Re: [PATCH v5] netfilter: nfnetlink_queue: optimize verdict lookup with hash table

[Scott Mitchell]

> > +     NFQA_CFG_HASH_SIZE,             /* __u32 hash table size (rounded to power of 2) */
>
> This should use the rhashtable implementation, I don't find a good
> reason why this is not used in first place for this enhancement.

Thank you for the review! I can make the changes. Before implementing,
I have a few questions to ensure I understand the preferred approach:

1. For the "perns" allocation comment - which approach did you have in mind:
  a) Shared rhashtable in nfnl_queue_net (initialized in
nfnl_queue_net_init) with key={queue_num, packet_id}
  b) Per-instance rhashtable in nfqnl_instance, with lock refactoring
so initialization happens outside rcu_read_lock
2. The lock refactoring (GFP_ATOMIC → GFP_KERNEL) is independent of
the hash structure choice, correct? We could fix that separately?
3. Can you help me understand the trade-offs you considered for
rhashtable vs hlist_head? Removing the API makes sense, and I want to
better understand how to weigh that against runtime overhead (RCU,
locks, atomic ops) for future design decisions.

I'll use a custom hashfn to preserve the current mask-based hashing
for the incrementing IDs.