linux_lab_os_exp2/linux/mm/memory.c

/*
 *  linux/mm/memory.c
 *
 *  (C) 1991  Linus Torvalds
 */

/*
 * demand-loading started 01.12.91 - seems it is high on the list of
 * things wanted, and it should be easy to implement. - Linus
 */

/*
 * Ok, demand-loading was easy, shared pages a little bit tricker. Shared
 * pages started 02.12.91, seems to work. - Linus.
 *
 * Tested sharing by executing about 30 /bin/sh: under the old kernel it
 * would have taken more than the 6M I have free, but it worked well as
 * far as I could see.
 *
 * Also corrected some "invalidate()"s - I wasn't doing enough of them.
 */
#include <stdarg.h>
#include <signal.h>
#include <asm/system.h>
#include <linux/sched.h>
#include <linux/head.h>
#include <linux/kernel.h>
#include <new.h>
#include <asm/segment.h>
volatile void do_exit(long code);

static inline volatile void oom(void)
{
	printk("out of memory\n\r");
	do_exit(SIGSEGV);
}

#define invalidate() \
__asm__("movl %%eax,%%cr3"::"a" (0))

/* these are not to be changed without changing head.s etc */
#define LOW_MEM 0x100000
#define PAGING_MEMORY (15*1024*1024)
#define PAGING_PAGES (PAGING_MEMORY>>12)
#define MAP_NR(addr) (((addr)-LOW_MEM)>>12)
#define USED 100

#define CODE_SPACE(addr) ((((addr)+4095)&~4095) < \
current->start_code + current->end_code)

static long HIGH_MEMORY = 0;

#define copy_page(from,to) \
__asm__("cld ; rep ; movsl"::"S" (from),"D" (to),"c" (1024))

static unsigned char mem_map [ PAGING_PAGES ] = {0,};

/*
 * Get physical address of first (actually last :-) free page, and mark it
 * used. If no free pages left, return 0.
 */
unsigned long get_free_page(void)
{
register unsigned long __res asm("ax");

__asm__("std ; repne ; scasb\n\t"
	"jne 1f\n\t"
	"movb $1,1(%%edi)\n\t"
	"sall $12,%%ecx\n\t"
	"addl %2,%%ecx\n\t"
	"movl %%ecx,%%edx\n\t"
	"movl $1024,%%ecx\n\t"
	"leal 4092(%%edx),%%edi\n\t"
	"rep ; stosl\n\t"
	"movl %%edx,%%eax\n\t"
	"1:"
	"cld\n\t"       /* by wyj */
	:"=a" (__res)
	:"0" (0),"i" (LOW_MEM),"c" (PAGING_PAGES),
	"D" (mem_map+PAGING_PAGES-1)
	);
return __res;
}

/*
 * Free a page of memory at physical address 'addr'. Used by
 * 'free_page_tables()'
 */
void free_page(unsigned long addr)
{
	if (addr < LOW_MEM) return;
	if (addr >= HIGH_MEMORY)
		panic("trying to free nonexistent page");
	addr -= LOW_MEM;
	addr >>= 12;
	if (mem_map[addr]--) return;
	mem_map[addr]=0;
	panic("trying to free free page");
}

/*
 * This function frees a continuos block of page tables, as needed
 * by 'exit()'. As does copy_page_tables(), this handles only 4Mb blocks.
 */
int free_page_tables(unsigned long from,unsigned long size)
{
	unsigned long *pg_table;
	unsigned long * dir, nr;

	if (from & 0x3fffff)
		panic("free_page_tables called with wrong alignment");
	if (!from)
		panic("Trying to free up swapper memory space");
	size = (size + 0x3fffff) >> 22;
	dir = (unsigned long *) ((from>>20) & 0xffc); /* _pg_dir = 0 */
	for ( ; size-->0 ; dir++) {
		if (!(1 & *dir))
			continue;
		pg_table = (unsigned long *) (0xfffff000 & *dir);
		for (nr=0 ; nr<1024 ; nr++) {
			if (1 & *pg_table)
				free_page(0xfffff000 & *pg_table);
			*pg_table = 0;
			pg_table++;
		}
		free_page(0xfffff000 & *dir);
		*dir = 0;
	}
	invalidate();
	return 0;
}

/*
 *  Well, here is one of the most complicated functions in mm. It
 * copies a range of linerar addresses by copying only the pages.
 * Let's hope this is bug-free, 'cause this one I don't want to debug :-)
 *
 * Note! We don't copy just any chunks of memory - addresses have to
 * be divisible by 4Mb (one page-directory entry), as this makes the
 * function easier. It's used only by fork anyway.
 *
 * NOTE 2!! When from==0 we are copying kernel space for the first
 * fork(). Then we DONT want to copy a full page-directory entry, as
 * that would lead to some serious memory waste - we just copy the
 * first 160 pages - 640kB. Even that is more than we need, but it
 * doesn't take any more memory - we don't copy-on-write in the low
 * 1 Mb-range, so the pages can be shared with the kernel. Thus the
 * special case for nr=xxxx.
 */
int copy_page_tables(unsigned long from,unsigned long to,long size )
{
	unsigned long * from_page_table;
	unsigned long * to_page_table;
	unsigned long this_page;
	unsigned long * from_dir, * to_dir;
	unsigned long nr;

	if ((from&0x3fffff) || (to&0x3fffff))
		panic("copy_page_tables called with wrong alignment");
	from_dir = (unsigned long *) ((from>>20) & 0xffc); /* _pg_dir = 0 */
	to_dir = (unsigned long *) ((to>>20) & 0xffc);
	size = ((unsigned) (size+0x3fffff)) >> 22;
	for( ; size-->0 ; from_dir++,to_dir++) {
		if (1 & *to_dir)
			panic("copy_page_tables: already exist");
		if (!(1 & *from_dir))
			continue;
		from_page_table = (unsigned long *) (0xfffff000 & *from_dir);
		if (!(to_page_table = (unsigned long *) get_free_page()))
			return -1;	/* Out of memory, see freeing */
		*to_dir = ((unsigned long) to_page_table) | 7;
		nr = (from==0)?0xA0:1024;
		for ( ; nr-- > 0 ; from_page_table++,to_page_table++) {
			this_page = *from_page_table;
			if (!(1 & this_page))
				continue;
			this_page &= ~2;
			*to_page_table = this_page;
			if (this_page > LOW_MEM) {
				*from_page_table = this_page;
				this_page -= LOW_MEM;
				this_page >>= 12;
				mem_map[this_page]++;
			}
		}
	}
	invalidate();
	return 0;
}

/*
 * This function puts a page in memory at the wanted address.
 * It returns the physical address of the page gotten, 0 if
 * out of memory (either when trying to access page-table or
 * page.)
 */
unsigned long put_page(unsigned long page,unsigned long address)
{
	unsigned long tmp, *page_table;

/* NOTE !!! This uses the fact that _pg_dir=0 */

	if (page < LOW_MEM || page >= HIGH_MEMORY)
		printk("Trying to put page %p at %p\n",page,address);
	if (mem_map[(page-LOW_MEM)>>12] != 1)
		printk("mem_map disagrees with %p at %p\n",page,address);
	page_table = (unsigned long *) ((address>>20) & 0xffc);
	if ((*page_table)&1)
		page_table = (unsigned long *) (0xfffff000 & *page_table);
	else {
		if (!(tmp=get_free_page()))
			return 0;
		*page_table = tmp|7;
		page_table = (unsigned long *) tmp;
	}
	page_table[(address>>12) & 0x3ff] = page | 7;
/* no need for invalidate */
	return page;
}

void un_wp_page(unsigned long * table_entry)
{
	unsigned long old_page,new_page;

	old_page = 0xfffff000 & *table_entry;
	if (old_page >= LOW_MEM && mem_map[MAP_NR(old_page)]==1) {
		*table_entry |= 2;
		invalidate();
		return;
	}
	if (!(new_page=get_free_page()))
		oom();
	if (old_page >= LOW_MEM)
		mem_map[MAP_NR(old_page)]--;
	*table_entry = new_page | 7;
	invalidate();
	copy_page(old_page,new_page);
}	

/*
 * This routine handles present pages, when users try to write
 * to a shared page. It is done by copying the page to a new address
 * and decrementing the shared-page counter for the old page.
 *
 * If it's in code space we exit with a segment error.
 */
void do_wp_page(unsigned long error_code,unsigned long address)
{
#if 0
/* we cannot do this yet: the estdio library writes to code space */
/* stupid, stupid. I really want the libc.a from GNU */
	if (CODE_SPACE(address))
		do_exit(SIGSEGV);
#endif
	un_wp_page((unsigned long *)
		(((address>>10) & 0xffc) + (0xfffff000 &
		*((unsigned long *) ((address>>20) &0xffc)))));

}

void write_verify(unsigned long address)
{
	unsigned long page;

	if (!( (page = *((unsigned long *) ((address>>20) & 0xffc)) )&1))
		return;
	page &= 0xfffff000;
	page += ((address>>10) & 0xffc);
	if ((3 & *(unsigned long *) page) == 1)  /* non-writeable, present */
		un_wp_page((unsigned long *) page);
	return;
}

void get_empty_page(unsigned long address)
{
	unsigned long tmp;

	if (!(tmp=get_free_page()) || !put_page(tmp,address)) {
		free_page(tmp);		/* 0 is ok - ignored */
		oom();
	}
}

/*
 * try_to_share() checks the page at address "address" in the task "p",
 * to see if it exists, and if it is clean. If so, share it with the current
 * task.
 *
 * NOTE! This assumes we have checked that p != current, and that they
 * share the same executable.
 */
static int try_to_share(unsigned long address, struct task_struct * p)
{
	unsigned long from;
	unsigned long to;
	unsigned long from_page;
	unsigned long to_page;
	unsigned long phys_addr;

	from_page = to_page = ((address>>20) & 0xffc);
	from_page += ((p->start_code>>20) & 0xffc);
	to_page += ((current->start_code>>20) & 0xffc);
/* is there a page-directory at from? */
	from = *(unsigned long *) from_page;
	if (!(from & 1))
		return 0;
	from &= 0xfffff000;
	from_page = from + ((address>>10) & 0xffc);
	phys_addr = *(unsigned long *) from_page;
/* is the page clean and present? */
	if ((phys_addr & 0x41) != 0x01)
		return 0;
	phys_addr &= 0xfffff000;
	if (phys_addr >= HIGH_MEMORY || phys_addr < LOW_MEM)
		return 0;
	to = *(unsigned long *) to_page;
	if (!(to & 1))
		if (to = get_free_page())
			*(unsigned long *) to_page = to | 7;
		else
			oom();
	to &= 0xfffff000;
	to_page = to + ((address>>10) & 0xffc);
	if (1 & *(unsigned long *) to_page)
		panic("try_to_share: to_page already exists");
/* share them: write-protect */
	*(unsigned long *) from_page &= ~2;
	*(unsigned long *) to_page = *(unsigned long *) from_page;
	invalidate();
	phys_addr -= LOW_MEM;
	phys_addr >>= 12;
	mem_map[phys_addr]++;
	return 1;
}


/*
 * share_page() tries to find a process that could share a page with
 * the current one. Address is the address of the wanted page relative
 * to the current data space.
 *
 * We first check if it is at all feasible by checking executable->i_count.
 * It should be >1 if there are other tasks sharing this inode.
 */
static int share_page(unsigned long address)
{
	struct task_struct ** p;

	if (!current->executable)
		return 0;
	if (current->executable->i_count < 2)
		return 0;
	for (p = &LAST_TASK ; p > &FIRST_TASK ; --p) {
		if (!*p)
			continue;
		if (current == *p)
			continue;
		if ((*p)->executable != current->executable)
			continue;
		if (try_to_share(address,*p))
			return 1;
	}
	return 0;
}

void do_no_page(unsigned long error_code,unsigned long address)
{
	int nr[4];
	unsigned long tmp;
	unsigned long page;
	int block,i;

	/* if (current->pid > 5)
		printk(" --do_no_page: address=%x, pid=%d\n", address, current->pid); */
		
	address &= 0xfffff000;
	tmp = address - current->start_code;
	if (!current->executable || tmp >= current->end_data) {
		get_empty_page(address);
		return;
	}
	if (share_page(tmp))
		return;
	if (!(page = get_free_page()))
		oom();
/* remember that 1 block is used for header */
	block = 1 + tmp/BLOCK_SIZE;
	for (i=0 ; i<4 ; block++,i++)
		nr[i] = bmap(current->executable,block);
	bread_page(page,current->executable->i_dev,nr);
	i = tmp + 4096 - current->end_data;
	tmp = page + 4096;
	while (i-- > 0) {
		tmp--;
		*(char *)tmp = 0;
	}
	if (put_page(page,address))
		return;
	free_page(page);
	oom();
}

void mem_init(long start_mem, long end_mem)
{
	int i;

	HIGH_MEMORY = end_mem;
	for (i=0 ; i<PAGING_PAGES ; i++)
		mem_map[i] = USED;
	i = MAP_NR(start_mem);
	end_mem -= start_mem;
	end_mem >>= 12;
	while (end_mem-->0)
		mem_map[i++]=0;
}

int do_execve2(unsigned long * eip,long tmp,char * filename,
	char ** argv, char ** envp)
{
	int ans=0;
	if((ans=do_execve(eip,tmp,filename,argv,envp)))
		return ans;
	int nr[4];
	unsigned long temp;
	unsigned long page;
	int block,i;
	unsigned long address=current->start_code;
	//this part comes from do_no_page as achievement of immediate loading of cs and ds
	while(address<=current->brk+current->start_code)
	{
		address &= 0xfffff000;
		temp = address - current->start_code;
		if (share_page(temp))
			return -1;
		if (!(page = get_free_page()))
			oom();
		block = 1 + temp/BLOCK_SIZE;
		for (i=0 ; i<4 ; block++,i++)
			nr[i] = bmap(current->executable,block);
		bread_page(page,current->executable->i_dev,nr);
		if (!put_page(page,address))
		{
			free_page(page);
			oom();
		}
		address+=PAGE_SIZE;
	}
	return 0;
}
void calc_mem(void)
{
	int i,j,k,free=0;
	long * pg_tbl;

	for(i=0 ; i<PAGING_PAGES ; i++)
		if (!mem_map[i]) free++;
	printk("%d pages free (of %d)\n\r",free,PAGING_PAGES);
	for(i=2 ; i<1024 ; i++) {
		if (1&pg_dir[i]) {
			pg_tbl=(long *) (0xfffff000 & pg_dir[i]);
			for(j=k=0 ; j<1024 ; j++)
				if (pg_tbl[j]&1)
					k++;
			printk("Pg-dir[%d] uses %d pages\n",i,k);
		}
	}
}

static int my_share(unsigned long address, struct task_struct * p)
{
	unsigned long from;
	unsigned long to;
	unsigned long from_page;
	unsigned long to_page;
	unsigned long phys_addr;

	from_page = to_page = ((address>>20) & 0xffc);
	from_page += ((current->start_code>>20) & 0xffc);
	to_page += ((p->start_code>>20) & 0xffc);

	from = *(unsigned long *) from_page;
	from &= 0xfffff000;
	from_page = from + ((address>>10) & 0xffc);
	phys_addr = *(unsigned long *) from_page;
	to = *(unsigned long *) to_page;
	if (!(to & 1))
		if (to = get_free_page())
			*(unsigned long *) to_page = to | 7;
		else
			return 0;
	to &= 0xfffff000;
	to_page = to + ((address>>10) & 0xffc);
	if (1 & *(unsigned long *) to_page)
		return 0;
	/* share them: write-protect */
	*(unsigned long *) to_page = *(unsigned long *) from_page;
	phys_addr -= LOW_MEM;
	phys_addr >>= 12;
	mem_map[phys_addr]++;
	return 1;
}

// rememeber to sync when munmap exit manual 

long sys_mmap(void * start,size_t len,...)// int prot,int flags,int fd,off_t off
{
	/* va_list args;
	va_start(args,len); */
	int prot=3,flags=2,fd=3,off=0;
	/* prot=va_arg(args,int);flags=va_arg(args,int);fd=va_arg(args,int);
	off_t off=va_arg(args,off_t);
	int *ll=&len;printk("%d,%d,%d,%d,%d\n",*ll,*(ll+1),*(ll+2),*(ll+3),*(ll+4));
	va_end(args);
	printk("%d,%d,%d,%ld\n",prot,flags,fd,off);
	 */
	int block;
	size_t l=len;
	struct buffer_head * bh;
	char *temp,*p1,*p2;
	void * buf=start;
	int tempprot=0;
	
	//因为new.h和namei.c定义不一样，要修改
	if(prot &PROT_READ) tempprot |=4;
	if(prot &PROT_EXEC) tempprot |=1;
	if(prot &PROT_WRITE) tempprot |=2;

	//特殊量len>0 off%4096==0 prot至少有read权限
	if( (flags & MAP_SHARED)&& (flags &MAP_PRIVATE )) 
	{
		printk("error with private and shared request.\n");
		return -1;
	}
	if(len<=0 ||  off<0 || (off%PAGE_SIZE)) 
	{
		if(len<=0) 
			printk("the len of the wanting bytes must be positive.\n");
		else
			printk("offset must be the mul of 4096.\n");
		return MAP_FAILED;
	}	
	if(!(prot& PROT_READ)) return MAP_FAILED;

	//permissions of the file ,搬运函数namei.c::permissions

	struct m_inode *inode=current->filp[fd]->f_inode;
	int mode = inode->i_mode;
	if (inode->i_dev && !inode->i_nlinks)
		return MAP_FAILED;
	else if (current->euid==inode->i_uid)
		mode >>= 6;
	else if (current->egid==inode->i_gid)
		mode >>= 3;
	if (!(((mode & tempprot & 0007) == tempprot) || suser()))
	{
		printk("error permission.");
		return MAP_FAILED;
	}
	//end of permission check
	
	//设置用户空间的虚拟地址，初始为32MB处，这样写在brk增长至32MB时会有bug,我们忽略
	//同时，当栈向下增长到一定程度时，也会和当前地址冲突，我们忽略
	if(start<=current->brk || start>=current->start_stack-0x8000 || start==NULL) 
	{
		if(!current->mmap_tail)
			buf=0x2000000;
		else
			buf=current->mmap_tail->endaddr;
	}
	//申请mmap
	struct mmap_struct *mmap=(struct mmap_struct *)malloc(sizeof(struct mmap_struct));
	mmap->address=buf;
	mmap->size=len;
	mmap->endaddr=(unsigned long)buf+(len + 0xfff)&0xfffff000;
	mmap->rw=prot;
	mmap->ps=flags;
	mmap->filenode=(struct m_inode*)malloc(sizeof(struct m_inode));
	memcpy(mmap->filenode,inode,sizeof(struct m_inode));
	if(!mmap->filenode->i_count)mmap->filenode->i_count=1;
	mmap->off=off;
	mmap->next=NULL;
	//加入current->mmap
	if(!current->mmap) 
		{current->mmap=current->mmap_tail=mmap;}
	else {
		current->mmap_tail->next=mmap;
		current->mmap_tail=mmap;
	}
	
	//分配物理页

	unsigned long from;
	unsigned long to;
	unsigned long from_page;
	unsigned long to_page;
	unsigned long phys_addr;
	unsigned long tpage;
	unsigned long address=mmap->address;
	while(address<mmap->endaddr)
	{
		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 MAP_FAILED;
			}
			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 MAP_FAILED;
			}
			else
			{
				*(unsigned long *)from_page= tpage | 7; 
				mem_map[(tpage-LOW_MEM)>>12]++;
			}
		*(unsigned long *)from_page &= (prot&PROT_WRITE)?0xffffffff:0xfffffffd; //分配读写权限
		
		if(flags & MAP_SHARED)
		{
			//printk("i am doing sharing.");
			struct task_struct ** p;

			for (p = &LAST_TASK ; p > &FIRST_TASK ; --p) {
				if (!*p)
					continue;
				if (current == *p)
					continue;
				//在这一部分,我将current->address处的物理页复制给
				//所有进程的该区域，可能导致错误，但我们忽略。
				if(!my_share(address,*p))
					printk("share failed at task:pid=%d",(*p)->pid);
			}
		}
		address+=PAGE_SIZE;
	}
		
	//read and put in 
	if (!(block = inode->i_zone[0]))
		return NULL;
	if (!(bh = bread(inode->i_dev,block)))
		return NULL;
	temp = (char *) bh->b_data;
	p1=temp+off;p2=buf;
	while(l--)
		put_fs_byte(*(p1++),p2++);
	return buf;
}
static int my_sync(off_t pos, struct m_inode * inode, char * buf, int count)
{
	int block,c;
	struct buffer_head * bh;
	char * p;
	int i=0;

	while (i<count) {
		if (!(block = create_block(inode,pos/BLOCK_SIZE)))
			break;
		if (!(bh=bread(inode->i_dev,block)))
			break;
		c = pos % BLOCK_SIZE;
		p = c + bh->b_data;
		bh->b_dirt = 1;
		c = BLOCK_SIZE-c;
		if (c > count-i) c = count-i;
		pos += c;
		if (pos > inode->i_size) {
			inode->i_size = pos;  
			inode->i_dirt = 1;
		}
		i += c;
		while (c-->0)
			*(p++) = get_fs_byte(buf++);
		brelse(bh);
	}
	inode->i_mtime = CURRENT_TIME;//文件最后修改时间
	inode->i_ctime = CURRENT_TIME;//i节点修改时间
	return (i?i:-1);
}


int sys_munmap(void * start ,size_t size)
{
	struct mmap_struct *temp=current->mmap;
	struct mmap_struct *pre=NULL;
	while(temp!=NULL)
	{
		if(temp->address==(unsigned long)start)
			break;
		else temp=temp->next;
		pre=temp;
	}
	if(!temp) 
	{
		printk("invalid address.\n");
		return -1;
	}
	if(!pre)
	{
		if(current->mmap_tail==current->mmap)current->mmap_tail=NULL;
		current->mmap=current->mmap->next;
	}
	else if(temp->next=NULL)
	{
		current->mmap_tail=pre;
		pre->next=NULL;
	}
	else{
		pre->next=temp->next;
	}
	unsigned long from;
	unsigned long to;
	unsigned long from_page;
	unsigned long to_page;
	unsigned long phys_addr;
	unsigned long tpage;
	unsigned long address=temp->address;
	printk("%lx\n",address);
	if(!(temp->ps & MAP_SHARED))
		goto mytag;
	//若为共享，执行下面的代码
	while (address < temp ->endaddr)
	{
		//printk("addr: %lx\n",address);
		from_page =  ((address>>20) & 0xffc);
		from_page += ((current->start_code>>20) & 0xffc);//页目录
		from=*(unsigned long *)from_page;	//页表项
		from &= 0xfffff000;
		from_page = from + ((address>>10) & 0xffc);
		phys_addr =	(*(unsigned long *)from_page & 0xfffff000);
		//printk("addr: %lx",*(unsigned long *)from_page);
		if(!(*(unsigned long *)from_page & 1))
		{
			printk("error of deleting page at %x.\n",*(unsigned long *)from_page);
			printk("current address:%x\n",address);
			return -1;
		}
		if(temp->ps & MAP_SHARED)
		{
			struct task_struct ** p;

			for (p = &LAST_TASK ; p > &FIRST_TASK ; --p) {
				if (!*p)
					continue;
				if (current == *p)
					continue;
				to_page = ((address>>20) & 0xffc)+(((*p)->start_code>>20) & 0xffc);
				to = *(unsigned long *) to_page;
				if(!(to & 1))
					continue;
				to &= 0xfffff000;
				to_page = to + ((address>>10) & 0xffc);
				if(!(*(unsigned long *)to_page &1)) 
					continue;
				to = (*(unsigned long *)to_page & 0xfffff000);
				if(phys_addr == to)
				{
					*(unsigned long *)to_page &= ~1;
					mem_map[(phys_addr-LOW_MEM)>>12]--;
				}
			}
		}
		address+=PAGE_SIZE;
	}
	if(temp->ps & MAP_SHARED)
	{
		if(my_sync(temp->off,temp->filenode,(char*)(temp->address),temp->size)==-1)
			return -1;
	}
mytag:
	//取消物理页写权限
	address=temp->address;
	while (address < temp ->endaddr)
	{
		//printk("%lx\n",address);
		from_page =  ((address>>20) & 0xffc);
		from_page += ((current->start_code>>20) & 0xffc);//页目录
		from=*(unsigned long *)from_page;	//页表项
		from &= 0xfffff000;
		from_page = from + ((address>>10) & 0xffc);
		phys_addr =	(*(unsigned long *)from_page & 0xfffff000);
		//printk("addr: %lx",*(unsigned long *)from_page);
		if(!(*(unsigned long *)from_page & 1))
		{
			printk("error of deleting page at %x.\n",*(unsigned long *)from_page);
			printk("current address:%x\n",address);
			return -1;
		}
		else{
			*(unsigned long *)from_page &= ~1;
		}
		address+=PAGE_SIZE;
	}
	free(temp->filenode);
	free(temp);
	return 0;
}



/*
	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;
} */
/*  child_stack-4 00 00 00 00 */																
	/*  child_stack-8 00 00 00 00 */
	/*  child_stack-12 arg */
	/*  child_stack-16 fn */		//esp
	/*  child_stack-20 00 00 00 00 */
	/*  child_stack-24 00 00 00 00 */
	/*  child_stack-28 00 00 00 00 */
	/*  child_stack-32 0x000000c3 */
/*
int do_clone(int nr,long tmp,int (*fn)(void *), void *child_stack, int flag) 
{
	void * argv =NULL;
	//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
	unsigned long nrfrom_page,nrfrom,from_page,from,tpage,address;
	address = task[nr]->tss.esp;
	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;
	unsigned long stack[128];
	unsigned long off=(unsigned long)child_stack & 0xfff;
	if(off < 32) 
	{
		printk("地址跨页,我也没办法.\n");
		return -1;
	}
		
 	//更新esp,让其指向child_stack同样偏移的地点;					
	//注意：这里child_stack 指向的是高地址，要向下面push.	
	task[nr]->tss.esp &=0xfffff000;		
	task[nr]->tss.esp |=off - 16;			
	//eip 只有一条ret  //所以传进来的fn必须以exit结尾，不能return ,	
	//因为我不会return这个玩意push ebp 又pop 啥的		
	task[nr]->tss.eip &=0xfffff000;	
	task[nr]->tss.eip |=off - 32;	
	 //ret	eip

	stack[0]=0x000000c3;
	stack[4]=(unsigned long)fn;
	stack[5]=(unsigned long)argv;									
	char * p1=stack, *p2=(unsigned long) child_stack - 32,len=32;
	while(len--)
		put_fs_byte(*(p1++),p2++);
	printk("nr:%d::fn:%x\n",nr,(unsigned long )fn);
	return 0;
}
*/
int copy_page_tables_clone(unsigned long from,unsigned long to,long size )
{
	unsigned long * from_page_table;
	unsigned long * to_page_table;
	unsigned long this_page;
	unsigned long * from_dir, * to_dir;
	unsigned long nr;

	if ((from&0x3fffff) || (to&0x3fffff))
		panic("copy_page_tables called with wrong alignment");
	from_dir = (unsigned long *) ((from>>20) & 0xffc); /* _pg_dir = 0 */
	to_dir = (unsigned long *) ((to>>20) & 0xffc);
	size = ((unsigned) (size+0x3fffff)) >> 22;
	for( ; size-->0 ; from_dir++,to_dir++) {
		if (1 & *to_dir)
			panic("copy_page_tables: already exist");
		if (!(1 & *from_dir))
			continue;
		from_page_table = (unsigned long *) (0xfffff000 & *from_dir);
		if (!(to_page_table = (unsigned long *) get_free_page()))
			return -1;	/* Out of memory, see freeing */
		*to_dir = ((unsigned long) to_page_table) | 7;
		nr = (from==0)?0xA0:1024;
		for ( ; nr-- > 0 ; from_page_table++,to_page_table++) {
			this_page = *from_page_table;
			if (!(1 & this_page))
				continue;
			*to_page_table = this_page;
			if (this_page > LOW_MEM) {
				*from_page_table = this_page;
				this_page -= LOW_MEM;
				this_page >>= 12;
				mem_map[this_page]++;
			}
		}
	}
	invalidate();
	return 0;
}