linux-kernel - Re: bpf_errno. Was: [PATCH RFC bpf-next 1/3] bpf: report probe fault to BPF stderr

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Message-ID: <CAP01T75DqdVHgfD5e4ZcizZLrh7+VOv4cmNyZ2YFbFJE3f0Ttw@mail.gmail.com>
Date: Wed, 8 Oct 2025 22:59:35 +0200
From: Kumar Kartikeya Dwivedi <memxor@...il.com>
To: Eduard Zingerman <eddyz87@...il.com>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Leon Hwang <hffilwlqm@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Menglong Dong <menglong.dong@...ux.dev>, 
	Menglong Dong <menglong8.dong@...il.com>, Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>, jiang.biao@...ux.dev
Subject: Re: bpf_errno. Was: [PATCH RFC bpf-next 1/3] bpf: report probe fault
 to BPF stderr

On Wed, 8 Oct 2025 at 22:30, Eduard Zingerman <eddyz87@...il.com> wrote:
>
> On Wed, 2025-10-08 at 22:08 +0200, Kumar Kartikeya Dwivedi wrote:
>
> [...]
>
> > Since we're piling on ideas, one of the other things that I think
> > could be useful in general (and maybe should be done orthogonally to
> > bpf_errno)
> > is making some empty nop function and making it not traceable reliably
>                                                   ^^^^^^^^^^^^^
>                                    You mean traceable, right?
>                    So that user attaches a bpf program to it,
>                   and debugs bpf programs using bpf programs?

Yeah, sorry, typo.

>
> > across arches and invoke it in the bpf exception handler.
> > Then if we expose prog_stream_dump_stack() as a kfunc (should be
> > trivial), the user can write anything to stderr that is relevant to
> > get more information on the fault.
> >
> > It is then up to the user to decide the rate of messages for such
> > faults etc. and get more information if needed.