pcap: Introduce pcap_frame() helper

pcap(), pcapm() and pcapmm() duplicate some code, for the actual writing
to the capture file.  The purpose of pcapm() and pcapmm() not calling
pcap() seems to be to avoid repeatedly calling gettimeofday() and to avoid
printing errors for every packet in a batch if there's a problem.  We can
accomplish that while still sharing code by adding a new helper which
takes the packet timestamp as a parameter.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

pcap.c

@@ -65,6 +65,28 @@ struct pcap_pkthdr {
 	uint32_t len;
 };
 
+/**
+ * pcap_frame() - Capture a single frame to pcap file with given timestamp
+ * @pkt:	Pointer to data buffer, including L2 headers
+ * @len:	L2 packet length
+ * @tv:		Timestamp
+ *
+ * Returns: 0 on success, -errno on error writing to the file
+ */
+static int pcap_frame(const char *pkt, size_t len, const struct timeval *tv)
+{
+	struct pcap_pkthdr h;
+
+	h.tv_sec = tv->tv_sec;
+	h.tv_usec = tv->tv_usec;
+	h.caplen = h.len = len;
+
+	if (write(pcap_fd, &h, sizeof(h)) < 0 || write(pcap_fd, pkt, len) < 0)
+		return -errno;
+
+	return 0;
+}
+
 /**
  * pcap() - Capture a single frame to pcap file
  * @pkt:	Pointer to data buffer, including L2 headers
@@ -72,18 +94,13 @@ struct pcap_pkthdr {
  */
 void pcap(const char *pkt, size_t len)
 {
-	struct pcap_pkthdr h;
 	struct timeval tv;
 
 	if (pcap_fd == -1)
 		return;
 
 	gettimeofday(&tv, NULL);
-	h.tv_sec = tv.tv_sec;
+	if (pcap_frame(pkt, len, &tv) != 0)
-	h.tv_usec = tv.tv_usec;
-	h.caplen = h.len = len;
-
-	if (write(pcap_fd, &h, sizeof(h)) < 0 || write(pcap_fd, pkt, len) < 0)
 		debug("Cannot log packet, length %lu", len);
 }
 
@@ -93,8 +110,6 @@ void pcap(const char *pkt, size_t len)
  */
 void pcapm(const struct msghdr *mh)
 {
-	struct pcap_pkthdr h;
-	struct iovec *iov;
 	struct timeval tv;
 	unsigned int i;
 
@@ -102,24 +117,17 @@ void pcapm(const struct msghdr *mh)
 		return;
 
 	gettimeofday(&tv, NULL);
-	h.tv_sec = tv.tv_sec;
-	h.tv_usec = tv.tv_usec;
 
 	for (i = 0; i < mh->msg_iovlen; i++) {
-		iov = &mh->msg_iov[i];
+		const struct iovec *iov = &mh->msg_iov[i];
-
-		h.caplen = h.len = iov->iov_len - 4;
-
-		if (write(pcap_fd, &h, sizeof(h)) < 0)
-			goto fail;
-		if (write(pcap_fd, (char *)iov->iov_base + 4,
-			  iov->iov_len - 4) < 0)
-			goto fail;
-	}
 
+		if (pcap_frame((char *)iov->iov_base + 4,
+			       iov->iov_len - 4, &tv) != 0) {
+			debug("Cannot log packet, length %lu",
+			      iov->iov_len - 4);
 			return;
-fail:
+		}
-	debug("Cannot log packet, length %lu", iov->iov_len - 4);
+	}
 }
 
 /**
@@ -128,8 +136,6 @@ fail:
  */
 void pcapmm(const struct mmsghdr *mmh, unsigned int vlen)
 {
-	struct pcap_pkthdr h;
-	struct iovec *iov;
 	struct timeval tv;
 	unsigned int i, j;
 
@@ -137,27 +143,21 @@ void pcapmm(const struct mmsghdr *mmh, unsigned int vlen)
 		return;
 
 	gettimeofday(&tv, NULL);
-	h.tv_sec = tv.tv_sec;
-	h.tv_usec = tv.tv_usec;
 
 	for (i = 0; i < vlen; i++) {
 		const struct msghdr *mh = &mmh[i].msg_hdr;
 
 		for (j = 0; j < mh->msg_iovlen; j++) {
-			iov = &mh->msg_iov[j];
+			const struct iovec *iov = &mh->msg_iov[j];
 
-			h.caplen = h.len = iov->iov_len - 4;
+			if (pcap_frame((char *)iov->iov_base + 4,
-
+				       iov->iov_len - 4, &tv) != 0) {
-			if (write(pcap_fd, &h, sizeof(h)) < 0)
+				debug("Cannot log packet, length %lu",
-				goto fail;
+				      iov->iov_len - 4);
-			if (write(pcap_fd, (char *)iov->iov_base + 4,
-				  iov->iov_len - 4) < 0)
-				goto fail;
-		}
-	}
 				return;
-fail:
+			}
-	debug("Cannot log packet, length %lu", iov->iov_len - 4);
+		}
+	}
 }
 
 /**