diff --git a/buffer.c b/buffer.c
new file mode 100644
index 0000000..90a1032
--- /dev/null
+++ b/buffer.c
@@ -0,0 +1,446 @@
+/*
+ *  linux/fs/buffer.c
+ *
+ *  (C) 1991  Linus Torvalds
+ */
+
+/*
+ *  'buffer.c' implements the buffer-cache functions. Race-conditions have
+ * been avoided by NEVER letting a interrupt change a buffer (except for the
+ * data, of course), but instead letting the caller do it. NOTE! As interrupts
+ * can wake up a caller, some cli-sti sequences are needed to check for
+ * sleep-on-calls. These should be extremely quick, though (I hope).
+ */
+
+/*
+ * NOTE! There is one discordant note here: checking floppies for
+ * disk change. This is where it fits best, I think, as it should
+ * invalidate changed floppy-disk-caches.
+ */
+
+#include <stdarg.h>
+ 
+#include <linux/config.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <asm/system.h>
+#include <asm/io.h>
+#include <linux/fs.h>
+#include <asm/segment.h>
+
+#define NAME_MAX 255
+
+extern void put_super(int dev);
+extern void invalidate_inodes(int dev);
+
+extern int end;
+struct buffer_head * start_buffer = (struct buffer_head *) &end;
+struct buffer_head * hash_table[NR_HASH];
+static struct buffer_head * free_list;
+static struct task_struct * buffer_wait = NULL;
+int NR_BUFFERS = 0;
+
+/*coded by dj*/
+struct linux_dirent
+{
+	long d_ino; /* inode number 索引节点号 */
+	off_t d_off;  /* offset to this dirent 在目录文件中的偏移 */
+	unsigned short d_reclen; /* length of this d_name 文件名长 */
+	char d_name[NAME_MAX+1]; /* file name (null-terminated) 文件名，最长255字符 */
+};
+/*coded by dj*/
+
+static inline void wait_on_buffer(struct buffer_head * bh)
+{
+	cli();
+	while (bh->b_lock)
+		sleep_on(&bh->b_wait);
+	sti();
+}
+
+int sys_sync(void)
+{
+	int i;
+	struct buffer_head * bh;
+
+	sync_inodes();		/* write out inodes into buffers */
+	bh = start_buffer;
+	for (i=0 ; i<NR_BUFFERS ; i++,bh++) {
+		wait_on_buffer(bh);
+		if (bh->b_dirt)
+			ll_rw_block(WRITE,bh);
+	}
+	return 0;
+}
+
+int sync_dev(int dev)
+{
+	int i;
+	struct buffer_head * bh;
+
+	bh = start_buffer;
+	for (i=0 ; i<NR_BUFFERS ; i++,bh++) {
+		if (bh->b_dev != dev)
+			continue;
+		wait_on_buffer(bh);
+		if (bh->b_dev == dev && bh->b_dirt)
+			ll_rw_block(WRITE,bh);
+	}
+	sync_inodes();
+	bh = start_buffer;
+	for (i=0 ; i<NR_BUFFERS ; i++,bh++) {
+		if (bh->b_dev != dev)
+			continue;
+		wait_on_buffer(bh);
+		if (bh->b_dev == dev && bh->b_dirt)
+			ll_rw_block(WRITE,bh);
+	}
+	return 0;
+}
+
+void inline invalidate_buffers(int dev)
+{
+	int i;
+	struct buffer_head * bh;
+
+	bh = start_buffer;
+	for (i=0 ; i<NR_BUFFERS ; i++,bh++) {
+		if (bh->b_dev != dev)
+			continue;
+		wait_on_buffer(bh);
+		if (bh->b_dev == dev)
+			bh->b_uptodate = bh->b_dirt = 0;
+	}
+}
+
+/*
+ * This routine checks whether a floppy has been changed, and
+ * invalidates all buffer-cache-entries in that case. This
+ * is a relatively slow routine, so we have to try to minimize using
+ * it. Thus it is called only upon a 'mount' or 'open'. This
+ * is the best way of combining speed and utility, I think.
+ * People changing diskettes in the middle of an operation deserve
+ * to loose :-)
+ *
+ * NOTE! Although currently this is only for floppies, the idea is
+ * that any additional removable block-device will use this routine,
+ * and that mount/open needn't know that floppies/whatever are
+ * special.
+ */
+void check_disk_change(int dev)
+{
+	int i;
+
+	if (MAJOR(dev) != 2)
+		return;
+	if (!floppy_change(dev & 0x03))
+		return;
+	for (i=0 ; i<NR_SUPER ; i++)
+		if (super_block[i].s_dev == dev)
+			put_super(super_block[i].s_dev);
+	invalidate_inodes(dev);
+	invalidate_buffers(dev);
+}
+
+#define _hashfn(dev,block) (((unsigned)(dev^block))%NR_HASH)
+#define hash(dev,block) hash_table[_hashfn(dev,block)]
+
+static inline void remove_from_queues(struct buffer_head * bh)
+{
+/* remove from hash-queue */
+	if (bh->b_next)
+		bh->b_next->b_prev = bh->b_prev;
+	if (bh->b_prev)
+		bh->b_prev->b_next = bh->b_next;
+	if (hash(bh->b_dev,bh->b_blocknr) == bh)
+		hash(bh->b_dev,bh->b_blocknr) = bh->b_next;
+/* remove from free list */
+	if (!(bh->b_prev_free) || !(bh->b_next_free))
+		panic("Free block list corrupted");
+	bh->b_prev_free->b_next_free = bh->b_next_free;
+	bh->b_next_free->b_prev_free = bh->b_prev_free;
+	if (free_list == bh)
+		free_list = bh->b_next_free;
+}
+
+static inline void insert_into_queues(struct buffer_head * bh)
+{
+/* put at end of free list */
+	bh->b_next_free = free_list;
+	bh->b_prev_free = free_list->b_prev_free;
+	free_list->b_prev_free->b_next_free = bh;
+	free_list->b_prev_free = bh;
+/* put the buffer in new hash-queue if it has a device */
+	bh->b_prev = NULL;
+	bh->b_next = NULL;
+	if (!bh->b_dev)
+		return;
+	bh->b_next = hash(bh->b_dev,bh->b_blocknr);
+	hash(bh->b_dev,bh->b_blocknr) = bh;
+	bh->b_next->b_prev = bh;
+}
+
+static struct buffer_head * find_buffer(int dev, int block)
+{		
+	struct buffer_head * tmp;
+
+	for (tmp = hash(dev,block) ; tmp != NULL ; tmp = tmp->b_next)
+		if (tmp->b_dev==dev && tmp->b_blocknr==block)
+			return tmp;
+	return NULL;
+}
+
+/*
+ * Why like this, I hear you say... The reason is race-conditions.
+ * As we don't lock buffers (unless we are readint them, that is),
+ * something might happen to it while we sleep (ie a read-error
+ * will force it bad). This shouldn't really happen currently, but
+ * the code is ready.
+ */
+struct buffer_head * get_hash_table(int dev, int block)
+{
+	struct buffer_head * bh;
+
+	for (;;) {
+		if (!(bh=find_buffer(dev,block)))
+			return NULL;
+		bh->b_count++;
+		wait_on_buffer(bh);
+		if (bh->b_dev == dev && bh->b_blocknr == block)
+			return bh;
+		bh->b_count--;
+	}
+}
+
+/*
+ * Ok, this is getblk, and it isn't very clear, again to hinder
+ * race-conditions. Most of the code is seldom used, (ie repeating),
+ * so it should be much more efficient than it looks.
+ *
+ * The algoritm is changed: hopefully better, and an elusive bug removed.
+ */
+#define BADNESS(bh) (((bh)->b_dirt<<1)+(bh)->b_lock)
+struct buffer_head * getblk(int dev,int block)
+{
+	struct buffer_head * tmp, * bh;
+
+repeat:
+	if (bh = get_hash_table(dev,block))
+		return bh;
+	tmp = free_list;
+	do {
+		if (tmp->b_count)
+			continue;
+		if (!bh || BADNESS(tmp)<BADNESS(bh)) {
+			bh = tmp;
+			if (!BADNESS(tmp))
+				break;
+		}
+/* and repeat until we find something good */
+	} while ((tmp = tmp->b_next_free) != free_list);
+	if (!bh) {
+		sleep_on(&buffer_wait);
+		goto repeat;
+	}
+	wait_on_buffer(bh);
+	if (bh->b_count)
+		goto repeat;
+	while (bh->b_dirt) {
+		sync_dev(bh->b_dev);
+		wait_on_buffer(bh);
+		if (bh->b_count)
+			goto repeat;
+	}
+/* NOTE!! While we slept waiting for this block, somebody else might */
+/* already have added "this" block to the cache. check it */
+	if (find_buffer(dev,block))
+		goto repeat;
+/* OK, FINALLY we know that this buffer is the only one of it's kind, */
+/* and that it's unused (b_count=0), unlocked (b_lock=0), and clean */
+	bh->b_count=1;
+	bh->b_dirt=0;
+	bh->b_uptodate=0;
+	remove_from_queues(bh);
+	bh->b_dev=dev;
+	bh->b_blocknr=block;
+	insert_into_queues(bh);
+	return bh;
+}
+
+void brelse(struct buffer_head * buf)
+{
+	if (!buf)
+		return;
+	wait_on_buffer(buf);
+	if (!(buf->b_count--))
+		panic("Trying to free free buffer");
+	wake_up(&buffer_wait);
+}
+
+/*
+ * bread() reads a specified block and returns the buffer that contains
+ * it. It returns NULL if the block was unreadable.
+ */
+struct buffer_head * bread(int dev,int block)
+{
+	struct buffer_head * bh;
+
+	if (!(bh=getblk(dev,block)))
+		panic("bread: getblk returned NULL\n");
+	if (bh->b_uptodate)
+		return bh;
+	ll_rw_block(READ,bh);
+	wait_on_buffer(bh);
+	if (bh->b_uptodate)
+		return bh;
+	brelse(bh);
+	return NULL;
+}
+
+#define COPYBLK(from,to) \
+__asm__("cld\n\t" \
+	"rep\n\t" \
+	"movsl\n\t" \
+	::"c" (BLOCK_SIZE/4),"S" (from),"D" (to) \
+	)
+
+/*
+ * bread_page reads four buffers into memory at the desired address. It's
+ * a function of its own, as there is some speed to be got by reading them
+ * all at the same time, not waiting for one to be read, and then another
+ * etc.
+ */
+void bread_page(unsigned long address,int dev,int b[4])
+{
+	struct buffer_head * bh[4];
+	int i;
+
+	for (i=0 ; i<4 ; i++)
+		if (b[i]) {
+			if (bh[i] = getblk(dev,b[i]))
+				if (!bh[i]->b_uptodate)
+					ll_rw_block(READ,bh[i]);
+		} else
+			bh[i] = NULL;
+	for (i=0 ; i<4 ; i++,address += BLOCK_SIZE)
+		if (bh[i]) {
+			wait_on_buffer(bh[i]);
+			if (bh[i]->b_uptodate)
+				COPYBLK((unsigned long) bh[i]->b_data,address);
+			brelse(bh[i]);
+		}
+}
+
+/*
+ * Ok, breada can be used as bread, but additionally to mark other
+ * blocks for reading as well. End the argument list with a negative
+ * number.
+ */
+struct buffer_head * breada(int dev,int first, ...)
+{
+	va_list args;
+	struct buffer_head * bh, *tmp;
+
+	va_start(args,first);
+	if (!(bh=getblk(dev,first)))
+		panic("bread: getblk returned NULL\n");
+	if (!bh->b_uptodate)
+		ll_rw_block(READ,bh);
+	while ((first=va_arg(args,int))>=0) {
+		tmp=getblk(dev,first);
+		if (tmp) {
+			if (!tmp->b_uptodate)
+				ll_rw_block(READA,bh);
+			tmp->b_count--;
+		}
+	}
+	va_end(args);
+	wait_on_buffer(bh);
+	if (bh->b_uptodate)
+		return bh;
+	brelse(bh);
+	return (NULL);
+}
+
+void buffer_init(long buffer_end)
+{
+	struct buffer_head * h = start_buffer;
+	void * b;
+	int i;
+
+	if (buffer_end == 1<<20)
+		b = (void *) (640*1024);
+	else
+		b = (void *) buffer_end;
+	while ( (b -= BLOCK_SIZE) >= ((void *) (h+1)) ) {
+		h->b_dev = 0;
+		h->b_dirt = 0;
+		h->b_count = 0;
+		h->b_lock = 0;
+		h->b_uptodate = 0;
+		h->b_wait = NULL;
+		h->b_next = NULL;
+		h->b_prev = NULL;
+		h->b_data = (char *) b;
+		h->b_prev_free = h-1;
+		h->b_next_free = h+1;
+		h++;
+		NR_BUFFERS++;
+		if (b == (void *) 0x100000)
+			b = (void *) 0xA0000;
+	}
+	h--;
+	free_list = start_buffer;
+	free_list->b_prev_free = h;
+	h->b_next_free = free_list;
+	for (i=0;i<NR_HASH;i++)
+		hash_table[i]=NULL;
+}	
+
+/*coded by dj */
+int sys_getdents(unsigned int fd, struct linux_dirent *dirp, unsigned int count)
+{
+	struct file *file;
+	struct m_inode *f_inode; 
+	struct linux_dirent my_dirent;	
+	struct buffer_head *block;
+	struct dir_entry *dir;		/*目录项地址*/
+	char *buf;
+	int byte = 0;			/*读取字节数*/
+	file = current->filp[fd]; /*读取的文件*/
+	if (!count)
+		return -1;	/*失败返回-1*/
+
+	f_inode = file->f_inode; /*文件的索引节点*/
+	block = bread(f_inode->i_dev, f_inode->i_zone[0]);
+
+	int k; /*已读到的位置*/
+	int len_dir = sizeof(struct dir_entry);
+	int len_dirent = sizeof(struct linux_dirent);
+	for (k = 0; k < f_inode->i_size; k += len_dir)
+	{
+		if (byte + len_dirent >= count)  /*到目录结尾返回0*/
+			return 0;
+
+		dir = (struct dir_entry *)(block->b_data + k);	/*获取目录项*/
+		if (dir->inode)		/*将要写入缓冲区的数据存好*/
+		{
+			my_dirent.d_ino = dir->inode;
+			int i;
+			for (i = 0; i < NAME_LEN; i++)	
+				my_dirent.d_name[i] = dir->name[i];
+			my_dirent.d_off = 0;
+			my_dirent.d_reclen = sizeof(my_dirent);
+			buf = &my_dirent;
+			for (i = 0; i < my_dirent.d_reclen; i++)
+			{
+				put_fs_byte(*(buf + i), ((char *)dirp) + i + byte); /*将用户态数据传入内核*/
+			}
+			byte += my_dirent.d_reclen;
+		}
+		else
+			continue;	/*空目录跳过*/
+	}
+	return byte;
+}
+/*coded by dj */