[PATCH] libpcapng: fix timestamp wrapping in output files
Quentin Armitage
quentin at armitage.org.uk
Sat May 7 18:12:36 CEST 2022
In pcap_tsc_to_ns(), delta * NSEC_PER_SEC will overflow approx 8
seconds after pcap_init is called when using a TSC with a frequency
of 2.5GHz.
To avoid the overflow, reread the time and TSC once
delta * NSEC_PER_SEC > (1 << 63). In order to ensure that there
is no overflow if there is a several second gap between calls to
pcapng_tsc_to_ns() the actual check to reread the clock is:
delta > ((1ULL << 63) / NSEC_PER_SEC)
Fixes: 8d23ce8f5ee ("pcapng: add new library for writing pcapng files")
Cc: stable at dpdk.org
Signed-off-by: Quentin Armitage <quentin at armitage.org.uk>
---
lib/pcapng/rte_pcapng.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/lib/pcapng/rte_pcapng.c b/lib/pcapng/rte_pcapng.c
index 90b2f5bc69..7770be725f 100644
--- a/lib/pcapng/rte_pcapng.c
+++ b/lib/pcapng/rte_pcapng.c
@@ -34,7 +34,7 @@ struct rte_pcapng {
};
/* For converting TSC cycles to PCAPNG ns format */
-struct pcapng_time {
+static struct pcapng_time {
uint64_t ns;
uint64_t cycles;
} pcapng_time;
@@ -53,7 +53,21 @@ static uint64_t pcapng_tsc_to_ns(uint64_t cycles)
{
uint64_t delta;
+ /* With a TSC frequency of 2.5GHz, delta * NSEC_PER_SEC will
+ * wrap in under 8 seconds. Once half that time has elapsed
+ * reread the system clock and TSC to ensure wrapping does not
+ * occur.
+ */
delta = cycles - pcapng_time.cycles;
+ if (delta > ((1ULL << 63) / NSEC_PER_SEC)) {
+ pcapng_init();
+ if (cycles > pcapng_time.cycles)
+ delta = cycles - pcapng_time.cycles;
+ else {
+ delta = pcapng_time.cycles - cycles;
+ return pcapng_time.ns - (delta * NSEC_PER_SEC) / rte_get_tsc_hz();
+ }
+ }
return pcapng_time.ns + (delta * NSEC_PER_SEC) / rte_get_tsc_hz();
}
--
2.34.1
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