Subject: [PATCH bpf-next v12 08/12] bpf: add BPF_SOCK_OPS_TS_HW_OPT_CB callback

From: Jason Xing <[email-masked]>
Date: Tue, 18 Feb 2025 13:01:21 +0800

Support hw SCM_TSTAMP_SND case for bpf timestamping.

Add a new sock_ops callback, BPF_SOCK_OPS_TS_HW_OPT_CB. This
callback will occur at the same timestamping point as the user
space's hardware SCM_TSTAMP_SND. The BPF program can use it to
get the same SCM_TSTAMP_SND timestamp without modifying the
user-space application.

To avoid increasing the code complexity, replace SKBTX_HW_TSTAMP
with SKBTX_HW_TSTAMP_NOBPF instead of changing numerous callers
from driver side using SKBTX_HW_TSTAMP. The new definition of
SKBTX_HW_TSTAMP means the combination tests of socket timestamping
and bpf timestamping. After this patch, drivers can work under the
bpf timestamping.

Considering some drivers don't assign the skb with hardware
timestamp, this patch does the assignment and then BPF program
can acquire the hwstamp from skb directly.

Signed-off-by: Jason Xing <[email-masked]>
---
 include/linux/skbuff.h         |  4 +++-
 include/uapi/linux/bpf.h       |  4 ++++
 net/core/skbuff.c              | 11 +++++++----
 net/dsa/user.c                 |  2 +-
 net/socket.c                   |  2 +-
 tools/include/uapi/linux/bpf.h |  4 ++++
 6 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 76582500c5ea..0b4f1889500d 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -470,7 +470,7 @@ struct skb_shared_hwtstamps {
 /* Definitions for tx_flags in struct skb_shared_info */
 enum {
 	/* generate hardware time stamp */
-	SKBTX_HW_TSTAMP = 1 << 0,
+	SKBTX_HW_TSTAMP_NOBPF = 1 << 0,
 
 	/* generate software time stamp when queueing packet to NIC */
 	SKBTX_SW_TSTAMP = 1 << 1,
@@ -494,6 +494,8 @@ enum {
 	SKBTX_BPF = 1 << 7,
 };
 
+#define SKBTX_HW_TSTAMP		(SKBTX_HW_TSTAMP_NOBPF | SKBTX_BPF)
+
 #define SKBTX_ANY_SW_TSTAMP	(SKBTX_SW_TSTAMP    | \
 				 SKBTX_SCHED_TSTAMP | \
 				 SKBTX_BPF)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index b3bd92281084..f70edd067edf 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7043,6 +7043,10 @@ enum {
 					 * to the nic when SK_BPF_CB_TX_TIMESTAMPING
 					 * feature is on.
 					 */
+	BPF_SOCK_OPS_TS_HW_OPT_CB,	/* Called in hardware phase when
+					 * SK_BPF_CB_TX_TIMESTAMPING feature
+					 * is on.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 03b90f04d0b0..acafa05f7f58 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5547,7 +5547,7 @@ static bool skb_tstamp_tx_report_so_timestamping(struct sk_buff *skb,
 	case SCM_TSTAMP_SCHED:
 		return skb_shinfo(skb)->tx_flags & SKBTX_SCHED_TSTAMP;
 	case SCM_TSTAMP_SND:
-		return skb_shinfo(skb)->tx_flags & (hwtstamps ? SKBTX_HW_TSTAMP :
+		return skb_shinfo(skb)->tx_flags & (hwtstamps ? SKBTX_HW_TSTAMP_NOBPF :
 						    SKBTX_SW_TSTAMP);
 	case SCM_TSTAMP_ACK:
 		return TCP_SKB_CB(skb)->txstamp_ack;
@@ -5568,9 +5568,12 @@ static void skb_tstamp_tx_report_bpf_timestamping(struct sk_buff *skb,
 		op = BPF_SOCK_OPS_TS_SCHED_OPT_CB;
 		break;
 	case SCM_TSTAMP_SND:
-		if (hwtstamps)
-			return;
-		op = BPF_SOCK_OPS_TS_SW_OPT_CB;
+		if (hwtstamps) {
+			op = BPF_SOCK_OPS_TS_HW_OPT_CB;
+			*skb_hwtstamps(skb) = *hwtstamps;
+		} else {
+			op = BPF_SOCK_OPS_TS_SW_OPT_CB;
+		}
 		break;
 	default:
 		return;
diff --git a/net/dsa/user.c b/net/dsa/user.c
index 291ab1b4acc4..794fe553dd77 100644
--- a/net/dsa/user.c
+++ b/net/dsa/user.c
@@ -897,7 +897,7 @@ static void dsa_skb_tx_timestamp(struct dsa_user_priv *p,
 {
 	struct dsa_switch *ds = p->dp->ds;
 
-	if (!(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP))
+	if (!(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP_NOBPF))
 		return;
 
 	if (!ds->ops->port_txtstamp)
diff --git a/net/socket.c b/net/socket.c
index 262a28b59c7f..517de433d4bb 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -676,7 +676,7 @@ void __sock_tx_timestamp(__u32 tsflags, __u8 *tx_flags)
 	u8 flags = *tx_flags;
 
 	if (tsflags & SOF_TIMESTAMPING_TX_HARDWARE) {
-		flags |= SKBTX_HW_TSTAMP;
+		flags |= SKBTX_HW_TSTAMP_NOBPF;
 
 		/* PTP hardware clocks can provide a free running cycle counter
 		 * as a time base for virtual clocks. Tell driver to use the
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 9bd1c7c77b17..7b9652ce7e3c 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7033,6 +7033,10 @@ enum {
 					 * to the nic when SK_BPF_CB_TX_TIMESTAMPING
 					 * feature is on.
 					 */
+	BPF_SOCK_OPS_TS_HW_OPT_CB,	/* Called in hardware phase when
+					 * SK_BPF_CB_TX_TIMESTAMPING feature
+					 * is on.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
-- 
2.43.5