[PATCH v3 2/9] pcap: add pcap_iov()

[Laurent Vivier <lvivier@redhat.com>]

Introduce a new function pcap_iov() to capture packet desribed by an IO
vector.

Move packet header writing to to pcap_header() and use it in
pcap_frame() and pcap_iov().

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---

Notes:
    v3:
      - update rational
      - update comment
      - use strerror(errno)
      - use size_t for io vector length
    
    v2:
      - introduce pcap_header(), a common helper to write
        packet header
      - use writev() rather than write() in a loop
      - add functions comment

 pcap.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++-------
 pcap.h |  1 +
 2 files changed, 56 insertions(+), 7 deletions(-)

diff --git a/pcap.c b/pcap.c
index 501d52d4992b..4e213eea8113 100644
--- a/pcap.c
+++ b/pcap.c
@@ -20,6 +20,7 @@
 #include <sys/time.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/uio.h>
 #include <fcntl.h>
 #include <time.h>
 #include <errno.h>
@@ -31,6 +32,7 @@
 #include "util.h"
 #include "passt.h"
 #include "log.h"
+#include "iov.h"
 
 #define PCAP_VERSION_MINOR 4
 
@@ -65,6 +67,28 @@ struct pcap_pkthdr {
 	uint32_t len;
 };
 
+/*
+ * pcap_header() - Write a pcap packet header to pcap file
+ *
+ * @len:       Length of the packet data.
+ * @tv:        Timestamp for the packet.
+ *
+ * Return: -1 in case of error, otherwise, 0 to indicate success.
+ */
+static int pcap_header(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)
+		return -1;
+
+	return 0;
+}
+
 /**
  * pcap_frame() - Capture a single frame to pcap file with given timestamp
  * @pkt:	Pointer to data buffer, including L2 headers
@@ -75,13 +99,7 @@ struct pcap_pkthdr {
  */
 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)
+	if (pcap_header(len, tv) < 0 || write(pcap_fd, pkt, len) < 0)
 		return -errno;
 
 	return 0;
@@ -130,6 +148,36 @@ void pcap_multiple(const struct iovec *iov, unsigned int n, size_t offset)
 	}
 }
 
+/*
+ * pcap_iov - Write packet data described by a scatter/gather I/O vector (iov)
+ *             to a pcap file descriptor (pcap_fd).
+ *
+ * @iov:       Pointer to the array of struct iovec describing the scatter/gather
+ *             I/O vector containing packet data to write, including L2 header
+ * @n:         Number of elements in the iov array.
+ */
+void pcap_iov(const struct iovec *iov, size_t n)
+{
+	struct timeval tv;
+	size_t len;
+
+	if (pcap_fd == -1)
+		return;
+
+	gettimeofday(&tv, NULL);
+
+	len = iov_size(iov, n);
+
+	if (pcap_header(len, &tv) < 0) {
+		debug("Cannot write pcap header");
+		return;
+	}
+
+	if (writev(pcap_fd, iov, n) < 0)
+		debug("Cannot log packet using writev(): %s\n",
+		      strerror(errno));
+}
+
 /**
  * pcap_init() - Initialise pcap file
  * @c:		Execution context
diff --git a/pcap.h b/pcap.h
index da5a7e846b72..4950f617f4c8 100644
--- a/pcap.h
+++ b/pcap.h
@@ -8,6 +8,7 @@
 
 void pcap(const char *pkt, size_t len);
 void pcap_multiple(const struct iovec *iov, unsigned int n, size_t offset);
+void pcap_iov(const struct iovec *iov, size_t n);
 void pcap_init(struct ctx *c);
 
 #endif /* PCAP_H */
-- 
@@ -8,6 +8,7 @@
 
 void pcap(const char *pkt, size_t len);
 void pcap_multiple(const struct iovec *iov, unsigned int n, size_t offset);
+void pcap_iov(const struct iovec *iov, size_t n);
 void pcap_init(struct ctx *c);
 
 #endif /* PCAP_H */
-- 
2.42.0