Re: [PATCHES 0/2] Introduce --btf_features=+extra_features syntax

[Daniel Xu <dxu@dxuuu.xyz>]

Hi Arnaldo,

On Fri, Apr 19, 2024 at 05:57:43PM -0300, Arnaldo Carvalho de Melo wrote:
> Hi,
> 
> 	Please take a look if you agree this is a more compact, less
> confusing way of asking for the set of standard BTF features + some
> extra features such as 'reproducible_build'.
> 
> 	We have this in perf, for things like:
> 
> ⬢[acme@toolbox pahole]$ perf report -h -F 
> 
>  Usage: perf report [<options>]
> 
>     -F, --fields <key[,keys...]>
>                           output field(s): overhead period sample  overhead overhead_sys
>                           overhead_us overhead_guest_sys overhead_guest_us overhead_children
>                           sample period weight1 weight2 weight3 ins_lat retire_lat
>                           p_stage_cyc pid comm dso symbol parent cpu socket
>                           srcline srcfile local_weight weight transaction trace
>                           symbol_size dso_size cgroup cgroup_id ipc_null time
>                           code_page_size local_ins_lat ins_lat local_p_stage_cyc
>                           p_stage_cyc addr local_retire_lat retire_lat simd
>                           type typeoff symoff dso_from dso_to symbol_from symbol_to
>                           mispredict abort in_tx cycles srcline_from srcline_to
>                           ipc_lbr addr_from addr_to symbol_daddr dso_daddr locked
>                           tlb mem snoop dcacheline symbol_iaddr phys_daddr data_page_size
>                           blocked
> 
> ⬢[acme@toolbox pahole]$
> 
> From the 'perf report' man page for '-F':
> 
>         If the keys starts with a prefix '+', then it will append the specified
>         field(s) to the default field order. For example: perf report -F +period,sample.

I think for perf it makes sense to have compact representation b/c
folks might be doing a lot of ad-hoc work. But encoding BTF seems more
like a write-once, read mostly. So having `+` notation doesn't feel like
it'd help that much.

As someone who's not seen that style of syntax before, it's not
immediately obvious what it does. But seeing `all`, I have a pretty
good idea.

[..]

Thanks,
Daniel