sched: Manipulate sched classes via sched hooks

This skill also apply to shell to manipulate varity of cmds. The major
difference is identification. Because sched hooks are out of order,
I create a new member in `struct sched` to identify the sched class.

include/kernel/sched.h

@@ -11,21 +11,29 @@ struct thread_info;
 
 #define SCHED_CLASS_RR 0
 #define SCHED_CLASS_BITMAP 1
+typedef int sched_class_t;
 
 #define SCHED_OPT_NONE 0
 #define SCHED_OPT_RESTORE_ONLY 1
 #define SCHED_OPT_RESET 2
 #define SCHED_OPT_TICK 3
 
+/* scheduler implementation hooks */
+#define HOOK_SCHED_CLASS(name, sched_struct)                            \
+    static struct sched *sched_class_##name                             \
+        __attribute__((section(".sched.class"), aligned(sizeof(long)),  \
+                        used)) = sched_struct;
+
 struct sched {
+    sched_class_t class_type;
     int (*init)(void);
     int (*enqueue)(struct thread_info *thread);
     int (*dequeue)(struct thread_info *thread);
     int (*elect)(int switch_type);
 };
 
 int sched_init();
-int sched_select(int sched_type);
+int sched_select(sched_class_t sched_type);
 int sched_enqueue(struct thread_info *thread);
 int sched_dequeue(struct thread_info *thread);
 int sched_elect(int flags);

kernel/sched.c

@@ -1,35 +1,48 @@
 #include <kernel/sched.h>
 #include <kernel/thread.h>
 
-extern const struct sched sched_rr;
-extern const struct sched sched_bitmap;
+extern unsigned long __sched_classes_start__;
+extern unsigned long __sched_classes_end__;
 
-static const struct sched *sched;
+/* static vars to repesent sched classes list */
+static struct sched **sched_classes = 
+    (struct sched **) &__sched_classes_start__;
+static struct sched **sched_classes_end = 
+    (struct sched **) &__sched_classes_end__;
+
+static struct sched *sched;
 
 int sched_init()
 {
-    int ret;
+    int ret = 0;
 
-    ret = sched_rr.init();
-    ret = sched_bitmap.init();
+    /* Initialize each scheduler class by traversing hooks */
+    for (struct sched **c = sched_classes;
+            c < sched_classes_end; c++) {
+        struct sched *class = *c;
+        ret |= class->init();
+    }
 
     return ret;
 }
 
-int sched_select(int sched_type)
+int sched_select(sched_class_t sched_type)
 {
-    switch (sched_type) {
-    case SCHED_CLASS_RR:
-        sched = &sched_rr;
-        break;
-    case SCHED_CLASS_BITMAP:
-        sched = &sched_bitmap;
-        break;
-    default:
-        return -1;
+    int ret = -1;
+    struct sched *class = NULL;
+
+    /* Examine specified sched class in hooks or not */
+    for (struct sched **c = sched_classes;
+            c < sched_classes_end; c++)
+        if (sched_type == (*c)->class_type)
+            class = *c;
+
+    if (class) {
+        sched = class;
+        ret = 0;
     }
 
-    return 0;
+    return ret;
 }
 
 int sched_enqueue(struct thread_info *thread)

kernel/sched/bitmap.c

@@ -112,10 +112,13 @@ static int sched_bitmap_elect(int flags)
 }
 
 // clang-format off
-const struct sched sched_bitmap = {
+static struct sched sched_bitmap = {
+    .class_type = SCHED_CLASS_BITMAP,
     .init = sched_bitmap_init,
     .enqueue = sched_bitmap_enqueue,
     .dequeue = sched_bitmap_dequeue,
     .elect = sched_bitmap_elect,
 };
 // clang-format on
+
+HOOK_SCHED_CLASS(bitmap, &sched_bitmap)

kernel/sched/rr.c

@@ -87,10 +87,13 @@ int sched_rr_elect(int switch_type)
 }
 
 // clang-format off
-const struct sched sched_rr = {
+static struct sched sched_rr = {
+    .class_type = SCHED_CLASS_RR,
     .init = sched_rr_init,
     .enqueue = sched_rr_enqueue,
     .dequeue = sched_rr_dequeue,
     .elect = sched_rr_elect,
 };
 // clang-format on
+
+HOOK_SCHED_CLASS(RR, &sched_rr)

piko.lds.S

@@ -24,6 +24,9 @@ SECTIONS
         PROVIDE(__shell_cmd_start__ = .);
         KEEP(*(.shell_cmd*))
         PROVIDE(__shell_cmd_end__ = .);
+        PROVIDE(__sched_classes_start__ = .);
+        KEEP(*(.sched.class*))
+        PROVIDE(__sched_classes_end__ = .);
         PROVIDE(__rodata_start__ = .);
         *(.rodata*)
         PROVIDE(__rodata_end__ = .);