- Improve BPF locking model.

Interface locks and descriptor locks are converted from mutex(9) to rwlock(9).
This greately improves performance: in most common case we need to acquire 1
reader lock instead of 2 mutexes.

- Remove filter(descriptor) (reader) lock in bpf_mtap[2]
This was suggested by glebius@. We protect filter by requesting interface
writer lock on filter change.

- Cover struct bpf_if under BPF_INTERNAL define. This permits including bpf.h
without including rwlock stuff. However, this is is temporary solution,
struct bpf_if should be made opaque for any external caller.

Found by:       Dmitrij Tejblum <tejblum@yandex-team.ru>
Sponsored by:   Yandex LLC

Reviewed by:    glebius (previous version)
Reviewed by:    silence on -net@
Approved by:    (mentor)

MFC after:      3 weeks

1 files changed, 6 insertions, 1 deletions

diff --git a/sys/net/bpf.h b/sys/net/bpf.h
index d4c369d..a347453 100644
--- a/sys/net/bpf.h
+++ b/sys/net/bpf.h
@@ -1092,14 +1092,19 @@ SYSCTL_DECL(_net_bpf);
 
 /*
  * Descriptor associated with each attached hardware interface.
+ * FIXME: this structure is exposed to external callers to speed up
+ * bpf_peers_present() call. However we cover all fields not needed by
+ * this function via BPF_INTERNAL define
  */
 struct bpf_if {
 	LIST_ENTRY(bpf_if)	bif_next;	/* list of all interfaces */
 	LIST_HEAD(, bpf_d)	bif_dlist;	/* descriptor list */
+#ifdef BPF_INTERNAL
 	u_int bif_dlt;				/* link layer type */
 	u_int bif_hdrlen;		/* length of link header */
 	struct ifnet *bif_ifp;		/* corresponding interface */
-	struct mtx	bif_mtx;	/* mutex for interface */
+	struct rwlock bif_lock;		/* interface lock */
+#endif
 };
 
 void	 bpf_bufheld(struct bpf_d *d);