[PATCH v2 sched_ext/for-7.1] tools/sched_ext: Add compat handling for sub-scheduler ops

[Andrea Righi <arighi@nvidia.com>]

Extend SCX_OPS_OPEN() with compatibility handling for ops.sub_attach()
and ops.sub_detach(), allowing scx C schedulers with sub-scheduler
support to run on kernels both with and without its support.

Cc: Cheng-Yang Chou <yphbchou0911@gmail.com>
Fixes: ebeca1f930ea ("sched_ext: Introduce cgroup sub-sched support")
Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
Changes in v2:
 - Handle sub_cgroup_id in older kernels (Cheng-Yang Chou)
 - Link to v1: https://lore.kernel.org/all/20260321102036.58734-1-arighi@nvidia.com

 tools/sched_ext/include/scx/compat.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/tools/sched_ext/include/scx/compat.h b/tools/sched_ext/include/scx/compat.h
index 9e0c8f3161e87..039854c490d5e 100644
--- a/tools/sched_ext/include/scx/compat.h
+++ b/tools/sched_ext/include/scx/compat.h
@@ -160,6 +160,7 @@ static inline long scx_hotplug_seq(void)
  * COMPAT:
  * - v6.17: ops.cgroup_set_bandwidth()
  * - v6.19: ops.cgroup_set_idle()
+ * - v7.1:  ops.sub_attach(), ops.sub_detach(), ops.sub_cgroup_id
  */
 #define SCX_OPS_OPEN(__ops_name, __scx_name) ({					\
 	struct __scx_name *__skel;						\
@@ -181,6 +182,21 @@ static inline long scx_hotplug_seq(void)
 		fprintf(stderr, "WARNING: kernel doesn't support ops.cgroup_set_idle()\n"); \
 		__skel->struct_ops.__ops_name->cgroup_set_idle = NULL;	\
 	}									\
+	if (__skel->struct_ops.__ops_name->sub_attach &&			\
+	    !__COMPAT_struct_has_field("sched_ext_ops", "sub_attach")) {	\
+		fprintf(stderr, "WARNING: kernel doesn't support ops.sub_attach()\n"); \
+		__skel->struct_ops.__ops_name->sub_attach = NULL;		\
+	}									\
+	if (__skel->struct_ops.__ops_name->sub_detach &&			\
+	    !__COMPAT_struct_has_field("sched_ext_ops", "sub_detach")) {	\
+		fprintf(stderr, "WARNING: kernel doesn't support ops.sub_detach()\n"); \
+		__skel->struct_ops.__ops_name->sub_detach = NULL;		\
+	}									\
+	if (__skel->struct_ops.__ops_name->sub_cgroup_id > 0 &&		\
+	    !__COMPAT_struct_has_field("sched_ext_ops", "sub_cgroup_id")) { \
+		fprintf(stderr, "WARNING: kernel doesn't support ops.sub_cgroup_id\n"); \
+		__skel->struct_ops.__ops_name->sub_cgroup_id = 0;		\
+	}									\
 	__skel; 								\
 })
 
-- 
2.53.0