libpfctl: introduce state iterator
Allow consumers to start processing states as the kernel supplies them,
rather than having to build a full list and only then start processing.
Especially for very large state tables this can significantly reduce
memory use.
Without this change when retrieving 1M states time -l reports:
real 3.55
user 1.95
sys 1.05
318832 maximum resident set size
194 average shared memory size
15 average unshared data size
127 average unshared stack size
79041 page reclaims
0 page faults
0 swaps
0 block input operations
0 block output operations
15096 messages sent
250001 messages received
0 signals received
22 voluntary context switches
34 involuntary context switchesWith it it reported:
real 3.32
user 1.88
sys 0.86
3220 maximum resident set size
195 average shared memory size
11 average unshared data size
128 average unshared stack size
260 page reclaims
0 page faults
0 swaps
0 block input operations
0 block output operations
15096 messages sent
250001 messages received
0 signals received
21 voluntary context switches
31 involuntary context switchesReviewed by: mjg
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D42091