/* *  linux/kernel/fork.c * *  (C) 1991  Linus Torvalds *//* *  'fork.c' contains the help-routines for the 'fork' system call * (see also system_call.s), and some misc functions ('verify_area'). * Fork is rather simple, once you get the hang of it, but the memory * management can be a bitch. See 'mm/mm.c': 'copy_page_tables()' */#include <errno.h>#include <linux/sched.h>#include <linux/kernel.h>#include <asm/segment.h>#include <asm/system.h>extern void write_verify(unsigned long address);extern int fprintk(int fd, const char *fmt, ...);long last_pid=0;void verify_area(void * addr,int size){	unsigned long start;	start = (unsigned long) addr;	size += start & 0xfff;	start &= 0xfffff000;	start += get_base(current->ldt[2]);	while (size>0) {		size -= 4096;		write_verify(start);		start += 4096;	}}int copy_mem(int nr,struct task_struct * p){	unsigned long old_data_base,new_data_base,data_limit;	unsigned long old_code_base,new_code_base,code_limit;	code_limit=get_limit(0x0f);	data_limit=get_limit(0x17);	old_code_base = get_base(current->ldt[1]);	old_data_base = get_base(current->ldt[2]);	if (old_data_base != old_code_base)		panic("We don't support separate I&D");	if (data_limit < code_limit)		panic("Bad data_limit");	new_data_base = new_code_base = nr * 0x4000000;	p->start_code = new_code_base;	set_base(p->ldt[1],new_code_base);	set_base(p->ldt[2],new_data_base);	if (copy_page_tables(old_data_base,new_data_base,data_limit)) {		printk("free_page_tables: from copy_mem\n");		free_page_tables(new_data_base,data_limit);		return -ENOMEM;	}	return 0;}/* *  Ok, this is the main fork-routine. It copies the system process * information (task[nr]) and sets up the necessary registers. It * also copies the data segment in it's entirety. */int copy_process(int nr,long ebp,long edi,long esi,long gs,long none,		long ebx,long ecx,long edx,		long fs,long es,long ds,		long eip,long cs,long eflags,long esp,long ss){	struct task_struct *p;	int i;	struct file *f;	p = (struct task_struct *) get_free_page();	if (!p)		return -EAGAIN;		task[nr] = p;	*p = *current;	/* NOTE! this doesn't copy the supervisor stack */		p->state = TASK_UNINTERRUPTIBLE;	p->pid = last_pid;		p->father = current->pid;	p->counter = p->priority;	p->signal = 0;	p->alarm = 0;	p->leader = 0;		/* process leadership doesn't inherit */	p->utime = p->stime = 0;	p->cutime = p->cstime = 0;	p->start_time = jiffies;	p->tss.back_link = 0;	p->tss.esp0 = PAGE_SIZE + (long) p;	p->tss.ss0 = 0x10;	p->tss.eip = eip;	p->tss.eflags = eflags;	p->tss.eax = 0;	p->tss.ecx = ecx;	p->tss.edx = edx;	p->tss.ebx = ebx;	p->tss.esp = esp;	p->tss.ebp = ebp;	p->tss.esi = esi;	p->tss.edi = edi;	p->tss.es = es & 0xffff;	p->tss.cs = cs & 0xffff;	p->tss.ss = ss & 0xffff;	p->tss.ds = ds & 0xffff;	p->tss.fs = fs & 0xffff;	p->tss.gs = gs & 0xffff;	p->tss.ldt = _LDT(nr);	p->tss.trace_bitmap = 0x80000000;	if (last_task_used_math == current)		__asm__("clts ; fnsave %0"::"m" (p->tss.i387));	if (copy_mem(nr,p)) {		task[nr] = NULL;		free_page((long) p);		return -EAGAIN;	}	for (i=0; i<NR_OPEN;i++)		if ((f=p->filp[i]))			f->f_count++;	if (current->pwd)		current->pwd->i_count++;	if (current->root)		current->root->i_count++;	if (current->executable)		current->executable->i_count++;	set_tss_desc(gdt+(nr<<1)+FIRST_TSS_ENTRY,&(p->tss));	set_ldt_desc(gdt+(nr<<1)+FIRST_LDT_ENTRY,&(p->ldt));	fprintk(3, "%ld\t%c\t%ld\n", p->pid, 'N', jiffies); //向log文件輸出			p->state = TASK_RUNNING;	/* do this last, just in case */	fprintk(3, "%ld\t%c\t%ld\n", p->pid, 'J', jiffies); //向log文件輸出	return last_pid;}int find_empty_process(void){	int i;	repeat:		if ((++last_pid)<0) last_pid=1;		for(i=0 ; i<NR_TASKS ; i++)			if (task[i] && task[i]->pid == last_pid) goto repeat;	for(i=1 ; i<NR_TASKS ; i++)		if (!task[i])			return i;	return -EAGAIN;}