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Message-ID: <66d0783ca3dc4_3895fa2946a@willemb.c.googlers.com.notmuch>
Date: Thu, 29 Aug 2024 09:31:40 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Vadim Fedorenko <vadfed@...a.com>,
Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
Jakub Kicinski <kuba@...nel.org>,
Willem de Bruijn <willemb@...gle.com>,
Paolo Abeni <pabeni@...hat.com>,
David Ahern <dsahern@...nel.org>
Cc: Vadim Fedorenko <vadfed@...a.com>,
netdev@...r.kernel.org
Subject: Re: [RFC PATCH] net_tstamp: add SCM_TS_OPT_ID to provide OPT_ID in
control message
Vadim Fedorenko wrote:
> SOF_TIMESTAMPING_OPT_ID socket option flag gives a way to correlate TX
> timestamps
+1 on the feature. Few minor points only.
Not a hard requirement, but would be nice if there was a test,
e.g., as a tools/testing/../txtimestamp.c extension.
> and packets sent via socket. Unfortunately, there is no way
> to reliably predict socket timestamp ID value in case of error returned
> by sendmsg [1].
Might be good to copy more context from the discussion to explain why
reliable OPT_ID is infeasible. For UDP, it is as simple as lockless
transmit. For RAW, things like MSG_MORE come into play.
> 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.
> Also, there is no easy way to use 0 as provided ID, so this is value
> treated as invalid.
This is because the code branches on non-zero value in the cookie,
else uses ts_key. Please make this explicit. Or perhaps better, add a
bit in the cookie so that the full 32-bit space can be used.
> [1] https://lore.kernel.org/netdev/CALCETrU0jB+kg0mhV6A8mrHfTE1D1pr1SD_B9Eaa9aDPfgHdtA@mail.gmail.com/
>
> Signed-off-by: Vadim Fedorenko <vadfed@...a.com>
> ---
> include/net/inet_sock.h | 1 +
> include/net/sock.h | 1 +
> include/uapi/asm-generic/socket.h | 2 ++
> net/core/sock.c | 14 ++++++++++++++
> net/ipv4/ip_output.c | 11 +++++++++--
> net/ipv6/ip6_output.c | 11 +++++++++--
> 6 files changed, 36 insertions(+), 4 deletions(-)
>
> diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
> index 394c3b66065e..7e8545311557 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;
> };
Ah there's a hole here. Nice!
> 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/net/core/sock.c b/net/core/sock.c
> index 468b1239606c..918cb6a0dcba 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2859,6 +2859,20 @@ int __sock_cmsg_send(struct sock *sk, struct cmsghdr *cmsg,
> return -EINVAL;
> sockc->transmit_time = get_unaligned((u64 *)CMSG_DATA(cmsg));
> break;
> + case SCM_TS_OPT_ID:
> + /* allow this option for UDP sockets only */
> + if (!sk_is_udp(sk))
> + return -EINVAL;
> + tsflags = READ_ONCE(sk->sk_tsflags);
> + if (!(tsflags & SOF_TIMESTAMPING_OPT_ID))
> + return -EINVAL;
> + if (cmsg->cmsg_len != CMSG_LEN(sizeof(u32)))
> + return -EINVAL;
> + sockc->ts_opt_id = get_unaligned((u32 *)CMSG_DATA(cmsg));
Is the get_unaligned here needed? I don't usually see that on
CMSG_DATA accesses. Even though they are indeed likely to be
unaligned.
> + /* do not allow 0 as packet id for timestamp */
> + if (!sockc->ts_opt_id)
> + return -EINVAL;
> + break;
> /* SCM_RIGHTS and SCM_CREDENTIALS are semantically in SOL_UNIX. */
> case SCM_RIGHTS:
> case SCM_CREDENTIALS:
> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
> index b90d0f78ac80..f1e6695cafd2 100644
> --- a/net/ipv4/ip_output.c
> +++ b/net/ipv4/ip_output.c
> @@ -1050,8 +1050,14 @@ static int __ip_append_data(struct sock *sk,
>
> hold_tskey = cork->tx_flags & SKBTX_ANY_TSTAMP &&
> READ_ONCE(sk->sk_tsflags) & SOF_TIMESTAMPING_OPT_ID;
> - if (hold_tskey)
> - tskey = atomic_inc_return(&sk->sk_tskey) - 1;
> + if (hold_tskey) {
> + if (cork->ts_opt_id) {
> + hold_tskey = false;
> + tskey = cork->ts_opt_id;
> + } else {
> + tskey = atomic_inc_return(&sk->sk_tskey) - 1;
> + }
> + }
>
> /* So, what's going on in the loop below?
> *
> @@ -1324,6 +1330,7 @@ static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
> cork->mark = ipc->sockc.mark;
> cork->priority = ipc->priority;
> cork->transmit_time = ipc->sockc.transmit_time;
> + cork->ts_opt_id = ipc->sockc.ts_opt_id;
> cork->tx_flags = 0;
> sock_tx_timestamp(sk, ipc->sockc.tsflags, &cork->tx_flags);
>
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index f26841f1490f..602064250546 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1401,6 +1401,7 @@ static int ip6_setup_cork(struct sock *sk, struct inet_cork_full *cork,
> cork->base.gso_size = ipc6->gso_size;
> cork->base.tx_flags = 0;
> cork->base.mark = ipc6->sockc.mark;
> + cork->base.ts_opt_id = ipc6->sockc.ts_opt_id;
> sock_tx_timestamp(sk, ipc6->sockc.tsflags, &cork->base.tx_flags);
>
> cork->base.length = 0;
> @@ -1545,8 +1546,14 @@ static int __ip6_append_data(struct sock *sk,
>
> hold_tskey = cork->tx_flags & SKBTX_ANY_TSTAMP &&
> READ_ONCE(sk->sk_tsflags) & SOF_TIMESTAMPING_OPT_ID;
> - if (hold_tskey)
> - tskey = atomic_inc_return(&sk->sk_tskey) - 1;
> + if (hold_tskey) {
> + if (cork->ts_opt_id) {
> + hold_tskey = false;
> + tskey = cork->ts_opt_id;
> + } else {
> + tskey = atomic_inc_return(&sk->sk_tskey) - 1;
> + }
> + }
>
> /*
> * Let's try using as much space as possible.
> --
> 2.43.5
>
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