Re: [PATCH 4/8] bpf: Add bpf_struct_ops_for_each_prog()

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

On Wed May 20, 2026 at 7:50 PM EDT, Tejun Heo wrote:
> Add a helper that walks the member progs of the struct_ops map
> containing a given @kdata vmtable. struct_ops ->reg() callbacks (and
> similar) sometimes need to inspect the loaded BPF programs, e.g. to
> discover maps they reference via prog->aux->used_maps.
>
> The implementation mirrors bpf_struct_ops_id(): container_of @kdata
> to recover the bpf_struct_ops_map, then iterate st_map->links[i]->prog
> for i in [0, funcs_cnt). Same access pattern, no new locking - by the
> time ->reg() fires st_map is fully populated and stable.
>
> A sched_ext follow-up walks the member progs of a cid-form scheduler's
> struct_ops map, reads prog->aux->arena directly, and requires all member
> progs to reference exactly one arena, without requiring the BPF program
> to call a registration kfunc.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>

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

> ---
>  include/linux/bpf.h         |  3 +++
>  kernel/bpf/bpf_struct_ops.c | 36 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 64968ca6db51..5b99d786e98c 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2129,6 +2129,9 @@ int bpf_prog_assoc_struct_ops(struct bpf_prog *prog, struct bpf_map *map);
>  void bpf_prog_disassoc_struct_ops(struct bpf_prog *prog);
>  void *bpf_prog_get_assoc_struct_ops(const struct bpf_prog_aux *aux);
>  u32 bpf_struct_ops_id(const void *kdata);
> +int bpf_struct_ops_for_each_prog(const void *kdata,
> +				 int (*cb)(struct bpf_prog *prog, void *data),
> +				 void *data);
>  
>  #ifdef CONFIG_NET
>  /* Define it here to avoid the use of forward declaration */
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index 05b366b821c3..16aec18ed31b 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -1203,6 +1203,42 @@ u32 bpf_struct_ops_id(const void *kdata)
>  }
>  EXPORT_SYMBOL_GPL(bpf_struct_ops_id);
>  
> +/**
> + * bpf_struct_ops_for_each_prog - Invoke @cb for each member prog
> + * @kdata: kernel-side struct_ops vmtable (the @kdata arg to ->reg/->update/->unreg)
> + * @cb: callback invoked once per member prog; non-zero return stops iteration
> + * @data: opaque argument passed to @cb
> + *
> + * Walks the struct_ops member progs registered on the map containing @kdata.
> + * Intended for use from struct_ops ->reg() callbacks (and similar) that need to
> + * inspect the loaded BPF programs (for example to discover maps they reference
> + * via @prog->aux->used_maps).
> + *
> + * Return 0 if iteration completed, otherwise the first non-zero @cb return.
> + */
> +int bpf_struct_ops_for_each_prog(const void *kdata,
> +				 int (*cb)(struct bpf_prog *prog, void *data),
> +				 void *data)
> +{
> +	struct bpf_struct_ops_value *kvalue;
> +	struct bpf_struct_ops_map *st_map;
> +	u32 i;
> +	int ret;
> +
> +	kvalue = container_of(kdata, struct bpf_struct_ops_value, data);
> +	st_map = container_of(kvalue, struct bpf_struct_ops_map, kvalue);
> +
> +	for (i = 0; i < st_map->funcs_cnt; i++) {
> +		if (!st_map->links[i])
> +			continue;
> +		ret = cb(st_map->links[i]->prog, data);
> +		if (ret)
> +			return ret;
> +	}
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(bpf_struct_ops_for_each_prog);
> +
>  static bool bpf_struct_ops_valid_to_reg(struct bpf_map *map)
>  {
>  	struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;