Function bpf_attachd

freebsd/net/bpf.c:713–764

* Attach descriptor to the bpf interface, i.e. make d listen on bp, * then reset its buffers and counters with reset_d(). */

 * then reset its buffers and counters with reset_d().
 */
static void
bpf_attachd(struct bpf_d *d, struct bpf_if *bp)
{
	int op_w;

	BPF_LOCK_ASSERT();

	/*
	 * Save sysctl value to protect from sysctl change
	 * between reads
	 */
	op_w = V_bpf_optimize_writers || d->bd_writer;

	if (d->bd_bif != NULL)
		bpf_detachd_locked(d, false);
	/*
	 * Point d at bp, and add d to the interface's list.
	 * Since there are many applications using BPF for
	 * sending raw packets only (dhcpd, cdpd are good examples)
	 * we can delay adding d to the list of active listeners until
	 * some filter is configured.
	 */

	BPFD_LOCK(d);
	/*
	 * Hold reference to bpif while descriptor uses this interface.
	 */
	bpfif_ref(bp);
	d->bd_bif = bp;
	if (op_w != 0) {
		/* Add to writers-only list */
		CK_LIST_INSERT_HEAD(&bp->bif_wlist, d, bd_next);
		/*
		 * We decrement bd_writer on every filter set operation.
		 * First BIOCSETF is done by pcap_open_live() to set up
		 * snap length. After that appliation usually sets its own
		 * filter.
		 */
		d->bd_writer = 2;
	} else
		CK_LIST_INSERT_HEAD(&bp->bif_dlist, d, bd_next);

	reset_d(d);
	BPFD_UNLOCK(d);
	bpf_bpfd_cnt++;

	CTR3(KTR_NET, "%s: bpf_attach called by pid %d, adding to %s list",
	    __func__, d->bd_pid, d->bd_writer ? "writer" : "active");

	if (op_w == 0)
		EVENTHANDLER_INVOKE(bpf_track, bp->bif_ifp, bp->bif_dlt, 1);
}

/*
 * Check if we need to upgrade our descriptor @d from write-only mode.