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Message-ID: <66d627439edbd_71ed729422@willemb.c.googlers.com.notmuch>
Date: Mon, 02 Sep 2024 16:59:47 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: 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,
Jason Xing <kerneljasonxing@...il.com>
Subject: Re: [PATCH net-next v2 1/2] net_tstamp: add SCM_TS_OPT_ID to provide
OPT_ID in control message
Vadim Fedorenko wrote:
> On 02/09/2024 16:51, Willem de Bruijn wrote:
> > 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.
>
> Yeah, I was also thinking of it not being UAPI, that's why I tried to
> avoid it in my RFC using 0 as a reserved value. Do you think
> SK_FLAGS_CMSG_TS_OPT_ID is good naming for it?
It's relevant only to sockcm_cookie, so maybe SOCKCM_FLAG_TS_OPT_ID?
One day we'll need another sockcm_cookie flag, we'll grow it to add a
real flags field and can get rid of this hack.
The struct is used embedded in ipcm_cookie and ipcm6_cookie, which
would grow as a result.
It is also simply stack allocated in cases like performance sensitive
tcp_sendmsg_locked. Here, the main cost is a slightly more expensive
zeroing in sockcm_init.
For now, I think we should just stick with using the highest bit in
sockcm.tsflags.
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