From be74842e37ad54f4fd18ae647e2bdf3e435a0fb8 Mon Sep 17 00:00:00 2001
From: Jake Mannens <jake72360@gmail.com>
Date: Fri, 13 Jul 2018 03:51:23 +1000
Subject: Added a state field to the task structure to hold the task's run
 state. Now, reschedule() requires a task to be in the TSTATE_RUNNING state
 for it to run.

Renamed the TSS structure within the task structure from 'state' to
'tss' to avoid confusion with the task's run state.

Removed the task_state structure declaration from sched.c as it is no
longer needed due to context switches now being performed entirely in
hardware.

Removed the cstate pointer from sched.c. Interrupt handlers no longer
set a pointer to saved state information on the stack since this was
only needed for software task switching. NOTE: This may be re-introduced
should it become necessary to access state information on the stack.

Added a basic implementation of the wake_up() scheduling primative. This
function is currently not used and may be completely re-written in
future.
---
 kernel/sched.c | 56 +++++++++++++++++++++++---------------------------------
 1 file changed, 23 insertions(+), 33 deletions(-)

(limited to 'kernel/sched.c')

diff --git a/kernel/sched.c b/kernel/sched.c
index 675867c..efbb80a 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -30,26 +30,8 @@
 extern char _usrbin_start;
 extern char _usrbin_size;
 
-struct task_state {
-  uint16_t ds;
-  uint32_t edi;
-  uint32_t esi;
-  uint32_t ebp;
-  uint32_t esp_garbage;
-  uint32_t ebx;
-  uint32_t edx;
-  uint32_t ecx;
-  uint32_t eax;
-  uint32_t eip;
-  uint32_t cs;
-  uint32_t eflags;
-  uint32_t esp;
-  uint32_t ss;
-} __attribute__((packed));
-
 struct task_struct *ctask;
 uint32_t ctaskn;
-struct task_state *cstate;
 
 static struct task_struct tasks[NRTASKS];
 
@@ -79,7 +61,7 @@ struct task_struct *create_proc(void *bin, size_t len) {
     if(!tasks[i].pid) {
       task = &tasks[i];
       /* update the GDT */
-      set_tss(i, &tasks[i].state);
+      set_tss(i, &tasks[i].tss);
       break;
     }
   }
@@ -169,21 +151,22 @@ struct task_struct *create_proc(void *bin, size_t len) {
    */
   memset(task, 0, sizeof(struct task_struct));
   task->pid = nextpid;
-  task->state.cr3 = (uint32_t) pdir;
-  task->state.cs = 0x1B;
-  task->state.ds = 0x23;
-  task->state.es = 0x23;
-  task->state.fs = 0x23;
-  task->state.gs = 0x23;
-  task->state.ss = 0x23;
-  task->state.eip = (uint32_t) USRSTART;
-  task->state.esp = 0xFFFFDFFF;
-  task->state.esp0 = 0xFFFFFFFF;
-  task->state.ss0 = 0x10;
+  task->state = TSTATE_RUNNING;
+  task->tss.cr3 = (uint32_t) pdir;
+  task->tss.cs = 0x1B;
+  task->tss.ds = 0x23;
+  task->tss.es = 0x23;
+  task->tss.fs = 0x23;
+  task->tss.gs = 0x23;
+  task->tss.ss = 0x23;
+  task->tss.eip = (uint32_t) USRSTART;
+  task->tss.esp = 0xFFFFDFFF;
+  task->tss.esp0 = 0xFFFFFFFF;
+  task->tss.ss0 = 0x10;
   __asm__ (
       "pushf\n" \
       "pop %%eax" \
-      : "=a" (task->state.eflags) \
+      : "=a" (task->tss.eflags) \
       ::);
 
   return task;
@@ -199,7 +182,6 @@ void sched_init(void) {
 
   nextpid = 1;
   ctask = NULL;
-  cstate = NULL;
 
   create_proc(&_usrbin_start, (size_t) &_usrbin_size);
   create_proc(&_usrbin_start, (size_t) &_usrbin_size);
@@ -218,7 +200,7 @@ void reschedule(void) {
   n = ctaskn;
   for(i = 0; i < NRTASKS; i++) {
     n = (n + 1) % NRTASKS;
-    if(tasks[n].pid)
+    if(tasks[n].pid && tasks[n].state == TSTATE_RUNNING)
       break;
   }
   switch_to(n, &tasks[n]);
@@ -227,3 +209,11 @@ void reschedule(void) {
 void sched_tick(void) {
   reschedule();
 }
+
+void wake_up(struct task_struct **task) {
+  if(task == NULL || *task == NULL)
+    return;
+
+  (*task)->state = TSTATE_RUNNING;
+  *task = NULL;
+}
-- 
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