netdev - Re: [Patch net-next 02/13] ipv4: introduce tracepoint trace_ip_queue

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Date:   Wed, 11 Aug 2021 16:08:27 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Qitao Xu <qitao.xu@...edance.com>,
        Cong Wang <cong.wang@...edance.com>, bpf <bpf@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [Patch net-next 02/13] ipv4: introduce tracepoint
 trace_ip_queue_xmit()

On Wed, Aug 11, 2021 at 03:48:36PM -0700, Cong Wang wrote:
> On Wed, Aug 11, 2021 at 2:23 PM Martin KaFai Lau <kafai@...com> wrote:
> > Instead of adding tracepoints, the bpf fexit prog can be used here and
> > the bpf prog will have the sk, skb, and ret available (example in fexit_test.c).
> > Some tracepoints in this set can also be done with bpf fentry/fexit.
> > Does bpf fentry/fexit work for your use case?
> 
> Well, kprobe works too in this perspective. The problem with kprobe
> or fexit is that there is no guarantee the function still exists in kernel
> during iteration. Kernel is free to delete or rename it. With tracepoint,
> even if ip_queue_xmit() were renamed, the same tracepoint must
> remain in the kernel.
Some of the function names are hardly changed.  Considering it is
not always cost free based on another thread, this is not a strong
enough reason to add so many tracepoints while other options
are available.