[dpdk-dev] [PATCH 1/2] net/pcap: support software Tx nanosecond timestamp

[Vivien Didelot <vivien.didelot@gmail.com>]

When capturing packets into a PCAP file, DPDK currently uses
microseconds for the timestamp. But libpcap supports interpreting
tv_usec as nanoseconds depending on the file timestamp precision.

To support this, use PCAP_TSTAMP_PRECISION_NANO when creating the
empty PCAP file as specified by PCAP_OPEN_DEAD(3PCAP) and implement
nanosecond timeval addition. This also ensures that the precision
reported by capinfos is nanoseconds (9).

Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
---
 drivers/net/pcap/rte_eth_pcap.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/net/pcap/rte_eth_pcap.c b/drivers/net/pcap/rte_eth_pcap.c
index b4c79d174..68588c3d7 100644
--- a/drivers/net/pcap/rte_eth_pcap.c
+++ b/drivers/net/pcap/rte_eth_pcap.c
@@ -287,6 +287,8 @@ eth_null_rx(void *queue __rte_unused,
 	return 0;
 }
 
+#define NSEC_PER_SEC	1e9
+
 static inline void
 calculate_timestamp(struct timeval *ts) {
 	uint64_t cycles;
@@ -294,8 +296,14 @@ calculate_timestamp(struct timeval *ts) {
 
 	cycles = rte_get_timer_cycles() - start_cycles;
 	cur_time.tv_sec = cycles / hz;
-	cur_time.tv_usec = (cycles % hz) * 1e6 / hz;
-	timeradd(&start_time, &cur_time, ts);
+	cur_time.tv_usec = (cycles % hz) * NSEC_PER_SEC / hz;
+
+	ts->tv_sec = start_time.tv_sec + cur_time.tv_sec;
+	ts->tv_usec = start_time.tv_usec + cur_time.tv_usec;
+	if (ts->tv_usec > NSEC_PER_SEC) {
+		ts->tv_usec -= NSEC_PER_SEC;
+		ts->tv_sec += 1;
+	}
 }
 
 /*
@@ -475,7 +483,8 @@ open_single_tx_pcap(const char *pcap_filename, pcap_dumper_t **dumper)
 	 * with pcap_dump_open(). We create big enough an Ethernet
 	 * pcap holder.
 	 */
-	tx_pcap = pcap_open_dead(DLT_EN10MB, RTE_ETH_PCAP_SNAPSHOT_LEN);
+	tx_pcap = pcap_open_dead_with_tstamp_precision(DLT_EN10MB,
+			RTE_ETH_PCAP_SNAPSHOT_LEN, PCAP_TSTAMP_PRECISION_NANO);
 	if (tx_pcap == NULL) {
 		PMD_LOG(ERR, "Couldn't create dead pcap");
 		return -1;
-- 
2.26.2