let bpf pick the first attached dlt when attaching to an interface.

this is instead of picking the lowest numbered dlt, which was done
to make bpf more predictable with interfaces that attached multiple
DLTs. i think the real problem was that bpf would keep the list in
the reverse order of attachment and would prefer the last dlt.

interfaces that attach multiple DLTs attach ethernet first, which
is what you want the majority of the time anyway. but letting bpf
pick the first one means drivers can control which dlt they want
to default to, regardless of the numeric id behind a dlt.

ok claudio@

1 files changed, 7 insertions, 10 deletions

diff --git a/sys/net/bpf.c b/sys/net/bpf.c
index 1496b2a8d4f..d3015e70118 100644
--- a/sys/net/bpf.c
+++ b/sys/net/bpf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: bpf.c,v 1.227 2024/11/19 23:26:35 dlg Exp $	*/
+/*	$OpenBSD: bpf.c,v 1.228 2024/11/26 10:42:58 dlg Exp $	*/
 /*	$NetBSD: bpf.c,v 1.33 1997/02/21 23:59:35 thorpej Exp $	*/
 
 /*
@@ -1180,22 +1180,19 @@ bpf_setf(struct bpf_d *d, struct bpf_program *fp, u_long cmd)
 int
 bpf_setif(struct bpf_d *d, struct ifreq *ifr)
 {
-	struct bpf_if *bp, *candidate = NULL;
+	struct bpf_if *bp;
 	int error = 0;
 
 	/*
 	 * Look through attached interfaces for the named one.
 	 */
 	TAILQ_FOREACH(bp, &bpf_iflist, bif_next) {
-		if (strcmp(bp->bif_name, ifr->ifr_name) != 0)
-			continue;
-
-		if (candidate == NULL || candidate->bif_dlt > bp->bif_dlt)
-			candidate = bp;
+		if (strcmp(bp->bif_name, ifr->ifr_name) == 0)
+			break;
 	}
 
 	/* Not found. */
-	if (candidate == NULL)
+	if (bp == NULL)
 		return (ENXIO);
 
 	/*
@@ -1208,12 +1205,12 @@ bpf_setif(struct bpf_d *d, struct ifreq *ifr)
 		if ((error = bpf_allocbufs(d)))
 			goto out;
 	}
-	if (candidate != d->bd_bif) {
+	if (bp != d->bd_bif) {
 		/*
 		 * Detach if attached to something else.
 		 */
 		bpf_detachd(d);
-		bpf_attachd(d, candidate);
+		bpf_attachd(d, bp);
 	}
 	bpf_resetd(d);
 out: