Henrik Nordstrom wrote:
On Tue, 9 Dec 2003, Emmanuel Guiton wrote:

  
My problem is that I do not see which data can be accessed by any of the 
function involved. To be precise, I need to increment a counter each 
time I get one new conntrack. Then I decrement it each time a conntrack 
is destroyed or set as assured (tcp connection).
    

Then the problem is a lot more complex.

Increasing is not a big problem, but the decreasing are as it is hard to 
find which counter to decrease from the conntrack and there is no good 
place to store such information for later without extending the 
ip_conntrack structure unless you implement this as a conntrack 
application protocol helper (can be done if no other conntrack helper is 
needed in the relevant traffic).

Do you really need to decrease the counters?
I think there will remain two alternative ways to deal with the decrementing counter problem:

1.You maintain a hash struture which list any of your concerning conntrack, and while a conntrack facing destroyed then looking  up this hash list if it is on the list.
2.I don't think you need any real helper no matter how simple it can be.But just to extend your target module while matching ip_ct_new put some flags in the help information(conntrack->help.Your_patched_private_help_info)indecate that this is the conntrack you care. And then while a conntrack facing destroyed then looking  up its help info if it is flaged. But if the traffic you wanna filter overlaps with other helpers(eg. ip_conntrack_ftp),then a somewhat dirty way regarding where you put your flags(because help info is only for one helper)is to put them in conntrack->nat.help.Your_patched_private_help_info(for this is relatively a virgin place seldom touched by famous helpers except as I know the pptp helper)

But no matter which above you choose, You can't avoid patching your private destroying code like how ip_conntrack_destroyed(destroying code for NATed conntrack) been called.Because so far we never see any extending conntrack destroying machenism concerning helper's private functionality(like helper->destroy).
Hope this can help ;)!

Regards
Jesse