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

[luoliang]

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>

---

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