Re: [PATCH v4 bpf-next 2/9] libbpf: introduce concept of bpf_link

[Yonghong Song <yhs@fb.com>]

On 6/28/19 8:48 PM, Andrii Nakryiko wrote:
> bpf_link is and abstraction of an association of a BPF program and one

"is and" => "is an".

> of many possible BPF attachment points (hooks). This allows to have
> uniform interface for detaching BPF programs regardless of the nature of
> link and how it was created. Details of creation and setting up of
> a specific bpf_link is handled by corresponding attachment methods
> (bpf_program__attach_xxx) added in subsequent commits. Once successfully
> created, bpf_link has to be eventually destroyed with
> bpf_link__destroy(), at which point BPF program is disassociated from
> a hook and all the relevant resources are freed.
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> Acked-by: Song Liu <songliubraving@fb.com>
> ---
>   tools/lib/bpf/libbpf.c   | 17 +++++++++++++++++
>   tools/lib/bpf/libbpf.h   |  4 ++++
>   tools/lib/bpf/libbpf.map |  3 ++-
>   3 files changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6e6ebef11ba3..455795e6f8af 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -3941,6 +3941,23 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
>   	return 0;
>   }
>   
> +struct bpf_link {
> +	int (*destroy)(struct bpf_link *link);
> +};
> +
> +int bpf_link__destroy(struct bpf_link *link)
> +{
> +	int err;
> +
> +	if (!link)
> +		return 0;
> +
> +	err = link->destroy(link);
> +	free(link);
> +
> +	return err;
> +}
> +
>   enum bpf_perf_event_ret
>   bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
>   			   void **copy_mem, size_t *copy_size,
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index d639f47e3110..5082a5ebb0c2 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -165,6 +165,10 @@ LIBBPF_API int bpf_program__pin(struct bpf_program *prog, const char *path);
>   LIBBPF_API int bpf_program__unpin(struct bpf_program *prog, const char *path);
>   LIBBPF_API void bpf_program__unload(struct bpf_program *prog);
>   
> +struct bpf_link;
> +
> +LIBBPF_API int bpf_link__destroy(struct bpf_link *link);
> +
>   struct bpf_insn;
>   
>   /*
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 2c6d835620d2..3cde850fc8da 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -167,10 +167,11 @@ LIBBPF_0.0.3 {
>   
>   LIBBPF_0.0.4 {
>   	global:
> +		bpf_link__destroy;
> +		bpf_object__load_xattr;
>   		btf_dump__dump_type;
>   		btf_dump__free;
>   		btf_dump__new;
>   		btf__parse_elf;
> -		bpf_object__load_xattr;
>   		libbpf_num_possible_cpus;
>   } LIBBPF_0.0.3;
>