Re: [PATCH net-next v2 11/12] net-timestamp: add bpf framework for rx timestamps

On Tue, Oct 15, 2024 at 9:44 AM Willem de Bruijn
[off-list ref] wrote:

Jason Xing wrote:

quoted

From: Jason Xing <kernelxing@tencent.com>

Prepare for later changes in this series. Here I use u32 for
bpf_sock_ops_cb_flags for better extension and introduce a new
rx bpf flag to control separately.

Main change is let userside set through bpf_setsockopt() for
SO_TIMESTAMPING feature.

Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
 include/linux/tcp.h            |  2 +-
 include/net/tcp.h              |  2 +-
 include/uapi/linux/bpf.h       |  5 ++++-
 net/core/filter.c              |  6 +++++-
 net/ipv4/tcp.c                 | 13 ++++++++++++-
 tools/include/uapi/linux/bpf.h |  5 ++++-
 6 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 6a5e08b937b3..e21fd3035962 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h

@@ -446,7 +446,7 @@ struct tcp_sock {

 /* Sock_ops bpf program related variables */
 #ifdef CONFIG_BPF
-     u8      bpf_sock_ops_cb_flags;  /* Control calling BPF programs
+     u32     bpf_sock_ops_cb_flags;  /* Control calling BPF programs
                                       * values defined in uapi/linux/tcp.h
                                       */
      u8      bpf_chg_cc_inprogress:1; /* In the middle of

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 739a9fb83d0c..728db7107074 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h

@@ -423,7 +423,7 @@ int tcp_set_rcvlowat(struct sock *sk, int val);
 int tcp_set_window_clamp(struct sock *sk, int val);
 void tcp_update_recv_tstamps(struct sk_buff *skb,
                           struct scm_timestamping_internal *tss);
-void tcp_recv_timestamp(struct msghdr *msg, const struct sock *sk,
+void tcp_recv_timestamp(struct msghdr *msg, struct sock *sk,
                      struct scm_timestamping_internal *tss);
 void tcp_data_ready(struct sock *sk);
 #ifdef CONFIG_MMU

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1b478ec18ac2..d2754f155cf7 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -6903,8 +6903,11 @@ enum {
      /* Call bpf when the kernel is generating tx timestamps.
       */
      BPF_SOCK_OPS_TX_TIMESTAMPING_OPT_CB_FLAG = (1<<7),
+     /* Call bpf when the kernel is generating rx timestamps.
+      */
+     BPF_SOCK_OPS_RX_TIMESTAMPING_OPT_CB_FLAG = (1<<8),
 /* Mask of all currently supported cb flags */
-     BPF_SOCK_OPS_ALL_CB_FLAGS       = 0xFF,
+     BPF_SOCK_OPS_ALL_CB_FLAGS       = 0x1FF,
 };

 /* List of known BPF sock_ops operators.

diff --git a/net/core/filter.c b/net/core/filter.c
index 3b4afaa273d9..36b357b76f4a 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c

@@ -5216,14 +5216,18 @@ static int bpf_sock_set_timestamping(struct sock *sk,
              return -EINVAL;

      if (!(flags & (SOF_TIMESTAMPING_TX_SCHED | SOF_TIMESTAMPING_TX_SOFTWARE |
-           SOF_TIMESTAMPING_TX_ACK)))
+           SOF_TIMESTAMPING_TX_ACK | SOF_TIMESTAMPING_RX_SOFTWARE)))
              return -EINVAL;

      ret = sock_set_tskey(sk, flags, BPFPROG_TS_REQUESTOR);
      if (ret)
              return ret;

+     if (flags & SOF_TIMESTAMPING_RX_SOFTWARE)
+             sock_enable_timestamp(sk, SOCK_TIMESTAMPING_RX_SOFTWARE);
+
      WRITE_ONCE(sk->sk_tsflags[BPFPROG_TS_REQUESTOR], flags);
+
      static_branch_enable(&bpf_tstamp_control);

      return 0;

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index d37e231b2737..0891b41bc745 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c

@@ -2260,14 +2260,25 @@ static int tcp_zerocopy_receive(struct sock *sk,
 }
 #endif

+static void tcp_bpf_recv_timestamp(struct sock *sk, struct scm_timestamping_internal *tss)
+{
+     struct tcp_sock *tp = tcp_sk(sk);
+
+     if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RX_TIMESTAMPING_OPT_CB_FLAG))
+             return;
+}
+
 /* Similar to __sock_recv_timestamp, but does not require an skb */
-void tcp_recv_timestamp(struct msghdr *msg, const struct sock *sk,
+void tcp_recv_timestamp(struct msghdr *msg, struct sock *sk,
                      struct scm_timestamping_internal *tss)
 {
      int new_tstamp = sock_flag(sk, SOCK_TSTAMP_NEW);
      u32 tsflags = READ_ONCE(sk->sk_tsflags[SOCKETOPT_TS_REQUESTOR]);
      bool has_timestamping = false;

+     if (static_branch_unlikely(&bpf_tstamp_control))
+             tcp_bpf_recv_timestamp(sk, tss);
+
      if (tss->ts[0].tv_sec || tss->ts[0].tv_nsec) {
              if (sock_flag(sk, SOCK_RCVTSTAMP)) {
                      if (sock_flag(sk, SOCK_RCVTSTAMPNS)) {

tcp_recv_timestamp is called from tcp_recvmsg only conditionally:

        if ((cmsg_flags || msg->msg_get_inq) && ret >= 0) {
                if (cmsg_flags & TCP_CMSG_TS)
                        tcp_recv_timestamp(msg, sk, &tss);

How do you get this triggered for your BPF program?

When users use BPF SO_TIMESTAMPING to print rx timestamp, it will use
bpf_setsockopt() to call sock_enable_timestamp() (see this patch), so
the skb will carry a timestamp. In tcp_recvmsg_locked(), cmsg_flags
will be initialized, so tcp_recv_timestamp() will get called.

And also check the other caller, tcp_zc_finalize_rx_tstamp.

Got it, thanks for pointing it out.