Re: [PATCH bpf-next v1 1/8] libbpf: allow version suffixes (___smth) for struct_ops types

[David Vernet <void@manifault.com>]

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On Tue, Feb 27, 2024 at 10:45:49PM +0200, Eduard Zingerman wrote:
> E.g. allow the following struct_ops definitions:
> 
>     struct bpf_testmod_ops___v1 { int (*test)(void); };
>     struct bpf_testmod_ops___v2 { int (*test)(void); };
> 
>     SEC(".struct_ops.link")
>     struct bpf_testmod_ops___v1 a = { .test = ... }
>     SEC(".struct_ops.link")
>     struct bpf_testmod_ops___v2 b = { .test = ... }
> 
> Where both bpf_testmod_ops__v1 and bpf_testmod_ops__v2 would be
> resolved as 'struct bpf_testmod_ops' from kernel BTF.
> 
> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>

Acked-by: David Vernet <void@manifault.com>

Modulo the leak pointed out by Kui-Feng in another thread. It would be nice if
we could just do this on the stack, but I guess there's no static max size for
a tname.

> ---
>  tools/lib/bpf/libbpf.c | 22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 01f407591a92..abe663927013 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -948,7 +948,7 @@ static int find_btf_by_prefix_kind(const struct btf *btf, const char *prefix,
>  				   const char *name, __u32 kind);
>  
>  static int
> -find_struct_ops_kern_types(struct bpf_object *obj, const char *tname,
> +find_struct_ops_kern_types(struct bpf_object *obj, const char *tname_raw,
>  			   struct module_btf **mod_btf,
>  			   const struct btf_type **type, __u32 *type_id,
>  			   const struct btf_type **vtype, __u32 *vtype_id,
> @@ -957,15 +957,21 @@ find_struct_ops_kern_types(struct bpf_object *obj, const char *tname,
>  	const struct btf_type *kern_type, *kern_vtype;
>  	const struct btf_member *kern_data_member;
>  	struct btf *btf;
> -	__s32 kern_vtype_id, kern_type_id;
> +	__s32 kern_vtype_id, kern_type_id, err;
> +	char *tname;
>  	__u32 i;
>  
> +	tname = strndup(tname_raw, bpf_core_essential_name_len(tname_raw));
> +	if (!tname)
> +		return -ENOMEM;
> +
>  	kern_type_id = find_ksym_btf_id(obj, tname, BTF_KIND_STRUCT,
>  					&btf, mod_btf);
>  	if (kern_type_id < 0) {
>  		pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n",
>  			tname);
> -		return kern_type_id;
> +		err = kern_type_id;
> +		goto err_out;
>  	}
>  	kern_type = btf__type_by_id(btf, kern_type_id);
>  
> @@ -979,7 +985,8 @@ find_struct_ops_kern_types(struct bpf_object *obj, const char *tname,
>  	if (kern_vtype_id < 0) {
>  		pr_warn("struct_ops init_kern: struct %s%s is not found in kernel BTF\n",
>  			STRUCT_OPS_VALUE_PREFIX, tname);
> -		return kern_vtype_id;
> +		err = kern_vtype_id;
> +		goto err_out;
>  	}
>  	kern_vtype = btf__type_by_id(btf, kern_vtype_id);
>  
> @@ -997,7 +1004,8 @@ find_struct_ops_kern_types(struct bpf_object *obj, const char *tname,
>  	if (i == btf_vlen(kern_vtype)) {
>  		pr_warn("struct_ops init_kern: struct %s data is not found in struct %s%s\n",
>  			tname, STRUCT_OPS_VALUE_PREFIX, tname);
> -		return -EINVAL;
> +		err = -EINVAL;
> +		goto err_out;
>  	}
>  
>  	*type = kern_type;
> @@ -1007,6 +1015,10 @@ find_struct_ops_kern_types(struct bpf_object *obj, const char *tname,
>  	*data_member = kern_data_member;
>  
>  	return 0;
> +
> +err_out:
> +	free(tname);
> +	return err;
>  }
>  
>  static bool bpf_map__is_struct_ops(const struct bpf_map *map)
> -- 
> 2.43.0
> 

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