linux_lab_os_exp2/fork.c

/*
 *  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);

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,int flag)
{
	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,flag)) {
		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 flag,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;
	__asm__ volatile ("cld");   /* by wyj */
	*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,flag)) {
		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));
	p->state = TASK_RUNNING;	/* do this last, just in case */
	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;
}

/*
	直接让esp（子进程）指向另一个进程（当前进程）的地址；
	修改eip对应的指令，改为ret 0xec8353c3  ps:应该只有0xc3有用
	由于eip只执行一条指令，我们将eip指向栈，将ret压入栈即可；
	在这里我们只实现了int (*fn)(void *) 一种函数类型，并且要求fn内以exit结尾
	于是我们只需修改八字节即可；
	下面写的不对，不能指向另一个进程的地址，只能修改物理页了。
*/
int do_clone(int nr,long tmp,int (*fn)(void *), void *child_stack, int flag) 
{
	//设置压栈表，方便操作；
	long stack[1024];
	unsigned long len=0;
	task[nr]->tss.esp=(unsigned long) child_stack - 8;
	stack[0] = (unsigned long) fn;
	task[nr]->tss.eip = (unsigned long) child_stack - 4;
	stack[1]= 0xec8353c3;
	//栈区赋值；
	len = 8;
	char *p1=stack ,*p2=(char *)((unsigned long)child_stack-len);
	while(len--)
		put_fs_byte(*(p1++),p2++);
	return 0;
}
/*
	共享物理页：写法有缺陷，可能child——stack跨页
	//子进程task[nr]的页表项获取，目的是更新成child——stacK的物理页
	nrfrom_page =  ((address>>20) & 0xffc);
	nrfrom_page += ((task[nr]->start_code>>20) & 0xffc);//页目录
	nrfrom=*(unsigned long *)nrfrom_page;	//页表项
	if(!(nrfrom&1)) //无页表项分配一个
	{
		if(!(tpage=get_free_page()))
		{
			printk("out of memory.\n");
			return -1;
		}
		else
			{
				*(unsigned long *)nrfrom_page= tpage | 7;
				mem_map[(tpage-LOW_MEM)>>12]++;
			}
	}
	nrfrom &= 0xfffff000;
	nrfrom_page = nrfrom + ((address>>10) & 0xffc);

	//获取child_stack的物理页,并将其复制给task[nr];
	address=(unsigned long) child_stack;
	from_page =  ((address>>20) & 0xffc);
	from_page += ((current->start_code>>20) & 0xffc);//页目录
	if(!(*(unsigned long *)from_page&1))  //页表项不存在，申请页面
		if(!(tpage=get_free_page()))
		{
			printk("out of memory.\n");
			return -1;
		}
		else
			{
				*(unsigned long *)from_page= tpage | 7;
				mem_map[(tpage-LOW_MEM)>>12]++;
			}
	from=*(unsigned long *)from_page;	//页表项
	from &= 0xfffff000;
	from_page = from + ((address>>10) & 0xffc);
	if(!(*(unsigned long *)from_page & 1))	//物理页不存在
		if(!(tpage=get_free_page()))
		{
			printk("out of memory.\n");
			return -1;
		}
		else
		{
			*(unsigned long *)from_page= tpage | 7; 
			mem_map[(tpage-LOW_MEM)>>12]++;
		}
	//复制给nr
	*(unsigned long *)nrfrom_page = *(unsigned long *)from_page;

	//更新esp,让其指向child_stack同样偏移的地点;
	task[nr]->tss.esp=(unsigned long) child_stack;

	//注意：这里child_stack 指向的是高地址，要向下面push.
	unsigned long phy_addr = (*(unsigned long *)nrfrom_page & 0xfffff000) | ((unsigned long) child_stack & 0xfff);
	if(argv)//参数列表不为空，将参数压入栈中，这里直接修改物理页
	{

	}
	//char * tmp1=nrfrom, *tmp2=child_stack-1024,len=;
	//while()
	return 0;
}
*/