Re: [PATCH bpf-next 2/3] libbpf: make global data internal arrays mmap()-able, if possible

[Song Liu <songliubraving@fb.com>]

> On Nov 7, 2019, at 8:20 PM, Andrii Nakryiko <andriin@fb.com> wrote:
> 
> Add detection of BPF_F_MMAPABLE flag support for arrays and add it as an extra
> flag to internal global data maps, if supported by kernel. This allows users
> to memory-map global data and use it without BPF map operations, greatly
> simplifying user experience.
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Acked-by: Song Liu <songliubraving@fb.com>

With nit below. 

> ---
> tools/lib/bpf/libbpf.c | 31 +++++++++++++++++++++++++++++--
> 1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index fde6cb3e5d41..73607a31a068 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -142,6 +142,8 @@ struct bpf_capabilities {
> 	__u32 btf_func:1;
> 	/* BTF_KIND_VAR and BTF_KIND_DATASEC support */
> 	__u32 btf_datasec:1;
> +	/* BPF_F_MMAPABLE is supported for arrays */
> +	__u32 array_mmap:1;
> };
> 
> /*
> @@ -855,8 +857,6 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
> 		pr_warn("failed to alloc map name\n");
> 		return -ENOMEM;
> 	}
> -	pr_debug("map '%s' (global data): at sec_idx %d, offset %zu.\n",
> -		 map_name, map->sec_idx, map->sec_offset);
> 
> 	def = &map->def;
> 	def->type = BPF_MAP_TYPE_ARRAY;
> @@ -864,6 +864,12 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
> 	def->value_size = data->d_size;
> 	def->max_entries = 1;
> 	def->map_flags = type == LIBBPF_MAP_RODATA ? BPF_F_RDONLY_PROG : 0;
> +	if (obj->caps.array_mmap)
> +		def->map_flags |= BPF_F_MMAPABLE;
> +
> +	pr_debug("map '%s' (global data): at sec_idx %d, offset %zu, flags %u.\n",

nit: Better print flags as %x.