inode.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/inode.c
 *
 *  (C) 1991  Linus Torvalds
 */

#include <string.h>
#include "fs.h"

struct m_inode inode_table[NR_INODE]={{0,},};

static void read_inode(struct m_inode * inode);
static void write_inode(struct m_inode * inode);

static  void wait_on_inode(struct m_inode * inode)
{/*
	cli();
	while (inode->i_lock)
		sleep_on(&inode->i_wait);
	sti();
	*/
}

static  void lock_inode(struct m_inode * inode)
{
	/*
	cli();
	while (inode->i_lock)
		sleep_on(&inode->i_wait);
	inode->i_lock=1;
	sti();
	*/
}

static  void unlock_inode(struct m_inode * inode)
{
	/*
	inode->i_lock=0;
	wake_up(&inode->i_wait);
	*/
}

void invalidate_inodes(int dev)
{
	int i;
	struct m_inode * inode;

	inode = 0+inode_table;
	for(i=0 ; i<NR_INODE ; i++,inode++) {
		wait_on_inode(inode);
		if (inode->i_dev == dev) {
			if (inode->i_count)
				printk("inode in use on removed disk\n\r");
			inode->i_dev = inode->i_dirt = 0;
		}
	}
}

void sync_inodes(void)
{
	int i;
	struct m_inode * inode;

	inode = 0+inode_table;
	for(i=0 ; i<NR_INODE ; i++,inode++) {
		wait_on_inode(inode);
		if (inode->i_dirt && !inode->i_pipe)
			write_inode(inode);
	}
}

/*
inode: i节点指针
block: 文件中的block号，和磁盘上的block号不一样，这个号从文件头开始计数为0块，根据大小递增
create:创建标志
return value: 返回对应的磁盘上的block号
*/
static int _bmap(struct m_inode * inode,int block,int create)
{
	struct buffer_head * bh;
	int i;

	//block不能小于0。
	if (block<0)
		panic("_bmap: block<0");
	//不能超过最大的表示块数目
	if (block >= 7+512+512*512)
		panic("_bmap: block>big");


	//blcok<7,说明是在直接块中

	if (block<7) {

		//如果创建，并且该块内容为空
		if (create && !inode->i_zone[block])
			if (inode->i_zone[block]=new_block(inode->i_dev)) {
				inode->i_ctime=CURRENT_TIME;
				inode->i_dirt=1;
			}
		//搞定直接块
		return inode->i_zone[block];
	}


    
	block -= 7;

	//如此说来是一次间接块

	if (block<512) {

		//需要创建 一块存放间接块数据, 由于一个逻辑块号是2字节(unsigned short), 所以刚申请的块
		//能够存放1024/2=512个逻辑块号。
		if (create && !inode->i_zone[7])
			if (inode->i_zone[7]=new_block(inode->i_dev)) {
				inode->i_dirt=1;
				inode->i_ctime=CURRENT_TIME;
			}

		//创建不成功
		if (!inode->i_zone[7])
			return 0;


		//获得该块内容，改块全部存放逻辑块号
		if (!(bh = bread(inode->i_dev,inode->i_zone[7])))
			return 0;

        //i为需要处理的逻辑块号（主义下面强制转换）
		i = ((unsigned short *) (bh->b_data))[block];

        //为该逻辑块申请空间
		if (create && !i)
			if (i=new_block(inode->i_dev)) {
                //设置该块号为i
				((unsigned short *) (bh->b_data))[block]=i;
				bh->b_dirt=1;
			}
		brelse(bh);
		return i;


	}

	//二次间接块，处理同上了
	block -= 512;
	if (create && !inode->i_zone[8])
		if (inode->i_zone[8]=new_block(inode->i_dev)) {
			inode->i_dirt=1;
			inode->i_ctime=CURRENT_TIME;
		}
	if (!inode->i_zone[8])
		return 0;
	if (!(bh=bread(inode->i_dev,inode->i_zone[8])))
		return 0;
	i = ((unsigned short *)bh->b_data)[block>>9];
	if (create && !i)
		if (i=new_block(inode->i_dev)) {
			((unsigned short *) (bh->b_data))[block>>9]=i;
			bh->b_dirt=1;
		}
	brelse(bh);
	if (!i)
		return 0;
	if (!(bh=bread(inode->i_dev,i)))
		return 0;
	i = ((unsigned short *)bh->b_data)[block&511];
	if (create && !i)
		if (i=new_block(inode->i_dev)) {
			((unsigned short *) (bh->b_data))[block&511]=i;
			bh->b_dirt=1;
		}
	brelse(bh);
	return i;
}

int bmap(struct m_inode * inode,int block)
{
	return _bmap(inode,block,0);
}

int create_block(struct m_inode * inode, int block)
{
	return _bmap(inode,block,1);
}
		
void iput(struct m_inode * inode)
{
	if (!inode)
		return;
	wait_on_inode(inode);
	if (!inode->i_count)
		panic("iput: trying to free free inode");
	/*
	if (inode->i_pipe) {
		wake_up(&inode->i_wait);
		if (--inode->i_count)
			return;
		free_page(inode->i_size);
		inode->i_count=0;
		inode->i_dirt=0;
		inode->i_pipe=0;
		return;
	}
	*/
	if (!inode->i_dev) {
		inode->i_count--;
		return;
	}
	if (S_ISBLK(inode->i_mode)) {
		sync_dev(inode->i_zone[0]);
		wait_on_inode(inode);
	}
repeat:
	if (inode->i_count>1) {
		inode->i_count--;
		return;
	}
	if (!inode->i_nlinks) {
		truncate(inode);
		free_inode(inode);
		return;
	}
	if (inode->i_dirt) {
		write_inode(inode);	/* we can sleep - so do again */
		wait_on_inode(inode);
		goto repeat;
	}
	inode->i_count--;
	return;
}
//// 从i 节点表(inode_table)中获取一个空闲i 节点项。
// 寻找引用计数count 为0 的i 节点，并将其写盘后清零，返回其指针。
struct m_inode * get_empty_inode(void)
{
	struct m_inode * inode;
	static struct m_inode * last_inode = inode_table;
	int i;

	do {
		inode = NULL;
		for (i = NR_INODE; i ; i--) {
			if (++last_inode >= inode_table + NR_INODE)
				last_inode = inode_table;
			if (!last_inode->i_count) {
				inode = last_inode;
				if (!inode->i_dirt && !inode->i_lock)
					break;
			}
		}
		if (!inode) {
			for (i=0 ; i<NR_INODE ; i++)
				printk("%04x: %6d\t",inode_table[i].i_dev,
					inode_table[i].i_num);
			panic("No free inodes in mem");
		}
		wait_on_inode(inode);
		while (inode->i_dirt) {
			write_inode(inode);
			wait_on_inode(inode);
		}
	} while (inode->i_count);
	memset(inode,0,sizeof(*inode));
	inode->i_count = 1;
	return inode;
}
/*
struct m_inode * get_pipe_inode(void)
{
	struct m_inode * inode;

	if (!(inode = get_empty_inode()))
		return NULL;
	if (!(inode->i_size=get_free_page())) {
		inode->i_count = 0;
		return NULL;
	}
	inode->i_count = 2;	/* sum of readers/writers */
/*	PIPE_HEAD(*inode) = PIPE_TAIL(*inode) = 0;
	inode->i_pipe = 1;
	return inode;
}
*/

struct m_inode * iget(int dev,int nr)
{
	struct m_inode * inode, * empty;

	if (!dev)
		panic("iget with dev==0");

	//首先找一个空闲的inode,以备没找到之用。

	empty = get_empty_inode();
	inode = inode_table;

	while (inode < NR_INODE+inode_table) {
		if (inode->i_dev != dev || inode->i_num != nr) {
			inode++;
			continue;
		}
		wait_on_inode(inode);
		if (inode->i_dev != dev || inode->i_num != nr) {
			inode = inode_table;
			continue;
		}
		inode->i_count++;

		// 如果该i 节点是其它文件系统的安装点，则在超级块表中搜寻安装在此i 节点的超级块。如果没有
// 找到，则显示出错信息，并释放函数开始获取的空闲节点，返回该i 节点指针。
		
		if (inode->i_mount) {
			int i;

			for (i = 0 ; i<NR_SUPER ; i++)
				if (super_block[i].s_imount==inode)
					break;
			if (i >= NR_SUPER) {
				printk("Mounted inode hasn't got sb\n");
				if (empty)
					iput(empty);
				return inode;
			}
			iput(inode);
			dev = super_block[i].s_dev;
			nr = ROOT_INO;
			inode = inode_table;
			continue;
		}
		
		if (empty)
			iput(empty);
		return inode;
	}
	if (!empty)
		return (NULL);
	inode=empty;
	inode->i_dev = dev;
	inode->i_num = nr;
	read_inode(inode);
	return inode;
}

static void read_inode(struct m_inode * inode)
{
	struct super_block * sb;
	struct buffer_head * bh;
	int block;

	lock_inode(inode);
	if (!(sb=get_super(inode->i_dev)))
		panic("trying to read inode without dev");


	//该i 节点所在的逻辑块号 = (启动块+超级块) + i 节点位图占用的块数 + 逻辑块位图占用的块数 +
    // (i 节点号-1)/每块含有的i 节点数
	block = 2 + sb->s_imap_blocks + sb->s_zmap_blocks +
		(inode->i_num-1)/INODES_PER_BLOCK;


	//读入该块
	if (!(bh=bread(inode->i_dev,block)))
		panic("unable to read i-node block");

	//强制得到该内存区
	*(struct d_inode *)inode =
		((struct d_inode *)bh->b_data)
			[(inode->i_num-1)%INODES_PER_BLOCK];

	brelse(bh);
	unlock_inode(inode);
}

static void write_inode(struct m_inode * inode)
{
	struct super_block * sb;
	struct buffer_head * bh;
	int block;

	lock_inode(inode);
	if (!inode->i_dirt || !inode->i_dev) {
		unlock_inode(inode);
		return;
	}
	if (!(sb=get_super(inode->i_dev)))
		panic("trying to write inode without device");
	block = 2 + sb->s_imap_blocks + sb->s_zmap_blocks +
		(inode->i_num-1)/INODES_PER_BLOCK;
	if (!(bh=bread(inode->i_dev,block)))
		panic("unable to read i-node block");
	((struct d_inode *)bh->b_data)
		[(inode->i_num-1)%INODES_PER_BLOCK] =
			*(struct d_inode *)inode;
	bh->b_dirt=1;
	inode->i_dirt=0;
	brelse(bh);
	unlock_inode(inode);
}