to get then the ifp when
needed.  You have to check that it isn't NULL, but you should to be
doing that for the ifunit() call as well since it will return NULL and
cause a panic if the admin makes a typo.

As Juli commented, a SYSCTL_PROC to allow the administrator to get/set
the interface by name is probably the right approach.

-- Brooks

Any statement of the form "X is the one, true Y" is FALSE.
PGP fingerprint 655D 519C 26A7 82E7 2529  9BF0 5D8E 8BE9 F238 1AD4
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