namei.c

LINUX1.0内核源代码,学习LINUX编程的一定要看。

/*
 *  linux/fs/ext/namei.c
 *
 *  Copyright (C) 1992  Remy Card ([e-mail])
 *
 *  from
 *
 *  linux/fs/minix/namei.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/sched.h>
#include <linux/ext_fs.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/fcntl.h>
#include <linux/errno.h>

#include <asm/segment.h>

/*
 * comment out this line if you want names > EXT_NAME_LEN chars to be
 * truncated. Else they will be disallowed.
 */
/* #define NO_TRUNCATE */

/*
 * EXT_DIR_PAD defines the directory entries boundaries
 *
 * NOTE: It must be a power of 2 and must be greater or equal than 8
 * because a directory entry needs 8 bytes for its fixed part
 * (4 bytes for the inode, 2 bytes for the entry length and 2 bytes
 * for the name length)
 */
#define EXT_DIR_PAD 8

/*
 *
 * EXT_DIR_MIN_SIZE is the minimal size of a directory entry
 *
 * During allocations, a directory entry is split into 2 ones
 * *ONLY* if the size of the unused part is greater than or 
 * equal to EXT_DIR_MIN_SIZE
 */
#define EXT_DIR_MIN_SIZE 12

/*
 * ok, we cannot use strncmp, as the name is not in our data space.
 * Thus we'll have to use ext_match. No big problem. Match also makes
 * some sanity tests.
 *
 * NOTE! unlike strncmp, ext_match returns 1 for success, 0 for failure.
 */
static int ext_match(int len,const char * name,struct ext_dir_entry * de)
{
	register int same __asm__("ax");

	if (!de || !de->inode || len > EXT_NAME_LEN)
		return 0;
	/* "" means "." ---> so paths like "/usr/lib//libc.a" work */
	if (!len && (de->name[0]=='.') && (de->name[1]=='\0'))
		return 1;
	if (len < EXT_NAME_LEN && len != de->name_len)
		return 0;
	__asm__("cld\n\t"
		"repe ; cmpsb\n\t"
		"setz %%al"
		:"=a" (same)
		:"0" (0),"S" ((long) name),"D" ((long) de->name),"c" (len)
		:"cx","di","si");
	return same;
}

/*
 *	ext_find_entry()
 *
 * finds an entry in the specified directory with the wanted name. It
 * returns the cache buffer in which the entry was found, and the entry
 * itself (as a parameter - res_dir). It does NOT read the inode of the
 * entry - you'll have to do that yourself if you want to.
 *
 * addition for the ext file system : this function returns the previous
 * and next directory entries in the parameters prev_dir and next_dir
 */
static struct buffer_head * ext_find_entry(struct inode * dir,
	const char * name, int namelen, struct ext_dir_entry ** res_dir,
	struct ext_dir_entry ** prev_dir, struct ext_dir_entry ** next_dir)
{
	long offset;
	struct buffer_head * bh;
	struct ext_dir_entry * de;

	*res_dir = NULL;
	if (!dir)
		return NULL;
#ifdef NO_TRUNCATE
	if (namelen > EXT_NAME_LEN)
		return NULL;
#else
	if (namelen > EXT_NAME_LEN)
		namelen = EXT_NAME_LEN;
#endif
	bh = ext_bread(dir,0,0);
	if (!bh)
		return NULL;
	if (prev_dir)
		*prev_dir = NULL;
	if (next_dir)
		*next_dir = NULL;
	offset = 0;
	de = (struct ext_dir_entry *) bh->b_data;
	while (offset < dir->i_size) {
		if ((char *)de >= BLOCK_SIZE+bh->b_data) {
			brelse(bh);
			bh = NULL;
			bh = ext_bread(dir,offset>>BLOCK_SIZE_BITS,0);
			if (!bh)
				continue;
			de = (struct ext_dir_entry *) bh->b_data;
			if (prev_dir)
				*prev_dir = NULL;
		}
		if (de->rec_len < 8 || de->rec_len % 8 != 0 ||
		    de->rec_len < de->name_len + 8 ||
		    (((char *) de) + de->rec_len-1 >= BLOCK_SIZE+bh->b_data)) {
			printk ("ext_find_entry: bad dir entry\n");
			printk ("dev=%d, dir=%d, offset=%d, rec_len=%d, name_len=%d\n",
				dir->i_dev, dir->i_ino, offset, de->rec_len, de->name_len);
			de = (struct ext_dir_entry *) (bh->b_data+BLOCK_SIZE);
			offset = ((offset / BLOCK_SIZE) + 1) * BLOCK_SIZE;
			continue;
/*			brelse (bh);
			return NULL; */
		}
		if (ext_match(namelen,name,de)) {
			*res_dir = de;
			if (next_dir)
				if (offset + de->rec_len < dir->i_size &&
				    ((char *)de) + de->rec_len < BLOCK_SIZE+bh->b_data)
					*next_dir = (struct ext_dir_entry *)
						((char *) de + de->rec_len);
				else
					*next_dir = NULL;
			return bh;
		}
		offset += de->rec_len;
		if (prev_dir)
			*prev_dir = de;
		de = (struct ext_dir_entry *) ((char *) de + de->rec_len);
	}
	brelse(bh);
	return NULL;
}

int ext_lookup(struct inode * dir,const char * name, int len,
	struct inode ** result)
{
	int ino;
	struct ext_dir_entry * de;
	struct buffer_head * bh;

	*result = NULL;
	if (!dir)
		return -ENOENT;
	if (!S_ISDIR(dir->i_mode)) {
		iput(dir);
		return -ENOENT;
	}
	if (!(bh = ext_find_entry(dir,name,len,&de,NULL,NULL))) {
		iput(dir);
		return -ENOENT;
	}
	ino = de->inode;
	brelse(bh);
	if (!(*result = iget(dir->i_sb,ino))) {
		iput(dir);
		return -EACCES;
	}
	iput(dir);
	return 0;
}

/*
 *	ext_add_entry()
 *
 * adds a file entry to the specified directory, using the same
 * semantics as ext_find_entry(). It returns NULL if it failed.
 *
 * NOTE!! The inode part of 'de' is left at 0 - which means you
 * may not sleep between calling this and putting something into
 * the entry, as someone else might have used it while you slept.
 */
static struct buffer_head * ext_add_entry(struct inode * dir,
	const char * name, int namelen, struct ext_dir_entry ** res_dir)
{
	int i;
	long offset;
	unsigned short rec_len;
	struct buffer_head * bh;
	struct ext_dir_entry * de, * de1;

	*res_dir = NULL;
	if (!dir)
		return NULL;
#ifdef NO_TRUNCATE
	if (namelen > EXT_NAME_LEN)
		return NULL;
#else
	if (namelen > EXT_NAME_LEN)
		namelen = EXT_NAME_LEN;
#endif
	if (!namelen)
		return NULL;
	bh = ext_bread(dir,0,0);
	if (!bh)
		return NULL;
	rec_len = ((8 + namelen + EXT_DIR_PAD - 1) / EXT_DIR_PAD) * EXT_DIR_PAD;
	offset = 0;
	de = (struct ext_dir_entry *) bh->b_data;
	while (1) {
		if ((char *)de >= BLOCK_SIZE+bh->b_data && offset < dir->i_size) {
#ifdef EXTFS_DEBUG
printk ("ext_add_entry: skipping to next block\n");
#endif
			brelse(bh);
			bh = NULL;
			bh = ext_bread(dir,offset>>BLOCK_SIZE_BITS,0);
			if (!bh)
				return NULL;
			de = (struct ext_dir_entry *) bh->b_data;
		}
		if (offset >= dir->i_size) {
			/* Check that the directory entry fits in the block */
			if (offset % BLOCK_SIZE == 0  ||
			    (BLOCK_SIZE - (offset % BLOCK_SIZE)) < rec_len) {
				if ((offset % BLOCK_SIZE) != 0) {
					/* If the entry does not fit in the
					   block, the remainder of the block
					   becomes an unused entry */
					de->inode = 0;
					de->rec_len = BLOCK_SIZE
						- (offset & (BLOCK_SIZE - 1));
					de->name_len = 0;
					offset += de->rec_len;
					dir->i_size += de->rec_len;
					dir->i_dirt = 1;
#if 0
					dir->i_ctime = CURRENT_TIME;
#endif
					bh->b_dirt = 1;
				}
				brelse (bh);
				bh = NULL;
#ifdef EXTFS_DEBUG
printk ("ext_add_entry : creating next block\n");
#endif
				bh = ext_bread(dir,offset>>BLOCK_SIZE_BITS,1);
				if (!bh)
					return NULL; /* Other thing to do ??? */
				de = (struct ext_dir_entry *) bh->b_data;
			}
			/* Allocate the entry */
			de->inode=0;
			de->rec_len = rec_len;
			dir->i_size += de->rec_len;
			dir->i_dirt = 1;
#if 0
			dir->i_ctime = CURRENT_TIME;
#endif
		}
		if (de->rec_len < 8 || de->rec_len % 4 != 0 ||
		    de->rec_len < de->name_len + 8 ||
		    (((char *) de) + de->rec_len-1 >= BLOCK_SIZE+bh->b_data)) {
			printk ("ext_addr_entry: bad dir entry\n");
			printk ("dev=%d, dir=%d, offset=%d, rec_len=%d, name_len=%d\n",
				dir->i_dev, dir->i_ino, offset, de->rec_len, de->name_len);
			brelse (bh);
			return NULL;
		}
		if (!de->inode && de->rec_len >= rec_len) {
			if (de->rec_len > rec_len
			    && de->rec_len - rec_len >= EXT_DIR_MIN_SIZE) {
				/* The found entry is too big : it is split
				   into 2 ones :
				   - the 1st one will be used to hold the name,
				   - the 2nd one is unused */
				de1 = (struct ext_dir_entry *) ((char *) de + rec_len);
				de1->inode = 0;
				de1->rec_len = de->rec_len - rec_len;
				de1->name_len = 0;
				de->rec_len = rec_len;
			}
			dir->i_mtime = dir->i_ctime = CURRENT_TIME;
			de->name_len = namelen;
			for (i=0; i < namelen ; i++)
				de->name[i] = name[i];
			bh->b_dirt = 1;
			*res_dir = de;
			return bh;
		}
		offset += de->rec_len;
		de = (struct ext_dir_entry *) ((char *) de + de->rec_len);
	}
	brelse(bh);
	return NULL;
}

int ext_create(struct inode * dir,const char * name, int len, int mode,
	struct inode ** result)
{
	struct inode * inode;
	struct buffer_head * bh;
	struct ext_dir_entry * de;

	*result = NULL;
	if (!dir)
		return -ENOENT;
	inode = ext_new_inode(dir);
	if (!inode) {
		iput(dir);
		return -ENOSPC;
	}
	inode->i_op = &ext_file_inode_operations;
	inode->i_mode = mode;
	inode->i_dirt = 1;
	bh = ext_add_entry(dir,name,len,&de);
	if (!bh) {
		inode->i_nlink--;
		inode->i_dirt = 1;
		iput(inode);
		iput(dir);
		return -ENOSPC;
	}
	de->inode = inode->i_ino;
	bh->b_dirt = 1;
	brelse(bh);
	iput(dir);
	*result = inode;
	return 0;
}

int ext_mknod(struct inode * dir, const char * name, int len, int mode, int rdev)
{
	struct inode * inode;
	struct buffer_head * bh;
	struct ext_dir_entry * de;

	if (!dir)
		return -ENOENT;
	bh = ext_find_entry(dir,name,len,&de,NULL,NULL);
	if (bh) {
		brelse(bh);
		iput(dir);
		return -EEXIST;
	}
	inode = ext_new_inode(dir);
	if (!inode) {
		iput(dir);
		return -ENOSPC;
	}
	inode->i_uid = current->euid;
	inode->i_mode = mode;
	inode->i_op = NULL;
	if (S_ISREG(inode->i_mode))
		inode->i_op = &ext_file_inode_operations;
	else if (S_ISDIR(inode->i_mode)) {
		inode->i_op = &ext_dir_inode_operations;
		if (dir->i_mode & S_ISGID)
			inode->i_mode |= S_ISGID;
	}
	else if (S_ISLNK(inode->i_mode))
		inode->i_op = &ext_symlink_inode_operations;
	else if (S_ISCHR(inode->i_mode))
		inode->i_op = &chrdev_inode_operations;
	else if (S_ISBLK(inode->i_mode))
		inode->i_op = &blkdev_inode_operations;
	else if (S_ISFIFO(inode->i_mode))
		init_fifo(inode);
	if (S_ISBLK(mode) || S_ISCHR(mode))
		inode->i_rdev = rdev;
#if 0
	inode->i_mtime = inode->i_atime = CURRENT_TIME;
#endif
	inode->i_dirt = 1;
	bh = ext_add_entry(dir,name,len,&de);
	if (!bh) {
		inode->i_nlink--;
		inode->i_dirt = 1;
		iput(inode);
		iput(dir);
		return -ENOSPC;
	}
	de->inode = inode->i_ino;
	bh->b_dirt = 1;
	brelse(bh);
	iput(dir);
	iput(inode);
	return 0;
}

int ext_mkdir(struct inode * dir, const char * name, int len, int mode)
{
	struct inode * inode;
	struct buffer_head * bh, *dir_block;
	struct ext_dir_entry * de;
	
	bh = ext_find_entry(dir,name,len,&de,NULL,NULL);
	if (bh) {
		brelse(bh);
		iput(dir);
		return -EEXIST;
	}
	inode = ext_new_inode(dir);
	if (!inode) {
		iput(dir);
		return -ENOSPC;
	}
	inode->i_op = &ext_dir_inode_operations;
	inode->i_size = 2 * 16; /* Each entry is coded on 16 bytes for "." and ".."
					- 4 bytes for the inode number,
					- 2 bytes for the record length
					- 2 bytes for the name length
					- 8 bytes for the name */
#if 0
	inode->i_mtime = inode->i_atime = CURRENT_TIME;
#endif
	dir_block = ext_bread(inode,0,1);
	if (!dir_block) {
		iput(dir);
		inode->i_nlink--;
		inode->i_dirt = 1;
		iput(inode);
		return -ENOSPC;
	}
	de = (struct ext_dir_entry *) dir_block->b_data;
	de->inode=inode->i_ino;
	de->rec_len=16;
	de->name_len=1;
	strcpy(de->name,".");
	de = (struct ext_dir_entry *) ((char *) de + de->rec_len);
	de->inode = dir->i_ino;
	de->rec_len=16;
	de->name_len=2;
	strcpy(de->name,"..");
	inode->i_nlink = 2;
	dir_block->b_dirt = 1;
	brelse(dir_block);
	inode->i_mode = S_IFDIR | (mode & 0777 & ~current->umask);
	if (dir->i_mode & S_ISGID)