netdev - Re: [PATCH bpf-next] libbpf: Show possible section(type) names on when failed to guess a type

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Message-ID: <20181219182209.439cbf5a@cakuba.netronome.com>
Date:   Wed, 19 Dec 2018 18:22:09 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Taeung Song <treeze.taeung@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org,
        Andrey Ignatov <rdna@...com>
Subject: Re: [PATCH bpf-next] libbpf: Show possible section(type) names on
 when failed to guess a type

On Thu, 20 Dec 2018 09:47:12 +0900, Taeung Song wrote:
> On 12/20/18 3:52 AM, Jakub Kicinski wrote:
> > On Wed, 19 Dec 2018 17:52:40 +0900, Taeung Song wrote:  
> >> We need to let users check their wrong section name
> >> with proper section names when failed to get proper type from it.
> >> Because there is no knowing what kind of section name can be used.  
> > 
> > # bpftool prog help
> > Usage: bpftool prog { show | list } [PROG]
> > 	[...]
> > 	TYPE := { socket | kprobe | kretprobe | classifier | action |
> >                   tracepoint | raw_tracepoint | xdp | perf_event | cgroup/skb |
> >                   cgroup/sock | cgroup/dev | lwt_in | lwt_out | lwt_xmit |
> >                   lwt_seg6local | sockops | sk_skb | sk_msg | lirc_mode2 |
> >                   sk_reuseport | flow_dissector |
> >                   cgroup/bind4 | cgroup/bind6 | cgroup/post_bind4 |
> >                   cgroup/post_bind6 | cgroup/connect4 | cgroup/connect6 |
> >                   cgroup/sendmsg4 | cgroup/sendmsg6 }
> >         ATTACH_TYPE := { msg_verdict | skb_verdict | skb_parse |
> >                          flow_dissector }
> >         OPTIONS := { {-j|--json} [{-p|--pretty}] | {-f|--bpffs} |
> > 	            {-m|--mapcompat} | {-n|--nomount} }
> > 
> > Also in man bpftool-prog.
> > 
> > Perhaps we could just point users to that info?  IMHO having libraries  
> 
> Right, I think when users used wrong section names
> we need to let them realize libbpf guess prog/attach types from given 
> section names because users who are unfamiliar with BPF programming
> mightn't even know that, right ?

The error messages says:

	failed to guess program type based on section name X

I'm not good with user friendly error messages, unfortunately but to me
it clearly state we tried to guess the type based on section name..

Perhaps we could improve it?  Say "ELF section name"?  Take the section
name into single quotes?  Not sure..

> And how about a function that return supported section names ?
> I think it can be used for the 'TYPE'/'ATTACH_TYPE' help message
> because it is just a string and couldn't have latest types.

The man page has to be updated manually, anyway, no?  I don't have a
strong opinion as long as formatting doesn't suffer.