void set_tss_gate(int nr, long base, int dpl, long limit) {
char *addr = ((char*)gdt) + _TSS(nr);
*(short*)addr = limit;
*(short*)(addr + 2) = base & 0xffff;
*(addr + 4) = (base >> 16) & 0xff;
*(addr + 5) = 0x80 + ((dpl & 0x03) << 5) + 0x09;
*(addr + 6) = 0x00;
*(addr + 7) = (base >> 24) & 0xff;
}
void init_schedule() {
current = (struct task_t *)0;
tasks_count = 0;
register_task(0);
tasks[0].t_counter = 0;
tasks[0].t_priority = 0;
current = &tasks[0];
asm volatile ("pushfl; andl $0xffffbfff, (%esp); popfl"); /* clear NT */
asm volatile ("ltr %%ax"::"a"(_TSS(0)));
asm volatile ("lldt %%ax"::"a"(_LDT(0)));
}
static void switch_to(int next) {
struct {long a,b;} tmp;
if (&tasks[next] == current) {
return ;
}
if (current) {
current->t_state = TASK_READY;
}
current = &tasks[next];
current->t_state = TASK_RUNNING;
tmp.b = _TSS(next);
asm volatile (
"ljmp %0"
::"m"(*&tmp.a)
);
}
}
void sched_init(void)
{
/* 初始化进程控制块指针数组 */
/* nothing.在bss段,已被清零 */
proc[0] = &init_proc.proc;
current = proc[0];
ticks = 0;
/* 设置进程0的ldt和tss描述符 */
set_ldt_desc(0, V_KERNEL_ZONE_START+(unsigned long)&(proc[0]->ldt));
set_tss_desc(0, V_KERNEL_ZONE_START+(unsigned long)&(proc[0]->tss));
/* 装载进程0的ldt和tss选择符，第一次需我们来加载 */
lldt(_LDT(0));
ltr(_TSS(0));
/* 挂载时钟中断处理程序 */
set_idt(INT_R0, timer_int, NR_TIMER_INT);
/* 设置8253定时器芯片 */
out_b(0x43, 0x36);
out_b(0x40, (LATCH & 0xff));
out_b(0x40, ((LATCH>>8) & 0xff));
/* 挂载系统调用处理程序 */
asmlinkage int sys_fork(struct pt_regs regs) {
struct task_struct *tsk;
int nr;
long flags;
unsigned long used_memory = 0;
save_flags(flags); cli();
// find a free entry in the process table
nr = find_empty_process();
if (nr < 0) {
printk("fork: pids not available at the moment!\n");
goto fork_no_entry;
}
// allocate a page for the process descriptor
tsk = (struct task_struct *) get_free_page();
if (!tsk) {
goto fork_no_mem;
}
// copy descriptor: pid and counter will contain different values for
// father and child
*tsk = *current;
tsk->pid = nr;
tsk->counter = tsk->priority;
// if we are forking the idle process, we assume its child will call an
// exec just after the fork. In this case we do not duplicate code/data.
// If we are forking whatever process, so it is necessary allocate a
// page for it (containing code and data) e setup its LDT to the new
// address space
if (current->pid != 0) {
// allocate memory for code/data
tsk->mem = (char *) get_free_pages(current->used_pages);
if (!tsk->mem) {
goto fork_data_no_mem;
}
// total memory used by current process
used_memory = current->used_pages * PAGE_SIZE;
// copy process data
memcpy(tsk->mem, current->mem, used_memory);
// set up LDT
set_code_desc(&(tsk->ldt[1]), (u_long) tsk->mem, used_memory);
set_data_desc(&(tsk->ldt[2]), (u_long) tsk->mem, used_memory);
}
// setup TSS
tsk->tss.back_link = 0;
tsk->tss.esp0 = PAGE_SIZE + (unsigned long) tsk;
tsk->tss.ss0 = KERNEL_DS;
tsk->tss.esp1 = 0;
tsk->tss.ss1 = 0;
tsk->tss.esp2 = 0;
tsk->tss.ss2 = 0;
tsk->tss.cr3 = 0;
tsk->tss.eip = regs.eip;
tsk->tss.eflags = regs.eflags;
tsk->tss.eax = 0;
tsk->tss.ecx = regs.ecx;
tsk->tss.edx = regs.edx;
tsk->tss.ebx = regs.ebx;
tsk->tss.esp = regs.esp;
tsk->tss.ebp = regs.ebp;
tsk->tss.esi = regs.esi;
tsk->tss.edi = regs.edi;
tsk->tss.es = regs.xes & 0xffff;
tsk->tss.cs = regs.xcs & 0xffff;
tsk->tss.ss = regs.xss & 0xffff;
tsk->tss.ds = regs.xds & 0xffff;
// it is not necessary set FS and GS
tsk->tss.ldt = _LDT(nr);
tsk->tss.trace = 0;
tsk->tss.bitmap = 0xDFFF;
tsk->tss.tr = _TSS(nr);
set_tss_desc(gdt+(nr<<1)+FIRST_TSS_ENTRY, &(tsk->tss));
set_ldt_desc(gdt+(nr<<1)+FIRST_LDT_ENTRY, &(tsk->ldt), 3);
task[nr] = tsk;
restore_flags(flags);
return nr;
fork_data_no_mem:
free_page(tsk);
fork_no_mem:
restore_flags(flags);
return -ENOMEM;
fork_no_entry:
restore_flags(flags);
return -EAGAIN;
}