netdev - Re: [PATCH bpf-next v9 01/11] bpf: add fsession support

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Message-ID: <2815339.mvXUDI8C0e@7940hx>
Date: Thu, 15 Jan 2026 10:05:11 +0800
From: Menglong Dong <menglong.dong@...ux.dev>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Menglong Dong <menglong8.dong@...il.com>, ast@...nel.org,
 andrii@...nel.org, daniel@...earbox.net, martin.lau@...ux.dev,
 eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, davem@...emloft.net, dsahern@...nel.org,
 tglx@...utronix.de, mingo@...hat.com, jiang.biao@...ux.dev, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 bpf@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v9 01/11] bpf: add fsession support

On 2026/1/15 02:56 Andrii Nakryiko <andrii.nakryiko@...il.com> write:
> On Tue, Jan 13, 2026 at 6:11 PM Menglong Dong <menglong.dong@...ux.dev> wrote:
> >
> > On 2026/1/14 09:22 Andrii Nakryiko <andrii.nakryiko@...il.com> write:
> > > On Sat, Jan 10, 2026 at 6:11 AM Menglong Dong <menglong8.dong@...il.com> wrote:
> > > >
> > > > The fsession is something that similar to kprobe session. It allow to
> > > > attach a single BPF program to both the entry and the exit of the target
> > > > functions.
> > > >
> > [...]
> > > > --- a/kernel/bpf/btf.c
> > > > +++ b/kernel/bpf/btf.c
> > > > @@ -6107,6 +6107,7 @@ static int btf_validate_prog_ctx_type(struct bpf_verifier_log *log, const struct
> > > >                 case BPF_TRACE_FENTRY:
> > > >                 case BPF_TRACE_FEXIT:
> > > >                 case BPF_MODIFY_RETURN:
> > > > +               case BPF_TRACE_FSESSION:
> > > >                         /* allow u64* as ctx */
> > > >                         if (btf_is_int(t) && t->size == 8)
> > > >                                 return 0;
> > > > @@ -6704,6 +6705,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
> > > >                         fallthrough;
> > > >                 case BPF_LSM_CGROUP:
> > > >                 case BPF_TRACE_FEXIT:
> > > > +               case BPF_TRACE_FSESSION:
> > >
> > > According to the comment below we make this exception due to LSM.
> > > FSESSION won't be using FSESSION programs, no? So this is not
> > > necessary?
> >
> > The comment describe the LSM case here, but the code
> > here is not only for LSM. It is also for FEXIT, which makes
> > sure that we can get the return value with "ctx[nr_args]".
> > So I think we still need it here, as we need to access the
> > return value with "ctx[nr_args]" too.
> 
> please update the comment then as well

ACK

> 
> >
> > >