[PATCH net v3 5/5] ptp: vclock: preserve missing hardware timestamps

[James Hilliard <james.hilliard1@gmail.com>]

Socket timestamp delivery converts hardware timestamps to a bound
virtual clock before checking whether a hardware timestamp is present.
A zero timestamp means that the packet has no hardware timestamp, but
timecounter_cyc2time() can turn that zero into a nonzero virtual time.
The socket then reports a hardware timestamp which was never supplied.

Return zero without conversion when the input timestamp is absent.
This also covers skb_get_tx_timestamp(), which checks for an absent
timestamp after the same conversion.

This was identified during review of virtual clock sampling changes.

Fixes: d7c088265588 ("net: socket: support hardware timestamp conversion to PHC bound")
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
 drivers/ptp/ptp_vclock.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/ptp/ptp_vclock.c b/drivers/ptp/ptp_vclock.c
index 6675466bc307..4a62047f0ce0 100644
--- a/drivers/ptp/ptp_vclock.c
+++ b/drivers/ptp/ptp_vclock.c
@@ -307,6 +307,8 @@ ktime_t ptp_convert_timestamp(const ktime_t *hwtstamp, int vclock_index)
 	u64 ns;
 
 	ns = ktime_to_ns(*hwtstamp);
+	if (!ns)
+		return 0;
 
 	srcu_idx = srcu_read_lock(&vclock_srcu);
 

-- 
2.53.0