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

[David Ahern <dsahern@kernel.org>]

On 2/24/25 12:03 PM, Eric Dumazet wrote:
> 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 {
> }

Also, if a tracepoint is added, inside of tcp_sendmsg_locked would cover
more use cases (see kernel references to it).

We have a patch for a couple years now with a tracepoint inside the

while (msg_data_left(msg)) {
}

loop which is more useful than just entry to sendmsg.