Re: [PATCH net-next] trace: tcp: Add tracepoint for tcp_sendmsg()

Yonghong Song
2025-02-24T19:13:09Z

> ________________________________________
>
> On Mon, Feb 24, 2025 at 7:24 PM Breno Leitao <leitao@debian.org> wrote:
>>
>> Add a lightweight tracepoint to monitor TCP sendmsg operations, enabling
>> the tracing of TCP messages being sent.
>>
>> Meta has been using BPF programs to monitor this function for years,
>> indicating significant interest in observing this important
>> functionality. Adding a proper tracepoint provides a stable API for all
>> users who need visibility into TCP message transmission.
>>
>> The implementation uses DECLARE_TRACE instead of TRACE_EVENT to avoid
>> creating unnecessary trace event infrastructure and tracefs exports,
>> keeping the implementation minimal while stabilizing the API.
>>
>> Given that this patch creates a rawtracepoint, you could hook into it
>> using regular tooling, like bpftrace, using regular rawtracepoint
>> infrastructure, such as:
>>
>> rawtracepoint:tcp_sendmsg_tp {
>> ....
>> }
>
> I would expect tcp_sendmsg() being stable enough ?
>
> kprobe:tcp_sendmsg {
> }

In LTO mode, tcp_sendmsg could be inlined cross files. For example,

net/ipv4/tcp.c:
int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
net/ipv4/tcp_bpf.c:
...
return tcp_sendmsg(sk, msg, size);
net/ipv6/af_inet6.c:
...
return INDIRECT_CALL_2(prot->sendmsg, tcp_sendmsg, udpv6_sendmsg, ...)

And this does happen in our production environment.