nfnetlink_queue -- why linear lookup ?

[<alexandre.ferrieux@orange.com>]

Hello,

In nfnetlink_queue.c, when receiving a verdict for a packet, its entry in the 
queue is looked up linearly:

   find_dequeue_entry(struct nfqnl_instance *queue, unsigned int id)
   {
     ...
     list_for_each_entry(i, &queue->queue_list, list) {
       if (i->id == id) {
         entry = i;
         break;
       }
     }
     ...
   }

As a result, in a situation of "highly asynchronous" verdicts, i.e. when we want 
some packets to linger in the queue for some time before reinjection, the mere 
existence of a large number of such "old packets" may incur a nonnegligible cost 
to the system.

So I'm wondering: why is the list implemented as a simple linked list instead of 
an array directly indexed by the id (like file descriptors) ?

Indeed, the list has a configured max size, the passed id can be bound-checked, 
discarded entries can simply hold a NULL, and id reuse is userspace's 
responsibility. So it looks like the array would yield constant-time lookup with 
no extra risk.

What am I missing ?

Thans in advance,

-Alex

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