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Message-ID: <66d5def0ca56_66cf629420@willemb.c.googlers.com.notmuch>
Date: Mon, 02 Sep 2024 11:51:12 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jason Xing <kerneljasonxing@...il.com>,
Vadim Fedorenko <vadfed@...a.com>
Cc: Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
Willem de Bruijn <willemb@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
David Ahern <dsahern@...nel.org>,
netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2 1/2] net_tstamp: add SCM_TS_OPT_ID to provide
OPT_ID in control message
Jason Xing wrote:
> On Mon, Sep 2, 2024 at 9:09 PM Vadim Fedorenko <vadfed@...a.com> wrote:
> >
> > 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. This works fine for UDP
> > sockets only, and explicit check is added to control message parser.
> >
> > [1] https://lore.kernel.org/netdev/CALCETrU0jB+kg0mhV6A8mrHfTE1D1pr1SD_B9Eaa9aDPfgHdtA@mail.gmail.com/
> >
> > Signed-off-by: Vadim Fedorenko <vadfed@...a.com>
> > ---
> > Documentation/networking/timestamping.rst | 14 ++++++++++++++
> > arch/alpha/include/uapi/asm/socket.h | 4 +++-
> > 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 | 1 +
> > include/uapi/asm-generic/socket.h | 2 ++
> > include/uapi/linux/net_tstamp.h | 3 ++-
> > net/core/sock.c | 12 ++++++++++++
> > net/ethtool/common.c | 1 +
> > net/ipv4/ip_output.c | 16 ++++++++++++----
> > net/ipv6/ip6_output.c | 16 ++++++++++++----
> > 13 files changed, 68 insertions(+), 11 deletions(-)
> >
> > diff --git a/Documentation/networking/timestamping.rst b/Documentation/networking/timestamping.rst
> > index 5e93cd71f99f..93b0901e4e8e 100644
> > --- a/Documentation/networking/timestamping.rst
> > +++ b/Documentation/networking/timestamping.rst
> > @@ -193,6 +193,20 @@ SOF_TIMESTAMPING_OPT_ID:
> > among all possibly concurrently outstanding timestamp requests for
> > that socket.
> >
> > + With this option enabled user-space application can provide custom
> > + ID for each message sent via UDP socket with control message with
> > + type set to SCM_TS_OPT_ID::
> > +
> > + struct msghdr *msg;
> > + ...
> > + cmsg = CMSG_FIRSTHDR(msg);
> > + cmsg->cmsg_level = SOL_SOCKET;
> > + cmsg->cmsg_type = SO_TIMESTAMPING;
> > + 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..0698e6662cdf 100644
> > --- a/arch/alpha/include/uapi/asm/socket.h
> > +++ b/arch/alpha/include/uapi/asm/socket.h
> > @@ -10,7 +10,7 @@
> > * Note: we only bother about making the SOL_SOCKET options
> > * same as OSF/1, as that's all that "normal" programs are
> > * likely to set. We don't necessarily want to be binary
> > - * compatible with _everything_.
> > + * compatible with _everything_.
> > */
> > #define SOL_SOCKET 0xffff
> >
> > @@ -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..2161d50cf0fd 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 /* timestmap opt id has been provided in cmsg */
> >
> > enum {
> > INET_FLAGS_PKTINFO = 0,
> > diff --git a/include/net/sock.h b/include/net/sock.h
> > index f51d61fab059..73e21dad5660 100644
> > --- a/include/net/sock.h
> > +++ b/include/net/sock.h
> > @@ -1794,6 +1794,7 @@ 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..e2f145e3f3a1 100644
> > --- a/include/uapi/linux/net_tstamp.h
> > +++ b/include/uapi/linux/net_tstamp.h
> > @@ -32,8 +32,9 @@ enum {
> > SOF_TIMESTAMPING_OPT_TX_SWHW = (1<<14),
> > SOF_TIMESTAMPING_BIND_PHC = (1 << 15),
> > SOF_TIMESTAMPING_OPT_ID_TCP = (1 << 16),
> > + SOF_TIMESTAMPING_OPT_ID_CMSG = (1 << 17),
>
> I'm not sure if the new flag needs to be documented as well? After
> this patch, people may search the key word in the documentation file
> and then find nothing.
>
> If we have this flag here, normally it means we can pass it through
> setsockopt, so is it expected? If it's an exception, I reckon that we
> can forbid passing/setting this option in sock_set_timestamping() and
> document this rule?
Good point, thanks.
It must definitely not be part of SOF_TIMESTAMPING_MASK. My bad for
suggesting without giving it much thought.
The bit is kernel-internal. No need to even mention it in user-facing
documentation. But anyone reading net_tstamp.h might wonder what it
does.
It should not even be in a UAPI header, but in an internal one.
Probably include/net/sock.h, near SK_FLAGS_TIMESTAMP.
Maybe we can reserve bit 31 in u32 sk_tsflags. And if we ever have
to double that flag size, it can move up to 63, as it is not UAPI in
any way. This is a workaround to having a separate flags field in
sockcm_cookie.
And have a BUILD_BUG_ON if SOF_TIMESTAMPING_LAST reaches this reserved
region.
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