scx: Use the new struct_ops compatibililty mechanism

tools/sched_ext/include/scx/compat.bpf.h

@@ -35,54 +35,13 @@ static inline void __COMPAT_scx_bpf_switch_all(void)
 }
 
 /*
- * sched_ext_ops.exit_dump_len is a recent addition. Use the following
- * definition to support older kernels. See scx_qmap for usage example.
+ * Define sched_ext_ops. This may be expanded to define multiple variants for
+ * backward compatibility. See compat.h::SCX_OPS_LOAD/ATTACH().
  */
-struct sched_ext_ops___no_exit_dump_len {
-	s32 (*select_cpu)(struct task_struct *, s32, u64);
-	void (*enqueue)(struct task_struct *, u64);
-	void (*dequeue)(struct task_struct *, u64);
-	void (*dispatch)(s32, struct task_struct *);
-	void (*runnable)(struct task_struct *, u64);
-	void (*running)(struct task_struct *);
-	void (*stopping)(struct task_struct *, bool);
-	void (*quiescent)(struct task_struct *, u64);
-	bool (*yield)(struct task_struct *, struct task_struct *);
-	bool (*core_sched_before)(struct task_struct *, struct task_struct *);
-	void (*set_weight)(struct task_struct *, u32);
-	void (*set_cpumask)(struct task_struct *, const struct cpumask *);
-	void (*update_idle)(s32, bool);
-	void (*cpu_acquire)(s32, struct scx_cpu_acquire_args *);
-	void (*cpu_release)(s32, struct scx_cpu_release_args *);
-	s32 (*init_task)(struct task_struct *, struct scx_init_task_args *);
-	void (*exit_task)(struct task_struct *, struct scx_exit_task_args *);
-	void (*enable)(struct task_struct *);
-	void (*disable)(struct task_struct *);
-	s32 (*cgroup_init)(struct cgroup *, struct scx_cgroup_init_args *);
-	void (*cgroup_exit)(struct cgroup *);
-	s32 (*cgroup_prep_move)(struct task_struct *, struct cgroup *, struct cgroup *);
-	void (*cgroup_move)(struct task_struct *, struct cgroup *, struct cgroup *);
-	void (*cgroup_cancel_move)(struct task_struct *, struct cgroup *, struct cgroup *);
-	void (*cgroup_set_weight)(struct cgroup *, u32);
-	void (*cpu_online)(s32);
-	void (*cpu_offline)(s32);
-	s32 (*init)();
-	void (*exit)(struct scx_exit_info *);
-	u32 dispatch_max_batch;
-	u64 flags;
-	u32 timeout_ms;
-	char name[128];
-};
-
-/* define sched_ext_ops, see compat.h::SCX_OPS_LOAD/ATTACH() */
 #define SCX_OPS_DEFINE(__name, ...)						\
 	SEC(".struct_ops.link")							\
 	struct sched_ext_ops __name = {						\
 		__VA_ARGS__,							\
-	};									\
-	SEC(".struct_ops.link")							\
-	struct sched_ext_ops___no_exit_dump_len __name##___no_exit_dump_len = {	\
-		__VA_ARGS__							\
-	};									\
+	};
 
 #endif	/* __SCX_COMPAT_BPF_H */

tools/sched_ext/include/scx/compat.h

@@ -118,24 +118,17 @@ static inline bool __COMPAT_struct_has_field(const char *type, const char *field
  */
 #define SCX_OPS_LOAD(__skel, __ops_name, __scx_name, __uei_name) ({		\
 	UEI_SET_SIZE(__skel, __ops_name, __uei_name);				\
-	if (__COMPAT_struct_has_field("sched_ext_ops", "exit_dump_len")) {	\
-		bpf_map__set_autocreate((__skel)->maps.__ops_name, true);	\
-		bpf_map__set_autocreate((__skel)->maps.__ops_name##___no_exit_dump_len, false); \
-	} else {								\
-		if ((__skel)->struct_ops.__ops_name->exit_dump_len)		\
-			fprintf(stderr, "WARNING: kernel doesn't support setting exit dump len\n"); \
-		bpf_map__set_autocreate((__skel)->maps.__ops_name, false);	\
-		bpf_map__set_autocreate((__skel)->maps.__ops_name##___no_exit_dump_len, true); \
+	if (__COMPAT_struct_has_field("sched_ext_ops", "exit_dump_len") &&	\
+	    (__skel)->struct_ops.__ops_name->exit_dump_len) {			\
+		fprintf(stderr, "WARNING: kernel doesn't support setting exit dump len\n"); \
+		(__skel)->struct_ops.__ops_name->exit_dump_len = 0;	\
 	}									\
 	SCX_BUG_ON(__scx_name##__load((__skel)), "Failed to load skel");	\
 })
 
 #define SCX_OPS_ATTACH(__skel, __ops_name) ({					\
 	struct bpf_link *__link;						\
-	if (__COMPAT_struct_has_field("sched_ext_ops", "exit_dump_len"))	\
-		__link = bpf_map__attach_struct_ops((__skel)->maps.__ops_name);	\
-	else									\
-		__link = bpf_map__attach_struct_ops((__skel)->maps.__ops_name##___no_exit_dump_len); \
+	__link = bpf_map__attach_struct_ops((__skel)->maps.__ops_name);		\
 	SCX_BUG_ON(!__link, "Failed to attach struct_ops");			\
 	__link;									\
 })