Re: [PATCH bpf-next v3 13/15] libbpf: Support attaching struct_ops to a cgroup

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Mon Jul 6, 2026 at 1:19 PM EDT, Amery Hung wrote:
> From: Martin KaFai Lau <martin.lau@kernel.org>
>
> Add bpf_map__attach_cgroup_opts() to attach a struct_ops map to a cgroup
> through a BPF link.
>
> Also extend struct bpf_prog_query_opts with a type_id field so a
> BPF_STRUCT_OPS query on a cgroup can select the struct_ops type to
> enumerate.
>
> Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
> Signed-off-by: Amery Hung <ameryhung@gmail.com>

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>

> ---
>  tools/lib/bpf/bpf.c      |  2 ++
>  tools/lib/bpf/bpf.h      |  3 +-
>  tools/lib/bpf/libbpf.c   | 64 ++++++++++++++++++++++++++++++++++++++++
>  tools/lib/bpf/libbpf.h   |  3 ++
>  tools/lib/bpf/libbpf.map |  1 +
>  5 files changed, 72 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 96819c082c77..a9de7f107cf7 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -934,6 +934,7 @@ int bpf_link_create(int prog_fd, int target_fd,
>  	case BPF_CGROUP_GETSOCKOPT:
>  	case BPF_CGROUP_SETSOCKOPT:
>  	case BPF_LSM_CGROUP:
> +	case BPF_STRUCT_OPS:
>  		relative_fd = OPTS_GET(opts, cgroup.relative_fd, 0);
>  		relative_id = OPTS_GET(opts, cgroup.relative_id, 0);
>  		if (relative_fd && relative_id)
> @@ -1056,6 +1057,7 @@ int bpf_prog_query_opts(int target, enum bpf_attach_type type,
>  	attr.query.attach_type		= type;
>  	attr.query.query_flags		= OPTS_GET(opts, query_flags, 0);
>  	attr.query.count		= OPTS_GET(opts, count, 0);
> +	attr.query.type_id		= OPTS_GET(opts, type_id, 0);
>  	attr.query.prog_ids		= ptr_to_u64(OPTS_GET(opts, prog_ids, NULL));
>  	attr.query.link_ids		= ptr_to_u64(OPTS_GET(opts, link_ids, NULL));
>  	attr.query.prog_attach_flags	= ptr_to_u64(OPTS_GET(opts, prog_attach_flags, NULL));
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 7534a593edae..490e8cb4ba53 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -637,9 +637,10 @@ struct bpf_prog_query_opts {
>  	__u32 *link_ids;
>  	__u32 *link_attach_flags;
>  	__u64 revision;
> +	__u32 type_id;
>  	size_t :0;
>  };
> -#define bpf_prog_query_opts__last_field revision
> +#define bpf_prog_query_opts__last_field type_id
>  
>  /**
>   * @brief **bpf_prog_query_opts()** queries the BPF programs and BPF links
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 7162146280a8..50a83b9217e4 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -14104,6 +14104,70 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
>  	return &link->link;
>  }
>  
> +struct bpf_link *bpf_map__attach_cgroup_opts(const struct bpf_map *map, int cgroup_fd,
> +					     const struct bpf_cgroup_opts *opts)
> +{
> +	LIBBPF_OPTS(bpf_link_create_opts, link_create_opts);
> +	struct bpf_link_struct_ops *link;
> +	__u32 relative_id, zero = 0;
> +	int err, fd, relative_fd;
> +
> +	if (!OPTS_VALID(opts, bpf_cgroup_opts))
> +		return libbpf_err_ptr(-EINVAL);
> +
> +	if (!bpf_map__is_struct_ops(map)) {
> +		pr_warn("map '%s': can't attach non-struct_ops map\n", map->name);
> +		return libbpf_err_ptr(-EINVAL);
> +	}
> +
> +	if (map->fd < 0) {
> +		pr_warn("map '%s': can't attach BPF map without FD (was it created?)\n", map->name);
> +		return libbpf_err_ptr(-EINVAL);
> +	}
> +
> +	if (!(map->def.map_flags & BPF_F_LINK)) {
> +		pr_warn("map '%s': can't attach to cgroup without BPF_F_LINK\n", map->name);
> +		return libbpf_err_ptr(-EINVAL);
> +	}
> +
> +	relative_id = OPTS_GET(opts, relative_id, 0);
> +	relative_fd = OPTS_GET(opts, relative_fd, 0);
> +
> +	if (relative_fd && relative_id) {
> +		pr_warn("map '%s': relative_fd and relative_id cannot be set at the same time\n",
> +			map->name);
> +		return libbpf_err_ptr(-EINVAL);
> +	}
> +
> +	link_create_opts.cgroup.expected_revision = OPTS_GET(opts, expected_revision, 0);
> +	link_create_opts.cgroup.relative_fd = relative_fd;
> +	link_create_opts.cgroup.relative_id = relative_id;
> +	link_create_opts.flags = OPTS_GET(opts, flags, 0);
> +
> +	link = calloc(1, sizeof(*link));
> +	if (!link)
> +		return libbpf_err_ptr(-ENOMEM);
> +
> +	err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
> +	if (err && err != -EBUSY) {
> +		free(link);
> +		return libbpf_err_ptr(err);
> +	}
> +
> +	link->link.detach = bpf_link__detach_struct_ops;
> +
> +	fd = bpf_link_create(map->fd, cgroup_fd, BPF_STRUCT_OPS, &link_create_opts);
> +	if (fd < 0) {
> +		free(link);
> +		return libbpf_err_ptr(fd);
> +	}
> +
> +	link->link.fd = fd;
> +	link->map_fd = map->fd;
> +
> +	return &link->link;
> +}
> +
>  /*
>   * Swap the back struct_ops of a link with a new struct_ops map.
>   */
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index b965ad571540..0e5f4e9bba41 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -960,6 +960,9 @@ bpf_program__attach_cgroup_opts(const struct bpf_program *prog, int cgroup_fd,
>  struct bpf_map;
>  
>  LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
> +LIBBPF_API struct bpf_link *bpf_map__attach_cgroup_opts(const struct bpf_map *map,
> +							int cgroup_fd,
> +							const struct bpf_cgroup_opts *opts);
>  LIBBPF_API int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map);
>  
>  struct bpf_iter_attach_opts {
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index b731df19ae69..5131fdb979b7 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -461,4 +461,5 @@ LIBBPF_1.8.0 {
>  		bpf_program__attach_tracing_multi;
>  		bpf_program__clone;
>  		btf__new_empty_opts;
> +		bpf_map__attach_cgroup_opts;
>  } LIBBPF_1.7.0;