Re: [PATCH bpf-next v3 03/15] bpf: Add bpf_struct_ops accessor helpers

["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 the helper functions bpf_struct_ops_map_kdata() and
> bpf_struct_ops_map_cfi_stubs() in bpf_struct_ops.c. They will be called
> from cgroup.c in the upcoming patch to create a struct_ops to cgroup
> attachment link.
>
> bpf_struct_ops_valid_to_reg() is also exposed for the upcoming caller
> in cgroup.c.
>
> The link update validation is also refactored into a new function
> bpf_struct_ops_link_update_check() such that it can be reused by the
> caller in cgroup.c in the upcoming patch.
>
> 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>

> ---
>  include/linux/bpf.h         | 28 ++++++++++++++++++++
>  kernel/bpf/bpf_struct_ops.c | 53 +++++++++++++++++++++++++++----------
>  2 files changed, 67 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 7ac8873839f4..047ffc029666 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2252,6 +2252,12 @@ 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);
> +void *bpf_struct_ops_map_kdata(struct bpf_map *map);
> +u32 bpf_struct_ops_kdata_map_id(void *kdata);
> +void *bpf_struct_ops_map_cfi_stubs(struct bpf_map *map);
> +bool bpf_struct_ops_valid_to_reg(struct bpf_map *map);
> +int bpf_struct_ops_link_update_check(struct bpf_map *new_map, struct bpf_map *old_map,
> +				     struct bpf_map *expected_old_map);
>  
>  #ifdef CONFIG_NET
>  /* Define it here to avoid the use of forward declaration */
> @@ -2316,6 +2322,28 @@ static inline void bpf_map_struct_ops_info_fill(struct bpf_map_info *info, struc
>  static inline void bpf_struct_ops_desc_release(struct bpf_struct_ops_desc *st_ops_desc)
>  {
>  }
> +static inline void *bpf_struct_ops_map_kdata(struct bpf_map *map)
> +{
> +	return NULL;
> +}
> +static inline u32 bpf_struct_ops_kdata_map_id(void *kdata)
> +{
> +	return 0;
> +}
> +static inline void *bpf_struct_ops_map_cfi_stubs(struct bpf_map *map)
> +{
> +	return NULL;
> +}
> +static inline bool bpf_struct_ops_valid_to_reg(struct bpf_map *map)
> +{
> +	return false;
> +}
> +static inline int bpf_struct_ops_link_update_check(struct bpf_map *new_map,
> +						   struct bpf_map *old_map,
> +						   struct bpf_map *expected_old_map)
> +{
> +	return -EOPNOTSUPP;
> +}
>  
>  #endif
>  
> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
> index c422ce41873e..3d650a7e9f68 100644
> --- a/kernel/bpf/bpf_struct_ops.c
> +++ b/kernel/bpf/bpf_struct_ops.c
> @@ -1236,7 +1236,23 @@ int bpf_struct_ops_for_each_prog(const void *kdata,
>  }
>  EXPORT_SYMBOL_GPL(bpf_struct_ops_for_each_prog);
>  
> -static bool bpf_struct_ops_valid_to_reg(struct bpf_map *map)
> +void *bpf_struct_ops_map_kdata(struct bpf_map *map)
> +{
> +	struct bpf_struct_ops_map *st_map;
> +
> +	st_map = container_of(map, struct bpf_struct_ops_map, map);
> +	return st_map->kvalue.data;
> +}
> +
> +void *bpf_struct_ops_map_cfi_stubs(struct bpf_map *map)
> +{
> +	struct bpf_struct_ops_map *st_map;
> +
> +	st_map = container_of(map, struct bpf_struct_ops_map, map);
> +	return st_map->st_ops_desc->st_ops->cfi_stubs;
> +}
> +
> +bool bpf_struct_ops_valid_to_reg(struct bpf_map *map)
>  {
>  	struct bpf_struct_ops_map *st_map = (struct bpf_struct_ops_map *)map;
>  
> @@ -1289,6 +1305,26 @@ static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link,
>  	return 0;
>  }
>  
> +int bpf_struct_ops_link_update_check(struct bpf_map *new_map,
> +				     struct bpf_map *old_map,
> +				     struct bpf_map *expected_old_map)
> +{
> +	struct bpf_struct_ops_map *st_map, *old_st_map;
> +
> +	if (!old_map)
> +		return -ENOLINK;
> +	if (expected_old_map && old_map != expected_old_map)
> +		return -EPERM;
> +
> +	st_map = container_of(new_map, struct bpf_struct_ops_map, map);
> +	old_st_map = container_of(old_map, struct bpf_struct_ops_map, map);
> +	/* The new and old struct_ops must be the same type. */
> +	if (st_map->st_ops_desc != old_st_map->st_ops_desc)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
>  static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map *new_map,
>  					  struct bpf_map *expected_old_map)
>  {
> @@ -1307,23 +1343,12 @@ static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map
>  		return -EOPNOTSUPP;
>  
>  	mutex_lock(&update_mutex);
> -
>  	old_map = st_link->map;
> -	if (!old_map) {
> -		err = -ENOLINK;
> -		goto err_out;
> -	}
> -	if (expected_old_map && old_map != expected_old_map) {
> -		err = -EPERM;
> +	err = bpf_struct_ops_link_update_check(new_map, old_map, expected_old_map);
> +	if (err)
>  		goto err_out;
> -	}
>  
>  	old_st_map = container_of(old_map, struct bpf_struct_ops_map, map);
> -	/* The new and old struct_ops must be the same type. */
> -	if (st_map->st_ops_desc != old_st_map->st_ops_desc) {
> -		err = -EINVAL;
> -		goto err_out;
> -	}
>  
>  	err = st_map->st_ops_desc->st_ops->update(st_map->kvalue.data, old_st_map->kvalue.data, link);
>  	if (err)