[PATCH net v1 1/3] net: introduce helper to resolve hardware timestamps from skb

Kohei Enju
2026-04-29T09:16:46Z

Move the logic that resolves a hardware timestamp from an skb, including
late timestamp resolution via netdev_get_tstamp(), from net/socket.c to
a common helper.

Let's allow other networking code to reuse the same resolution path.

Signed-off-by: Kohei Enju <kohei@enjuk.jp>
---
include/linux/skbuff.h | 11 +++++++++++
net/core/skbuff.c | 27 +++++++++++++++++++++++++++
net/socket.c | 27 +++------------------------
3 files changed, 41 insertions(+), 24 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2bcf78a4de7b..651a5ae8b11c 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4731,6 +4731,17 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb, const struct sk_buff *ack_skb,
void skb_tstamp_tx(struct sk_buff *orig_skb,
struct skb_shared_hwtstamps *hwtstamps);

+/**
+ * skb_get_hwtstamp - resolve a hardware timestamp from an skb
+ * @skb: skb carrying the timestamp
+ * @cycles: true to request the free-running cycle-based timestamp
+ * @if_index: optional return pointer for the originating netdev ifindex
+ *
+ * Return: resolved hardware timestamp, or the stored skb hwtstamp when no
+ * device-specific late timestamp resolution is needed.
+ */
+ktime_t skb_get_hwtstamp(struct sk_buff *skb, bool cycles, int *if_index);
+
/**
* skb_tx_timestamp() - Driver hook for transmit timestamping
*
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 7dad68e3b518..d11f4e2e9391 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5729,6 +5729,33 @@ void skb_tstamp_tx(struct sk_buff *orig_skb,
}
EXPORT_SYMBOL_GPL(skb_tstamp_tx);

+ktime_t skb_get_hwtstamp(struct sk_buff *skb, bool cycles, int *if_index)
+{
+ struct skb_shared_hwtstamps *shhwtstamps = skb_hwtstamps(skb);
+ struct net_device *orig_dev;
+ ktime_t hwtstamp;
+
+ if (if_index)
+ *if_index = 0;
+
+ if (!(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP_NETDEV))
+ return shhwtstamps->hwtstamp;
+
+ rcu_read_lock();
+ orig_dev = dev_get_by_napi_id(skb_napi_id(skb));
+ if (orig_dev) {
+ if (if_index)
+ *if_index = orig_dev->ifindex;
+ hwtstamp = netdev_get_tstamp(orig_dev, shhwtstamps, cycles);
+ } else {
+ hwtstamp = shhwtstamps->hwtstamp;
+ }
+ rcu_read_unlock();
+
+ return hwtstamp;
+}
+EXPORT_SYMBOL_GPL(skb_get_hwtstamp);
+
#ifdef CONFIG_WIRELESS
void skb_complete_wifi_ack(struct sk_buff *skb, bool acked)
{
diff --git a/net/socket.c b/net/socket.c
index 22a412fdec07..95b21b16a0fc 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -876,21 +876,7 @@ static bool skb_is_swtx_tstamp(const struct sk_buff *skb, int false_tstamp)
static ktime_t get_timestamp(struct sock *sk, struct sk_buff *skb, int *if_index)
{
bool cycles = READ_ONCE(sk->sk_tsflags) & SOF_TIMESTAMPING_BIND_PHC;
- struct skb_shared_hwtstamps *shhwtstamps = skb_hwtstamps(skb);
- struct net_device *orig_dev;
- ktime_t hwtstamp;
-
- rcu_read_lock();
- orig_dev = dev_get_by_napi_id(skb_napi_id(skb));
- if (orig_dev) {
- *if_index = orig_dev->ifindex;
- hwtstamp = netdev_get_tstamp(orig_dev, shhwtstamps, cycles);
- } else {
- hwtstamp = shhwtstamps->hwtstamp;
- }
- rcu_read_unlock();
-
- return hwtstamp;
+ return skb_get_hwtstamp(skb, cycles, if_index);
}

static void put_ts_pktinfo(struct msghdr *msg, struct sk_buff *skb,
@@ -940,7 +926,6 @@ int skb_get_tx_timestamp(struct sk_buff *skb, struct sock *sk,
{
u32 tsflags = READ_ONCE(sk->sk_tsflags);
ktime_t hwtstamp;
- int if_index = 0;

if ((tsflags & SOF_TIMESTAMPING_SOFTWARE) &&
ktime_to_timespec64_cond(skb->tstamp, ts))
@@ -950,10 +935,7 @@ int skb_get_tx_timestamp(struct sk_buff *skb, struct sock *sk,
skb_is_swtx_tstamp(skb, false))
return -ENOENT;

- if (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP_NETDEV)
- hwtstamp = get_timestamp(sk, skb, &if_index);
- else
- hwtstamp = skb_hwtstamps(skb)->hwtstamp;
+ hwtstamp = get_timestamp(sk, skb, NULL);

if (tsflags & SOF_TIMESTAMPING_BIND_PHC)
hwtstamp = ptp_convert_timestamp(&hwtstamp,
@@ -1033,10 +1015,7 @@ void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
!(tsflags & SOF_TIMESTAMPING_OPT_RX_FILTER))) &&
!skb_is_swtx_tstamp(skb, false_tstamp)) {
if_index = 0;
- if (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP_NETDEV)
- hwtstamp = get_timestamp(sk, skb, &if_index);
- else
- hwtstamp = shhwtstamps->hwtstamp;
+ hwtstamp = get_timestamp(sk, skb, &if_index);

if (tsflags & SOF_TIMESTAMPING_BIND_PHC)
hwtstamp = ptp_convert_timestamp(&hwtstamp,
--
2.53.0