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

[Taeung Song <treeze.taeung@gmail.com>]

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 ?

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.

> unconditionally print warnings is not great..
> 

OK, need to change that, will send v2.

Thanks,
Taeung

>> For example, when a 'cgroup' section name of a BPF program is used,
>>
>> Before:
>>
>>      $ bpftool prog load bpf-prog.o /sys/fs/bpf/prog1
>>      Error: failed to guess program type based on section name cgroup
>>
>> After:
>>
>>      libbpf: failed to guess program type based on section name 'cgroup'
>>      libbpf: possible section(type) names are: socket kprobe/ kretprobe/ classifier action tracepoint/ raw_tracepoint/ xdp perf_event lwt_in lwt_out lwt_xmit lwt_seg6local cgroup_skb/ingress cgroup_skb/egress cgroup/skb cgroup/sock cgroup/post_bind4 cgroup/post_bind6 cgroup/dev sockops sk_skb/stream_parser sk_skb/stream_verdict sk_skb sk_msg lirc_mode2 flow_dissector cgroup/bind4 cgroup/bind6 cgroup/connect4 cgroup/connect6 cgroup/sendmsg4 cgroup/sendmsg6
>>
>> Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
>> Cc: Andrey Ignatov <rdna@fb.com>
>> Signed-off-by: Taeung Song <treeze.taeung@gmail.com>