Re: [PATCH net-next v3 1/4] net_tstamp: add SCM_TS_OPT_ID to provide OPT_ID in control message

SOF_TIMESTAMPING_OPT_ID socket option flag gives a way to correlate TX
timestamps and packets sent via socket. Unfortunately, there is no way
to reliably predict socket timestamp ID value in case of error returned
by sendmsg. For UDP sockets it's impossible because of lockless
nature of UDP transmit, several threads may send packets in parallel. In
case of RAW sockets MSG_MORE option makes things complicated. More
details are in the conversation [1].
This patch adds new control message type to give user-space
software an opportunity to control the mapping between packets and
values by providing ID with each sendmsg for UDP sockets.
The documentation is also added in this patch.

[1] https://lore.kernel.org/netdev/CALCETrU0jB+kg0mhV6A8mrHfTE1D1pr1SD_B9Eaa9aDPfgHdtA@mail.gmail.com/ (local)

Signed-off-by: Vadim Fedorenko <redacted>
---
 Documentation/networking/timestamping.rst | 13 +++++++++++++
 arch/alpha/include/uapi/asm/socket.h      |  2 ++
 arch/mips/include/uapi/asm/socket.h       |  2 ++
 arch/parisc/include/uapi/asm/socket.h     |  2 ++
 arch/sparc/include/uapi/asm/socket.h      |  2 ++
 include/net/inet_sock.h                   |  4 +++-
 include/net/sock.h                        |  2 ++
 include/uapi/asm-generic/socket.h         |  2 ++
 include/uapi/linux/net_tstamp.h           |  7 +++++++
 net/core/sock.c                           |  9 +++++++++
 net/ipv4/ip_output.c                      | 18 +++++++++++++-----
 net/ipv6/ip6_output.c                     | 18 +++++++++++++-----
 12 files changed, 70 insertions(+), 11 deletions(-)

diff --git a/Documentation/networking/timestamping.rst b/Documentation/networking/timestamping.rst
index 5e93cd71f99f..e365526d6bf9 100644
--- a/Documentation/networking/timestamping.rst
+++ b/Documentation/networking/timestamping.rst

@@ -193,6 +193,19 @@ SOF_TIMESTAMPING_OPT_ID:
   among all possibly concurrently outstanding timestamp requests for
   that socket.

+  The process can optionally override the default generated ID, by
+  passing a specific ID with control message SCM_TS_OPT_ID::
+
+    struct msghdr *msg;
+    ...
+    cmsg                        = CMSG_FIRSTHDR(msg);
+    cmsg->cmsg_level            = SOL_SOCKET;
+    cmsg->cmsg_type             = SCM_TS_OPT_ID;
+    cmsg->cmsg_len              = CMSG_LEN(sizeof(__u32));
+    *((__u32 *) CMSG_DATA(cmsg)) = opt_id;
+    err = sendmsg(fd, msg, 0);
+
+
 SOF_TIMESTAMPING_OPT_ID_TCP:
   Pass this modifier along with SOF_TIMESTAMPING_OPT_ID for new TCP
   timestamping applications. SOF_TIMESTAMPING_OPT_ID defines how the

diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
index e94f621903fe..99dec81e7c84 100644
--- a/arch/alpha/include/uapi/asm/socket.h
+++ b/arch/alpha/include/uapi/asm/socket.h

@@ -140,6 +140,8 @@
 #define SO_PASSPIDFD           76
 #define SO_PEERPIDFD           77

+#define SCM_TS_OPT_ID          78
+
 #if !defined(__KERNEL__)

 #if __BITS_PER_LONG == 64

diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index 60ebaed28a4c..bb3dc8feb205 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h

@@ -151,6 +151,8 @@
 #define SO_PASSPIDFD           76
 #define SO_PEERPIDFD           77

+#define SCM_TS_OPT_ID          78
+
 #if !defined(__KERNEL__)

 #if __BITS_PER_LONG == 64

diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
index be264c2b1a11..c3ab3b3289eb 100644
--- a/arch/parisc/include/uapi/asm/socket.h
+++ b/arch/parisc/include/uapi/asm/socket.h

@@ -132,6 +132,8 @@
 #define SO_PASSPIDFD           0x404A
 #define SO_PEERPIDFD           0x404B

+#define SCM_TS_OPT_ID          0x404C
+
 #if !defined(__KERNEL__)

 #if __BITS_PER_LONG == 64

diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index 682da3714686..9b40f0a57fbc 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h

@@ -133,6 +133,8 @@
 #define SO_PASSPIDFD             0x0055
 #define SO_PEERPIDFD             0x0056

+#define SCM_TS_OPT_ID            0x0057
+
 #if !defined(__KERNEL__)

diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 394c3b66065e..f01dd273bea6 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h

@@ -174,6 +174,7 @@ struct inet_cork {
        __s16                   tos;
        char                    priority;
        __u16                   gso_size;
+       u32                     ts_opt_id;
        u64                     transmit_time;
        u32                     mark;
 };

@@ -241,7 +242,8 @@ struct inet_sock {
        struct inet_cork_full   cork;
 };

-#define IPCORK_OPT     1       /* ip-options has been held in ipcork.opt */
+#define IPCORK_OPT             1       /* ip-options has been held in ipcork.opt */
+#define IPCORK_TS_OPT_ID       2       /* ts_opt_id field is valid, overriding sk_tskey */

 enum {
        INET_FLAGS_PKTINFO      = 0,

diff --git a/include/net/sock.h b/include/net/sock.h
index f51d61fab059..c6554ad82961 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h

@@ -952,6 +952,7 @@ enum sock_flags {
 };

 #define SK_FLAGS_TIMESTAMP ((1UL << SOCK_TIMESTAMP) | (1UL << SOCK_TIMESTAMPING_RX_SOFTWARE))
+#define SOCKCM_FLAG_TS_OPT_ID  BIT(31)

 static inline void sock_copy_flags(struct sock *nsk, const struct sock *osk)
 {

@@ -1794,6 +1795,7 @@ struct sockcm_cookie {
        u64 transmit_time;
        u32 mark;
        u32 tsflags;
+       u32 ts_opt_id;
 };

 static inline void sockcm_init(struct sockcm_cookie *sockc,

diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 8ce8a39a1e5f..db3df3e74b01 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h

@@ -135,6 +135,8 @@
 #define SO_PASSPIDFD           76
 #define SO_PEERPIDFD           77

+#define SCM_TS_OPT_ID          78
+
 #if !defined(__KERNEL__)

 #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))

diff --git a/include/uapi/linux/net_tstamp.h b/include/uapi/linux/net_tstamp.h
index a2c66b3d7f0f..1c38536350e7 100644
--- a/include/uapi/linux/net_tstamp.h
+++ b/include/uapi/linux/net_tstamp.h

@@ -38,6 +38,13 @@ enum {
                                 SOF_TIMESTAMPING_LAST
 };

+/*
+ * The highest bit of sk_tsflags is reserved for kernel-internal
+ * SOCKCM_FLAG_TS_OPT_ID. This check is to control that SOF_TIMESTAMPING*
+ * values do not reach this reserved area
+ */
+static_assert(SOF_TIMESTAMPING_LAST != (1 << 31));