Suricata

It would be nice to have the pcap files for matching rules instead of the whole traffic passed.

What i want to have ist, that i have a rule that was matched to be logged into fast.log and when i want to analyse it i can just use the suitable pcap file.
It would be also ok to have several matched rules gathered into one pcap file.
But i want to prevent insanely huge pcap files with 99% valid traffic wasting the HDD space.

Is this a valid feature request? And if you think it's not too hard to implement can you point me where i could start to write a patch.