netdev - Re: [PATCH v3 bpf-next 0/3] Convert BPF UAPI constants into enum values

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Date:   Wed, 4 Mar 2020 16:21:31 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Andrii Nakryiko <andriin@...com>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, ast@...com
Cc:     andrii.nakryiko@...il.com, kernel-team@...com
Subject: Re: [PATCH v3 bpf-next 0/3] Convert BPF UAPI constants into enum
 values

On 3/3/20 1:32 AM, Andrii Nakryiko wrote:
> Convert BPF-related UAPI constants, currently defined as #define macro, into
> anonymous enums. This has no difference in terms of usage of such constants in
> C code (they are still could be used in all the compile-time contexts that
> `#define`s can), but they are recorded as part of DWARF type info, and
> subsequently get recorded as part of kernel's BTF type info. This allows those
> constants to be emitted as part of vmlinux.h auto-generated header file and be
> used from BPF programs. Which is especially convenient for all kinds of BPF
> helper flags and makes CO-RE BPF programs nicer to write.
> 
> libbpf's btf_dump logic currently assumes enum values are signed 32-bit
> values, but that doesn't match a typical case, so switch it to emit unsigned
> values. Once BTF encoding of BTF_KIND_ENUM is extended to capture signedness
> properly, this will be made more flexible.
> 
> As an immediate validation of the approach, runqslower's copy of
> BPF_F_CURRENT_CPU #define is dropped in favor of its enum variant from
> vmlinux.h.
> 
> v2->v3:
> - convert only constants usable from BPF programs (BPF helper flags, map
>    create flags, etc) (Alexei);
> 
> v1->v2:
> - fix up btf_dump test to use max 32-bit unsigned value instead of negative one.
> 
> 
> Andrii Nakryiko (3):
>    bpf: switch BPF UAPI #define constants used from BPF program side to
>      enums
>    libbpf: assume unsigned values for BTF_KIND_ENUM
>    tools/runqslower: drop copy/pasted BPF_F_CURRENT_CPU definiton
> 
>   include/uapi/linux/bpf.h                      | 175 ++++++++++-------
>   tools/bpf/runqslower/runqslower.bpf.c         |   3 -
>   tools/include/uapi/linux/bpf.h                | 177 +++++++++++-------
>   tools/lib/bpf/btf_dump.c                      |   8 +-
>   .../bpf/progs/btf_dump_test_case_syntax.c     |   2 +-
>   5 files changed, 224 insertions(+), 141 deletions(-)
> 

Applied, thanks!