Re: [PATCH bpf-next v3 02/11] bpf: Drop the recursion depth argument of btf_type_is_scalar_struct()

[Yonghong Song <yonghong.song@linux.dev>]

On 8/27/26 12:04 AM, bot+bpf-ci@kernel.org wrote:
>> commit 05b126fd8e09fdf16e522924b7a453dc9050c44b
>> Author: Yonghong Song <yonghong.song@linux.dev>
>> Date:   Wed Aug 26 23:11:25 2026 -0700
>>
>>      bpf: Drop the recursion depth argument of btf_type_is_scalar_struct()
>>
>>      btf_type_is_scalar_struct() recurses into nested struct members and
>>      carries the nesting depth in a @rec argument, so every caller has to
>>      spell out the 0 that starts the walk.
>>
>>      Move the recursion into a static helper that keeps @rec and leave
>>      btf_type_is_scalar_struct() as a thin wrapper over it, so callers only
>>      name the type they are asking about.
>>
>>      No functional change.
> This isn't a bug, but would it help to say the split is in preparation
> for giving the walk extra state, rather than presenting it as call-site
> tidying?
>
> Looking at the next patch in the series, 'bpf: Let the by-value struct
> walk take the kinds of member it accepts', a @member_kinds parameter is
> added to exactly this walk helper, which looks like the load-bearing
> reason for introducing the wrapper now. As written, a reviewer reading
> this patch alone sees only a cosmetic change and has no way to tell it
> is groundwork.

I think we are fine. This is a pure refactoring to remove a parameter
for a global function.

>
>> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
>> index 004b06785521c..3eb61edc8c5e1 100644
>> --- a/include/linux/bpf_verifier.h
>> +++ b/include/linux/bpf_verifier.h
>> @@ -1489,7 +1489,7 @@ struct bpf_iarray *bpf_insn_successors(struct bpf_verifier_env *env, u32 idx);
>>   void bpf_fmt_stack_mask(char *buf, ssize_t buf_sz, u64 stack_mask);
>>   bool bpf_subprog_is_global(const struct bpf_verifier_env *env, int subprog);
>>   bool btf_type_is_scalar_struct(struct bpf_verifier_env *env, const struct btf *btf,
>> -			       const struct btf_type *t, int rec);
>> +			       const struct btf_type *t);
>>
>>   int bpf_find_subprog(struct bpf_verifier_env *env, int off);
>>   bool bpf_is_throw_kfunc(struct bpf_insn *insn);
> [ ... ]
>
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 5d8162e13c208..bc3053e81500f 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -11647,9 +11647,8 @@ static bool is_kfunc_arg_implicit(const struct bpf_call_arg_meta *meta, u32 arg_
>>   }
>>
>>   /* Returns true if struct is composed of scalars, 4 levels of nesting allowed */
>> -bool btf_type_is_scalar_struct(struct bpf_verifier_env *env,
>> -			       const struct btf *btf,
>> -			       const struct btf_type *t, int rec)
>> +static bool btf_scalar_struct_walk(struct bpf_verifier_env *env, const struct btf *btf,
>> +				   const struct btf_type *t, int rec)
>>   {
>>   	const struct btf_type *member_type;
>>   	const struct btf_member *member;
>> @@ -11667,7 +11666,7 @@ bool btf_type_is_scalar_struct(struct bpf_verifier_env *env,
>>   				verbose(env, "max struct nesting depth exceeded\n");
>>   				return false;
>>   			}
>> -			if (!btf_type_is_scalar_struct(env, btf, member_type, rec + 1))
>> +			if (!btf_scalar_struct_walk(env, btf, member_type, rec + 1))
>>   				return false;
>>   			continue;
>>   		}
>> @@ -11686,6 +11685,13 @@ bool btf_type_is_scalar_struct(struct bpf_verifier_env *env,
>>   	return true;
>>   }
>>
>> +bool btf_type_is_scalar_struct(struct bpf_verifier_env *env,
>> +			       const struct btf *btf,
>> +			       const struct btf_type *t)
>> +{
>> +	return btf_scalar_struct_walk(env, btf, t, 0);
>> +}
> This isn't a bug, but since the following patch renames both of these,
> could this patch introduce the final names directly so the call sites
> and the header prototype are only touched once?
>
> Both names introduced here are renamed one commit later in the same
> series: btf_scalar_struct_walk() becomes btf_struct_member_walk() and
> btf_type_is_scalar_struct() becomes btf_struct_is_composed_of() in
> 'bpf: Let the by-value struct walk take the kinds of member it accepts',
> which also re-touches the include/linux/bpf_verifier.h prototype and
> all six call sites a second time.

Not sure what is going here. The following is actual code:

+bool btf_type_is_scalar_struct(struct bpf_verifier_env *env,
+                              const struct btf *btf,
+                              const struct btf_type *t)
+{
+       return btf_struct_member_walk(env, btf, t, 0);
+}

which does not have btf_scalar_struct_walk().

>
> [ ... ]
>
>
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
>
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/33045482525