ipfw add skipto tablearg....
rizzo at iet.unipi.it
Tue Aug 19 18:21:07 UTC 2008
On Wed, Aug 20, 2008 at 04:06:05AM +1000, Ian Smith wrote:
> On Tue, 19 Aug 2008, Luigi Rizzo wrote:
> > On Tue, Aug 19, 2008 at 11:12:04PM +1000, Ian Smith wrote:
> > > Until $someone adds a direct skipto target jump at the virtual machine
> > > code level - big recalc hit when adding/deleting rules/sets I suppose -
> > > it's still the fastest way to get from a to b, where b > a
> > you mean with tables-based skipto targets ? Because the regular
> > skipto has been a constant-time op forever, even in ipfw1 i believe,
> > invalidating the target cache on a change and recomputing it the
> > fly at the first request.
> Thanks; I'd completely missed the caching of skipto targets before, and
> it's all so well commented too. blushing, but glad for the good news.
> But yes I was pondering Julian's patch, which has to lookup_next_rule
> every time, and also Mike's bending of divert reentry rule number in
> ipfw-classifyd with similar intent, which also has to hunt forward in
> linear time for its target rule - or am I missing something else here?
well, you can use a hash table to support that. It shouldn't be so bad
to implement, flow tables already use hash tables so one can reuse the same code.
> > > Speaking of which, should ipfw whinge when asked to skip backwards,
> > > which it can't, confirmed on a recent browse re Mike's ipfw-classifyd
> > > and a local test months ago.
> > right... but the error can only be reliably detected in the kernel,
> > as the rule number is not always known when the rule is added.
> Yes I meant at run-time. On second thoughts, it'd be too easy a way to
actually you can do it at insertion time, it's just that you cannot
do it in userland as other checks before inserting the rule.
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