super.c

在VC平台下调试通过的linux 0.11文件系统代码！ 对学习文件系统实现的朋友很有帮助

/*
 *  linux/fs/super.c
 *
 *  (C) 1991  Linus Torvalds
 */

/*
 * super.c contains code to handle the super-block tables.
 */

#include "errno.h"
#include "fs.h"

int sync_dev(int dev);
void wait_for_keypress(void);

/* set_bit uses setb, as gas doesn't recognize setc */
static int set_bit(int bitnr, char * addr)
{
	char * p;
	int t,x;
	p = addr + bitnr/8;
	x = *p;
	t = 1 &(x >> bitnr%8);
	return t;
}
//#define set_bit(bitnr,addr) 1
/*
#define set_bit(bitnr,addr) ({ \
register int __res __asm__("ax"); \
__asm__("bt %2,%3;setb %%al":"=a" (__res):"a" (0),"r" (bitnr),"m" (*(addr))); \
__res; })
*/
//存放super_block 的内存，NR_SUPER 在fs.h中定义为8，可以根据实际情况修改
struct super_block super_block[NR_SUPER];
/* this is initialized in init/main.c */
int ROOT_DEV = 0;

static void lock_super(struct super_block * sb)
{
	/*
	cli();
	while (sb->s_lock)
		sleep_on(&(sb->s_wait));
	sb->s_lock = 1;
	sti();
	*/
}

static void free_super(struct super_block * sb)
{
	/*
	cli();
	sb->s_lock = 0;
	wake_up(&(sb->s_wait));
	sti();
	*/
}

static void wait_on_super(struct super_block * sb)
{
	/*
	cli();
	while (sb->s_lock)
		sleep_on(&(sb->s_wait));
	sti();
	*/
}

struct super_block * get_super(int dev)
{
	struct super_block * s;

	if (!dev)
		return NULL;
	s = 0+super_block;
	while (s < NR_SUPER+super_block)
		if (s->s_dev == dev) {
			wait_on_super(s);
			if (s->s_dev == dev)
				return s;
			s = 0+super_block;
		} else
			s++;
	return NULL;
}

void put_super(int dev)
{
	struct super_block * sb;
	struct m_inode * inode;
	int i;

	if (dev == ROOT_DEV) {
		printk("root diskette changed: prepare for armageddon\n\r");
		return;
	}
	if (!(sb = get_super(dev)))
		return;
	if (sb->s_imount) {
		printk("Mounted disk changed - tssk, tssk\n\r");
		return;
	}
	lock_super(sb);

	//放弃该块
	sb->s_dev = 0;

	//然后释放该设备i 节点位图和逻辑块位图在缓冲区中所占用的缓冲块。
	for(i=0;i<I_MAP_SLOTS;i++)
		brelse(sb->s_imap[i]);
	for(i=0;i<Z_MAP_SLOTS;i++)
		brelse(sb->s_zmap[i]);
	free_super(sb);
	return;
}

static struct super_block * read_super(int dev)
{
	struct super_block * s;
	struct buffer_head * bh;
	int i,block;

	if (!dev)
		return NULL;


	//已经存在了
	if (s = get_super(dev))
		return s;

	//寻找一个空的结构体
	for (s = 0+super_block ;; s++) {
		if (s >= NR_SUPER+super_block)
			return NULL;
		if (!s->s_dev)
			break;
	}


	s->s_dev = dev;
	s->s_isup = NULL;
	s->s_imount = NULL;
	s->s_time = 0;
	s->s_rd_only = 0;
	s->s_dirt = 0;
	lock_super(s);

	//读入第一块(即磁盘上的super_block)
	if (!(bh = bread(dev,1))) {
		s->s_dev=0;
		free_super(s);
		return NULL;
	}

	//那个数据就是superblock,强制转换之
	*((struct d_super_block *) s) =
		*((struct d_super_block *) bh->b_data);
	brelse(bh);

	//判断文件系统
	if (s->s_magic != SUPER_MAGIC) {
		s->s_dev = 0;
		free_super(s);
		return NULL;
	}

	//初始化inode bitmap, block bitmap
	for (i=0;i<I_MAP_SLOTS;i++)
		s->s_imap[i] = NULL;
	for (i=0;i<Z_MAP_SLOTS;i++)
		s->s_zmap[i] = NULL;



	//按照分区顺序,先读inode bitmap

	block=2;
	for (i=0 ; i < s->s_imap_blocks ; i++)
		if (s->s_imap[i]=bread(dev,block))
			block++;
		else
			break;

    //接着存放的就是block bitmap
	for (i=0 ; i < s->s_zmap_blocks ; i++)
		if (s->s_zmap[i]=bread(dev,block))
			block++;
		else
			break;


//    如果读出的位图逻辑块数不等于位图应该占有的逻辑块数，说明文件系统位图信息有问题，超级块
// 初始化失败。因此只能释放前面申请的所有资源，返回空指针并退出
	if (block != 2+s->s_imap_blocks+s->s_zmap_blocks) {
		for(i=0;i<I_MAP_SLOTS;i++)
			brelse(s->s_imap[i]);
		for(i=0;i<Z_MAP_SLOTS;i++)
			brelse(s->s_zmap[i]);
		s->s_dev=0;
		free_super(s);
		return NULL;
	}

	//0号位图(inode,block)不能使用,设置为1!
	s->s_imap[0]->b_data[0] |= 1;
	s->s_zmap[0]->b_data[0] |= 1;
	free_super(s);
	return s;
}
int sys_umount_dev(int dev)
{
	struct m_inode * inode;
	struct super_block * sb;


	if (!(sb=get_super(dev)) || !(sb->s_imount))
		return -ENOENT;
	if (!sb->s_imount->i_mount)
		printk("Mounted inode has i_mount=0\n");
	for (inode=inode_table+0 ; inode<inode_table+NR_INODE ; inode++)
		if (inode->i_dev==dev && inode->i_count)
				return -EBUSY;


	sb->s_imount->i_mount=0;
	iput(sb->s_imount);
	sb->s_imount = NULL;
	iput(sb->s_isup);
	sb->s_isup = NULL;
	put_super(dev);
	sync_dev(dev);
	return 0;

}
int sys_umount(char * dev_name)
{
	struct m_inode * inode;
	struct super_block * sb;
	int dev;

	if (!(inode=namei(dev_name)))
		return -ENOENT;
	dev = inode->i_zone[0];
	if (!S_ISBLK(inode->i_mode)) {
		iput(inode);
		return -ENOTBLK;
	}
	iput(inode);
	if (dev==ROOT_DEV)
		return -EBUSY;
	if (!(sb=get_super(dev)) || !(sb->s_imount))
		return -ENOENT;
	if (!sb->s_imount->i_mount)
		printk("Mounted inode has i_mount=0\n");
	for (inode=inode_table+0 ; inode<inode_table+NR_INODE ; inode++)
		if (inode->i_dev==dev && inode->i_count)
				return -EBUSY;
	sb->s_imount->i_mount=0;
	iput(sb->s_imount);
	sb->s_imount = NULL;
	iput(sb->s_isup);
	sb->s_isup = NULL;
	put_super(dev);
	sync_dev(dev);
	return 0;
}
/*
int sys_mount(char * dev_name, char * dir_name, int rw_flag)
{
	struct m_inode * dev_i, * dir_i;
	struct super_block * sb;
	int dev;

	if (!(dev_i=namei(dev_name)))
		return -ENOENT;
	dev = dev_i->i_zone[0];
	if (!S_ISBLK(dev_i->i_mode)) {
		iput(dev_i);
		return -EPERM;
	}
	iput(dev_i);
	if (!(dir_i=namei(dir_name)))
		return -ENOENT;
	if (dir_i->i_count != 1 || dir_i->i_num == ROOT_INO) {
		iput(dir_i);
		return -EBUSY;
	}
	if (!S_ISDIR(dir_i->i_mode)) {
		iput(dir_i);
		return -EPERM;
	}
	if (!(sb=read_super(dev))) {
		iput(dir_i);
		return -EBUSY;
	}
	if (sb->s_imount) {
		iput(dir_i);
		return -EBUSY;
	}
	if (dir_i->i_mount) {
		iput(dir_i);
		return -EPERM;
	}
	sb->s_imount=dir_i;
	dir_i->i_mount=1;
	dir_i->i_dirt=1;		
	return 0;			
}
*/

//加载根文件系统
void mount_root(void)
{
	int i,free;
	struct super_block * p;
	struct m_inode * mi;

	//防止源代码修改不一致
	if (32 != sizeof (struct d_inode))
		panic("bad i-node size");


	//初始化文件表
	for(i=0;i<NR_FILE;i++)
		file_table[i].f_count=0;
	if (MAJOR(ROOT_DEV) == 2) {
		printk("Insert root floppy and press ENTER");

	}


	for(p = &super_block[0] ; p < &super_block[NR_SUPER] ; p++) {
		p->s_dev = 0;
		p->s_lock = 0;
		p->s_wait = NULL;
	}

	if (!(p=read_super(ROOT_DEV)))
		panic("Unable to mount root");
	if (!(mi=iget(ROOT_DEV,ROOT_INO)))
		panic("Unable to read root i-node");

	mi->i_count += 3 ;	/* NOTE! it is logically used 4 times, not 1 */
	p->s_isup = p->s_imount = mi;
//	current->pwd = mi;
//	current->root = mi;
	free=0;
	i=p->s_nzones;
	while (-- i >= 0)
		if (!set_bit(i&8191,p->s_zmap[i>>13]->b_data))
			free++;
	printk("%d/%d free blocks\n\r",free,p->s_nzones);
	free=0;
	i=p->s_ninodes+1;
	while (-- i >= 0)
		if (!set_bit(i&8191,p->s_imap[i>>13]->b_data))
			free++;
	printk("%d/%d free inodes\n\r",free,p->s_ninodes);
}