--- libaitio/src/bpf.c	2013/06/25 08:45:50	1.1.2.7
+++ libaitio/src/bpf.c	2013/06/25 09:29:34	1.1.2.10
@@ -163,6 +163,7 @@ io_etherOpen(const char *csIface, int flags, int whdr,
 		io_etherClose(eth, zcbuf);
 		return -1;
 	}
+	memset(&ifr, 0, sizeof ifr);
 	strlcpy(ifr.ifr_name, szStr, sizeof ifr.ifr_name);
 	if (ioctl(eth, BIOCSETIF, &ifr) == -1) {
 		LOGERR;
@@ -198,6 +199,19 @@ io_etherSend(int eth, const void *buf, size_t buflen)
 }
 
 #ifdef __FreeBSD__
+static inline void
+ackZCbuf(struct bpf_zbuf_header * __restrict bzh)
+{
+	atomic_store_rel_int(&bzh->bzh_user_gen, bzh->bzh_kernel_gen);
+}
+
+static inline int
+chkZCbuf(struct bpf_zbuf_header * __restrict bzh)
+{
+	/* return true if userspace owns buffer, and false otherwise. */
+	return (bzh->bzh_user_gen != atomic_load_acq_int(&bzh->bzh_kernel_gen));
+}
+
 static inline ssize_t
 nextZCbuf(void ** __restrict zcache, struct bpf_zbuf * __restrict zbuf, 
 		const void * __restrict buf)
@@ -207,20 +221,24 @@ nextZCbuf(void ** __restrict zcache, struct bpf_zbuf *
 
 	if (!*zcache || *zcache == zbuf->bz_bufb) {
 		bzh = (struct bpf_zbuf_header *) zbuf->bz_bufa;
-		if (bzh->bzh_user_gen != atomic_load_acq_int(&bzh->bzh_kernel_gen)) {
+		if (chkZCbuf(bzh)) {
 			rlen = atomic_load_acq_int(&bzh->bzh_kernel_len);
 			*zcache = zbuf->bz_bufa;
 			if (buf)
 				buf = ((caddr_t) *zcache) + sizeof(struct bpf_zbuf_header);
-		}
+			ackZCbuf(bzh);
+		} else
+			io_SetErr(EAGAIN, "kernel owns the buffer");
 	} else if (*zcache == zbuf->bz_bufa) {
 		bzh = (struct bpf_zbuf_header *) zbuf->bz_bufb;
-		if (bzh->bzh_user_gen != atomic_load_acq_int(&bzh->bzh_kernel_gen)) {
+		if (chkZCbuf(bzh)) {
 			rlen = atomic_load_acq_int(&bzh->bzh_kernel_len);
 			*zcache = zbuf->bz_bufb;
 			if (buf)
 				buf = ((caddr_t) *zcache) + sizeof(struct bpf_zbuf_header);
-		}
+			ackZCbuf(bzh);
+		} else
+			io_SetErr(EAGAIN, "kernel owns the buffer");
 	}
 
 	return rlen;