On Tue, Feb 14, 2023 at 2:17 PM Kui-Feng Lee <kuifeng@xxxxxxxx> wrote:
>
> Introduce bpf_link__update_struct_ops(), which will allow you to
> effortlessly transition the struct_ops map of any given bpf_link into
> an alternative.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@xxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 35 +++++++++++++++++++++++++++++++++++
> tools/lib/bpf/libbpf.h | 1 +
> tools/lib/bpf/libbpf.map | 1 +
> 3 files changed, 37 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 1eff6a03ddd9..6f7c72e312d4 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -11524,6 +11524,41 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
> return &link->link;
> }
>
> +/*
> + * Swap the back struct_ops of a link with a new struct_ops map.
> + */
> +int bpf_link__update_struct_ops(struct bpf_link *link, const struct bpf_map *map)
we have bpf_link__update_program(), and so the generic counterpart for
map-based links would be bpf_link__update_map(). Let's call it that.
And it shouldn't probably assume so much struct_ops specific things.
> +{
> + struct bpf_link_struct_ops_map *st_ops_link;
> + int err, fd;
> +
> + if (!bpf_map__is_struct_ops(map) || map->fd == -1)
> + return -EINVAL;
> +
> + /* Ensure the type of a link is correct */
> + if (link->detach != bpf_link__detach_struct_ops)
> + return -EINVAL;
> +
> + err = bpf_map__update_vdata(map);
it's a bit weird we do this at attach time, not when bpf_map is
actually instantiated. Should we move this map contents initialization
to bpf_object__load() phase? Same for bpf_map__attach_struct_ops().
What do we lose by doing it after all the BPF programs are loaded in
load phase?
> + if (err) {
> + err = -errno;
> + free(link);
> + return err;
> + }
> +
> + fd = bpf_link_update(link->fd, map->fd, NULL);
> + if (fd < 0) {
> + err = -errno;
> + free(link);
> + return err;
> + }
> +
> + st_ops_link = container_of(link, struct bpf_link_struct_ops_map, link);
> + st_ops_link->map_fd = map->fd;
> +
> + return 0;
> +}
> +
> typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
> void *private_data);
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 2efd80f6f7b9..dd25cd6759d4 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -695,6 +695,7 @@ bpf_program__attach_freplace(const struct bpf_program *prog,
> struct bpf_map;
>
> LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
> +LIBBPF_API int bpf_link__update_struct_ops(struct bpf_link *link, const struct bpf_map *map);
let's rename to bpf_link__update_map() and put it next to
bpf_link__update_program() in libbpf.h
>
> struct bpf_iter_attach_opts {
> size_t sz; /* size of this struct for forward/backward compatibility */
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 11c36a3c1a9f..ca6993c744b6 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -373,6 +373,7 @@ LIBBPF_1.1.0 {
> global:
> bpf_btf_get_fd_by_id_opts;
> bpf_link_get_fd_by_id_opts;
> + bpf_link__update_struct_ops;
> bpf_map_get_fd_by_id_opts;
> bpf_prog_get_fd_by_id_opts;
> user_ring_buffer__discard;
we are in LIBBPF_1.2.0 already, please move
> --
> 2.30.2
>
