From fb7895bc23ce4359a3574103ae4a7864669e5a95 Mon Sep 17 00:00:00 2001
From: Danny Holman <dholman@gymli.org>
Date: Wed, 29 May 2024 01:23:40 -0500
Subject: kernel: sched: implement the round-robin scheduler

Implement a basic round-robin scheduler and tie it to the PIT timer
interrupt on x86.

Signed-off-by: Danny Holman <dholman@gymli.org>
---
 include/kernel/sched.h |  27 +++++--------
 kernel/sched.c         | 108 +++++++++++++++++++++++++------------------------
 2 files changed, 66 insertions(+), 69 deletions(-)

diff --git a/include/kernel/sched.h b/include/kernel/sched.h
index fef36b8..00a5d95 100644
--- a/include/kernel/sched.h
+++ b/include/kernel/sched.h
@@ -2,26 +2,19 @@
 #define KERNEL_SCHED_H
 
 #include <kernel/asm.h>
-#include <kernel/data/list.h>
-
-#define THREAD_READY    0
-#define THREAD_RUNNING  1
-#define THREAD_WAIT     2
-
-struct task_block {
-        unsigned int pid;
-        unsigned int parent_pid;
-        int nice;
-        unsigned int num_threads;
-        struct thread_block *threads;
-        struct list_head list;
-};
+#include <kernel/kthread.h>
+#include <stdint.h>
 
 void sched_init(void);
 void schedule_next(void);
+void schedule_thread(struct kthread *thread);
+
+void block_thread(struct kthread *thread);
+void unblock_thread(struct kthread *thread);
+
+void sched_lock(void);
+void sched_unlock(void);
 
-struct task_block* init_task(int nice, unsigned int ppid);
-void schedule_thread(struct thread_block *thread);
-void switch_thread(struct thread_block *old, struct thread_block *new);
+void switch_thread(struct kthread *old, struct kthread *new);
 
 #endif
diff --git a/kernel/sched.c b/kernel/sched.c
index d893813..b6096da 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1,70 +1,74 @@
 #include <kernel/sched.h>
-#include <kernel/container_of.h>
-#include <kernel/data/list.h>
-#include <kernel/string.h>
-#include <kernel/kmalloc.h>
+#include <kernel/kthread.h>
+#include <kernel/panic.h>
+#include <libk/io.h>
+#include <libk/kmalloc.h>
+#include <libk/string.h>
 #include <stddef.h>
 
-static struct list_head *ready_queue;
-static struct list_head *wait_queue;
-
-static struct task_block *cur = NULL;
-static long int next_id = 1;
+static struct kthread *run_queue = NULL;
+static struct kthread *wait_queue = NULL;
+static struct kthread *cur = NULL;
 
 static int scheduler_enabled = 0;
-
-static void _enqueue(struct list_head *queue, struct task_block *task) {
-        struct list_head *temp = queue;
-        while (temp->next != NULL)
-                temp = temp->next;
-        list_add(&task->list, temp);
-}
-
-static struct task_block* _dequeue(struct list_head *queue) {
-        if (queue->next == NULL)
-                return NULL;
-        struct list_head *temp = queue->next;
-        list_del(temp);
-        struct task_block *ret = container_of(temp, struct task_block, list);
-        return ret;
-}
+static struct kmutex scheduler_lock;
 
 void sched_init(void) {
-        ready_queue = kmalloc(sizeof(struct list_head));
-        wait_queue = kmalloc(sizeof(struct list_head));
-        struct task_block *boot_task = init_task(0, 0);
-        boot_task->threads->state = THREAD_RUNNING;
-        cur = boot_task;
-
-        switch_thread(boot_task->threads, boot_task->threads);
+        disable_ints();
+        cur = kthread_create(NULL, NULL);
+        cur->stack = NULL;
+        switch_thread(cur, cur);
+        cur->state = THREAD_RUNNING;
         scheduler_enabled = 1;
+        enable_ints();
 }
 
 void schedule_next(void) {
         if (scheduler_enabled == 0)
                 return;
+        if (run_queue == NULL)
+                return;
 
-        struct task_block *task = _dequeue(ready_queue);
-        if (task == NULL)
+        struct kthread *thread = cur;
+        schedule_thread(cur);
+        cur = run_queue;
+        run_queue = run_queue->next;
+        cur->next = NULL;
+        cur->state = THREAD_RUNNING;
+        switch_thread(thread, cur);
+}
+
+void schedule_thread(struct kthread *thread) {
+        if (run_queue == NULL) {
+                run_queue = thread;
                 return;
-        if (cur != NULL)
-                _enqueue(ready_queue, cur);
-        disable_ints();
-        switch_thread(cur->threads, task->threads);
-        enable_ints();
-        task->threads->state = THREAD_RUNNING;
-        cur->threads->state = THREAD_READY;
-        cur = task;
+        }
+
+        kmutex_lock(&scheduler_lock);
+        struct kthread *temp = run_queue;
+        while (temp->next != NULL)
+                temp = temp->next;
+        temp->next = thread;
+        thread->state = THREAD_READY;
+        kmutex_unlock(&scheduler_lock);
 }
 
-struct task_block* init_task(int nice, unsigned int ppid) {
-        struct task_block *ret = kmalloc(sizeof(struct task_block));
-        ret->pid = next_id++;
-        ret->parent_pid = ppid;
-        ret->nice = nice;
-        ret->num_threads = 1;
-        ret->threads = kmalloc(sizeof(struct thread_block));
-        ret->threads->tid = ret->pid;
-        ret->threads->tgid = ret->pid;
-        return ret;
+void block_thread(struct kthread *thread) {
+        kmutex_lock(&scheduler_lock);
+        thread->next = wait_queue;
+        wait_queue = thread;
+        kmutex_unlock(&scheduler_lock);
+}
+
+void unblock_thread(struct kthread *thread) {
+        kmutex_lock(&scheduler_lock);
+        struct kthread *temp = wait_queue;
+        while (temp != NULL) {
+                if (temp->next == thread) {
+                        temp->next = thread->next;
+                        return;
+                }
+                temp = temp->next;
+        }
+        kmutex_unlock(&scheduler_lock);
 }
-- 
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