Hi.
Is there anyone who has understood of how u32 nexthdr addressing is supposed
to work? (including the "tcp/icmp/.." matches who implicitly uses
nexthdr)
From reading the kernel code it apparently is using the location set by
"offset at", but this seems to only be evaluated on hash parents, and
only
for it''s children..
I.e. the logic for u32 filter rule processing seems to be something like
if all matches true
if terminal filter rule
execute action
else if link rule
if offset plus/at
calculate nexthdr offset
if offset eat
skip any data up to the nexthdr pointer
follow filter link
endif
endif
Think it would be more logical if the nexthdr offset was calculated before
the matches. This way one could create a simple filter rule for matching TCP
data. But I am sure there is some reason to why it is the way it is?
Also, the filter processing seems to be capable of linking filter rules
without using a hash table, but I cannot figure out how to create such a tc
filter rule.
Obviously I am a bit confused.. I have not yet fully got the grips on how to
set up hashed or linked filters. The HOWTO is a bit confusing in this chapter
I think. Would be nice with a explanation why that many filter rules are
created (or if they are not actually many filters, why that many commands are
required). Intuitively it should be sufficient with one tc filter command to
create the hash table rule, and then the tc filter commands to create the
hash chains as required... And the fact that some qdisc has built in filters
does not make the filter concepts easier to understand either (prio)..
Regards
Henrik Nordström
