netdev - Re: [PATCH bpf-next v8 04/11] bpf: support fsession for bpf_session_is

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Message-ID: <CADxym3YkfSju-mcLSA5_44e-rdQ935Pt_sv75M_BGm3RiDcq2w@mail.gmail.com>
Date: Sat, 10 Jan 2026 12:04:11 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: Menglong Dong <menglong.dong@...ux.dev>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Andrii Nakryiko <andrii@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, jiang.biao@...ux.dev, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, X86 ML <x86@...nel.org>, 
	"H. Peter Anvin" <hpa@...or.com>, bpf <bpf@...r.kernel.org>, 
	Network Development <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v8 04/11] bpf: support fsession for bpf_session_is_return

On Sat, Jan 10, 2026 at 11:38 AM Menglong Dong <menglong.dong@...ux.dev> wrote:
>
> On 2026/1/10 10:40, Alexei Starovoitov wrote:
> > On Wed, Jan 7, 2026 at 6:25 PM Menglong Dong <menglong8.dong@...il.com> wrote:
> > >
> > > +       } else if (func_id == special_kfunc_list[KF_bpf_session_is_return]) {
> > > +               if (prog->expected_attach_type == BPF_TRACE_FSESSION)
> > > +                       addr = (unsigned long)bpf_fsession_is_return;
> >
> > ...
> >
> > > +bool bpf_fsession_is_return(void *ctx)
> > > +{
> > > +       /* This helper call is inlined by verifier. */
> > > +       return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_RETURN));
> > > +}
> > > +
> >
> > Why do this specialization and introduce a global function
> > that will never be called, since it will be inlined anyway?
>
> Ah, the specialization and the definition of the global function
> is not unnecessary. I thought that it's kinda fallback solution
      ^
typo: is not necessary

> that we define the function even if it is inlined by the verifier.
>
> >
> > Remove the first hunk and make the 2nd a comment instead of a real function?
>
> Agree. So it will be:
>
> +static bool bpf_fsession_is_return(void *ctx)
> +{
> +       /* This helper call is implemented and inlined by the verifier, and the logic is:
> +         *   return !!(((u64 *)ctx)[-1] & (1 << BPF_TRAMP_M_IS_RETURN));
> +         */
> +        return false;
> +}
>
> >
> >
>
>
>
>