Re: [PATCH v2] tools/sched_ext: use btf_vlen() helper in compat.h

[Andrea Righi]

On Tue, Jun 30, 2026 at 04:17:20PM +0800, luoliang@xxxxxxxxxx wrote:
> From: luoliang <luoliang@xxxxxxxxxx>
> 
> __COMPAT_read_enum() and __COMPAT_struct_has_field() open-code the
> vlen lookup via the raw BTF_INFO_VLEN(t->info) UAPI macro. libbpf
> exposes btf_vlen() for exactly this purpose; use it in the three
> call sites, matching the pattern in kernel/bpf/inode.c and
> tools/bpf/bpftool.
> 
> btf_vlen() returns __u32 (since commit cacd6729c0923, "libbpf:
> Adjust btf_vlen() to return a __u32", which expanded the BTF vlen
> field from 16 to 24 bits). Declare the loop counters as __u32 to
> match the return type, keeping the comparison as a plain
> '__u32 < __u32' and silencing the -Wsign-compare warnings.
> 
> No functional change.
> 
> Suggested-by: Andrea Righi <arighi@xxxxxxxxxx>
> Signed-off-by: Liang Luo <luoliang@xxxxxxxxxx>

Looks good.

Reviewed-by: Andrea Righi <arighi@xxxxxxxxxx>

Thanks!
-Andrea

> 
> ---
> 
> Changes in v2:
> - Correct the commit message: btf_vlen() returns __u32 (not __u16)
>   on mainline since cacd6729c0923. The v1 description was accurate
>   only on a v7.1 baseline. (Thanks to Sashiko AI review and Andrea
>   Righi for catching this.)
> - Declare the loop counters as __u32 to match btf_vlen()'s return
>   type, as suggested by Andrea Righi. This properly silences
>   -Wsign-compare on mainline.
> ---
>  tools/sched_ext/include/scx/compat.h | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/sched_ext/include/scx/compat.h b/tools/sched_ext/include/scx/compat.h
> index 602f07061ee3..23d9ef3e4c9d 100644
> --- a/tools/sched_ext/include/scx/compat.h
> +++ b/tools/sched_ext/include/scx/compat.h
> @@ -28,7 +28,7 @@ static inline bool __COMPAT_read_enum(const char *type, const char *name, u64 *v
>  	const struct btf_type *t;
>  	const char *n;
>  	s32 tid;
> -	int i;
> +	__u32 i;
>  
>  	__COMPAT_load_vmlinux_btf();
>  
> @@ -42,7 +42,7 @@ static inline bool __COMPAT_read_enum(const char *type, const char *name, u64 *v
>  	if (btf_is_enum(t)) {
>  		struct btf_enum *e = btf_enum(t);
>  
> -		for (i = 0; i < BTF_INFO_VLEN(t->info); i++) {
> +		for (i = 0; i < btf_vlen(t); i++) {
>  			n = btf__name_by_offset(__COMPAT_vmlinux_btf, e[i].name_off);
>  			SCX_BUG_ON(!n, "btf__name_by_offset()");
>  			if (!strcmp(n, name)) {
> @@ -53,7 +53,7 @@ static inline bool __COMPAT_read_enum(const char *type, const char *name, u64 *v
>  	} else if (btf_is_enum64(t)) {
>  		struct btf_enum64 *e = btf_enum64(t);
>  
> -		for (i = 0; i < BTF_INFO_VLEN(t->info); i++) {
> +		for (i = 0; i < btf_vlen(t); i++) {
>  			n = btf__name_by_offset(__COMPAT_vmlinux_btf, e[i].name_off);
>  			SCX_BUG_ON(!n, "btf__name_by_offset()");
>  			if (!strcmp(n, name)) {
> @@ -85,7 +85,7 @@ static inline bool __COMPAT_struct_has_field(const char *type, const char *field
>  	const struct btf_member *m;
>  	const char *n;
>  	s32 tid;
> -	int i;
> +	__u32 i;
>  
>  	__COMPAT_load_vmlinux_btf();
>  	tid = btf__find_by_name_kind(__COMPAT_vmlinux_btf, type, BTF_KIND_STRUCT);
> @@ -97,7 +97,7 @@ static inline bool __COMPAT_struct_has_field(const char *type, const char *field
>  
>  	m = btf_members(t);
>  
> -	for (i = 0; i < BTF_INFO_VLEN(t->info); i++) {
> +	for (i = 0; i < btf_vlen(t); i++) {
>  		n = btf__name_by_offset(__COMPAT_vmlinux_btf, m[i].name_off);
>  		SCX_BUG_ON(!n, "btf__name_by_offset()");
>  			if (!strcmp(n, field))
> -- 
> 2.43.0
>