If bpf(4) has not been compiled into the kernel, initialize the bpf interface

pointer to a zeroed, statically allocated bpf_if structure. This way the
LIST_EMPTY() macro will always return true. This allows us to remove the
additional unconditional memory reference for each packet in the fast path.

Discussed with:	sam

2 files changed, 6 insertions, 1 deletions

diff --git a/sys/net/bpf.c b/sys/net/bpf.c
index 00a95c8..532dc96 100644
--- a/sys/net/bpf.c
+++ b/sys/net/bpf.c
@@ -1790,6 +1790,7 @@ SYSINIT(bpfdev,SI_SUB_DRIVERS,SI_ORDER_MIDDLE,bpf_drvinit,NULL)
  * A 'better' implementation would allow the core bpf functionality
  * to be loaded at runtime.
  */
+static struct bpf_if bp_null;
 
 void
 bpf_tap(bp, pkt, pktlen)
@@ -1820,6 +1821,8 @@ bpfattach(ifp, dlt, hdrlen)
 	struct ifnet *ifp;
 	u_int dlt, hdrlen;
 {
+
+	bpfattach2(ifp, dlt, hdrlen, &ifp->if_bpf);
 }
 
 void
@@ -1828,6 +1831,8 @@ bpfattach2(ifp, dlt, hdrlen, driverp)
 	u_int dlt, hdrlen;
 	struct bpf_if **driverp;
 {
+
+	*driverp = &bp_null;
 }
 
 void
diff --git a/sys/net/bpf.h b/sys/net/bpf.h
index 0782a66..487784a 100644
--- a/sys/net/bpf.h
+++ b/sys/net/bpf.h
@@ -630,7 +630,7 @@ static __inline int
 bpf_peers_present(struct bpf_if *bpf)
 {
 
-	if (bpf && !LIST_EMPTY(&bpf->bif_dlist))
+	if (!LIST_EMPTY(&bpf->bif_dlist))
 		return (1);
 	return (0);
 }