namei.c

LINUX1.0内核源代码,学习LINUX编程的一定要看。

/*
 *  linux/fs/ext2/namei.c
 *
 *  Copyright (C) 1992, 1993, 1994  Remy Card ([e-mail])
 *                                  Laboratoire MASI - Institut Blaise Pascal
 *                                  Universite Pierre et Marie Curie (Paris VI)
 *
 *  from
 *
 *  linux/fs/minix/namei.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <asm/segment.h>

#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/ext2_fs.h>
#include <linux/fcntl.h>
#include <linux/sched.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/locks.h>

/*
 * comment out this line if you want names > EXT2_NAME_LEN chars to be
 * truncated. Else they will be disallowed.
 */
/* #define NO_TRUNCATE */

/*
 * define how far ahead to read directories while searching them.
 */
#define NAMEI_RA_CHUNKS  2
#define NAMEI_RA_BLOCKS  4
#define NAMEI_RA_SIZE        (NAMEI_RA_CHUNKS * NAMEI_RA_BLOCKS)
#define NAMEI_RA_INDEX(c,b)  (((c) * NAMEI_RA_BLOCKS) + (b))

/*
 * NOTE! unlike strncmp, ext2_match returns 1 for success, 0 for failure.
 */
static int ext2_match (int len, const char * const name,
		       struct ext2_dir_entry * de)
{
	unsigned char same;

	if (!de || !de->inode || len > EXT2_NAME_LEN)
		return 0;
	/*
	 * "" means "." ---> so paths like "/usr/lib//libc.a" work
	 */
	if (!len && de->name_len == 1 && (de->name[0] == '.') &&
	   (de->name[1] == '\0'))
		return 1;
	if (len != de->name_len)
		return 0;
	__asm__("cld\n\t"
		"repe ; cmpsb\n\t"
		"setz %0"
		:"=q" (same)
		:"S" ((long) name), "D" ((long) de->name), "c" (len)
		:"cx", "di", "si");
	return (int) same;
}

/*
 *	ext2_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.
 */
static struct buffer_head * ext2_find_entry (struct inode * dir,
					     const char * const name, int namelen,
					     struct ext2_dir_entry ** res_dir)
{
	struct super_block * sb;
	struct buffer_head * bh_use[NAMEI_RA_SIZE];
	struct buffer_head * bh_read[NAMEI_RA_SIZE];
	unsigned long offset;
	int block, toread, i, err;

	*res_dir = NULL;
	if (!dir)
		return NULL;
	sb = dir->i_sb;

#ifdef NO_TRUNCATE
	if (namelen > EXT2_NAME_LEN)
		return NULL;
#else
	if (namelen > EXT2_NAME_LEN)
		namelen = EXT2_NAME_LEN;
#endif

	memset (bh_use, 0, sizeof (bh_use));
	toread = 0;
	for (block = 0; block < NAMEI_RA_SIZE; ++block) {
		struct buffer_head * bh;

		if ((block << EXT2_BLOCK_SIZE_BITS (sb)) >= dir->i_size)
			break;
		bh = ext2_getblk (dir, block, 0, &err);
		bh_use[block] = bh;
		if (bh && !bh->b_uptodate)
			bh_read[toread++] = bh;
	}

	block = 0;
	offset = 0;
	while (offset < dir->i_size) {
		struct buffer_head * bh;
		struct ext2_dir_entry * de;
		char * dlimit;

		if ((block % NAMEI_RA_BLOCKS) == 0 && toread) {
			ll_rw_block (READ, toread, bh_read);
			toread = 0;
		}
		bh = bh_use[block % NAMEI_RA_SIZE];
		if (!bh)
			ext2_panic (sb, "ext2_find_entry",
				    "buffer head pointer is NULL");
		wait_on_buffer (bh);
		if (!bh->b_uptodate) {
			/*
			 * read error: all bets are off
			 */
			break;
		}

		de = (struct ext2_dir_entry *) bh->b_data;
		dlimit = bh->b_data + sb->s_blocksize;
		while ((char *) de < dlimit) {
			if (!ext2_check_dir_entry ("ext2_find_entry", dir,
						   de, bh, offset))
				goto failure;
			if (de->inode != 0 && ext2_match (namelen, name, de)) {
				for (i = 0; i < NAMEI_RA_SIZE; ++i) {
					if (bh_use[i] != bh)
						brelse (bh_use[i]);
				}
				*res_dir = de;
				return bh;
			}
			offset += de->rec_len;
			de = (struct ext2_dir_entry *)
				((char *) de + de->rec_len);
		}

		brelse (bh);
		if (((block + NAMEI_RA_SIZE) << EXT2_BLOCK_SIZE_BITS (sb)) >=
		    dir->i_size)
			bh = NULL;
		else
			bh = ext2_getblk (dir, block + NAMEI_RA_SIZE, 0, &err);
		bh_use[block++ % NAMEI_RA_SIZE] = bh;
		if (bh && !bh->b_uptodate)
			bh_read[toread++] = bh;
	}

failure:
	for (i = 0; i < NAMEI_RA_SIZE; ++i)
		brelse (bh_use[i]);
	return NULL;
}

int ext2_lookup (struct inode * dir, const char * name, int len,
		 struct inode ** result)
{
	unsigned long ino;
	struct ext2_dir_entry * de;
	struct buffer_head * bh;

	*result = NULL;
	if (!dir)
		return -ENOENT;
	if (!S_ISDIR(dir->i_mode)) {
		iput (dir);
		return -ENOENT;
	}
#ifndef DONT_USE_DCACHE
	if (!(ino = ext2_dcache_lookup (dir->i_dev, dir->i_ino, name, len))) {
#endif
		if (!(bh = ext2_find_entry (dir, name, len, &de))) {
			iput (dir);
			return -ENOENT;
		}
		ino = de->inode;
#ifndef DONT_USE_DCACHE
		ext2_dcache_add (dir->i_dev, dir->i_ino, de->name,
				 de->name_len, ino);
#endif
		brelse (bh);
#ifndef DONT_USE_DCACHE
	}
#endif
	if (!(*result = iget (dir->i_sb, ino))) {
		iput (dir);
		return -EACCES;
	}
	iput (dir);
	return 0;
}

/*
 *	ext2_add_entry()
 *
 * adds a file entry to the specified directory, using the same
 * semantics as ext2_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 * ext2_add_entry (struct inode * dir,
					    const char * name, int namelen,
					    struct ext2_dir_entry ** res_dir,
					    int *err)
{
	unsigned long offset;
	unsigned short rec_len;
	struct buffer_head * bh;
	struct ext2_dir_entry * de, * de1;
	struct super_block * sb;

	*err = -EINVAL;
	*res_dir = NULL;
	if (!dir)
		return NULL;
	sb = dir->i_sb;
#ifdef NO_TRUNCATE
	if (namelen > EXT2_NAME_LEN)
		return NULL;
#else
	if (namelen > EXT2_NAME_LEN)
		namelen = EXT2_NAME_LEN;
#endif
	if (!namelen)
		return NULL;
	/*
	 * Is this a busy deleted directory?  Can't create new files if so
	 */
	if (dir->i_size == 0)
	{
		*err = -ENOENT;
		return NULL;
	}
	bh = ext2_bread (dir, 0, 0, err);
	if (!bh)
		return NULL;
	rec_len = EXT2_DIR_REC_LEN(namelen);
	offset = 0;
	de = (struct ext2_dir_entry *) bh->b_data;
	*err = -ENOSPC;
	while (1) {
		if ((char *)de >= sb->s_blocksize + bh->b_data) {
			brelse (bh);
			bh = NULL;
			bh = ext2_bread (dir, offset >> EXT2_BLOCK_SIZE_BITS(sb), 1, err);
			if (!bh)
				return NULL;
			if (dir->i_size <= offset) {
				if (dir->i_size == 0) {
					*err = -ENOENT;
					return NULL;
				}

				ext2_debug ("creating next block\n");

				de = (struct ext2_dir_entry *) bh->b_data;
				de->inode = 0;
				de->rec_len = sb->s_blocksize;
				dir->i_size = offset + sb->s_blocksize;
				dir->i_dirt = 1;
#if 0 /* XXX don't update any times until successful completion of syscall */
				dir->i_ctime = CURRENT_TIME;
#endif
			} else {

				ext2_debug ("skipping to next block\n");

				de = (struct ext2_dir_entry *) bh->b_data;
			}
		}
		if (!ext2_check_dir_entry ("ext2_add_entry", dir, de, bh,
					   offset)) {
			*err = -ENOENT;
			brelse (bh);
			return NULL;
		}
		if (de->inode != 0 && ext2_match (namelen, name, de)) {
				*err = -EEXIST;
				brelse (bh);
				return NULL;
		}
		if ((de->inode == 0 && de->rec_len >= rec_len) ||
		    (de->rec_len >= EXT2_DIR_REC_LEN(de->name_len) + rec_len)) {
			offset += de->rec_len;
			if (de->inode) {
				de1 = (struct ext2_dir_entry *) ((char *) de +
					EXT2_DIR_REC_LEN(de->name_len));
				de1->rec_len = de->rec_len -
					EXT2_DIR_REC_LEN(de->name_len);
				de->rec_len = EXT2_DIR_REC_LEN(de->name_len);
				de = de1;
			}
			de->inode = 0;
			de->name_len = namelen;
			memcpy (de->name, name, namelen);
			/*
			 * XXX shouldn't update any times until successful
			 * completion of syscall, but too many callers depend
			 * on this.
			 *
			 * XXX similarly, too many callers depend on
			 * ext2_new_inode() setting the times, but error
			 * recovery deletes the inode, so the worst that can
			 * happen is that the times are slightly out of date
			 * and/or different from the directory change time.
			 */
			dir->i_mtime = dir->i_ctime = CURRENT_TIME;
			dir->i_dirt = 1;
			bh->b_dirt = 1;
			*res_dir = de;
			*err = 0;
			return bh;
		}
		offset += de->rec_len;
		de = (struct ext2_dir_entry *) ((char *) de + de->rec_len);
	}
	brelse (bh);
	return NULL;
}

/*
 * ext2_delete_entry deletes a directory entry by merging it with the
 * previous entry
 */
static int ext2_delete_entry (struct ext2_dir_entry * dir,
			      struct buffer_head * bh)
{
	struct ext2_dir_entry * de, * pde;
	int i;

	i = 0;
	pde = NULL;
	de = (struct ext2_dir_entry *) bh->b_data;
	while (i < bh->b_size) {
		if (!ext2_check_dir_entry ("ext2_delete_entry", NULL, 
					   de, bh, i))
			return -EIO;
		if (de == dir)  {
			if (pde)
				pde->rec_len += dir->rec_len;
			dir->inode = 0;
			return 0;
		}
		i += de->rec_len;
		pde = de;
		de = (struct ext2_dir_entry *) ((char *) de + de->rec_len);
	}
	return -ENOENT;
}

int ext2_create (struct inode * dir,const char * name, int len, int mode,
		 struct inode ** result)
{
	struct inode * inode;
	struct buffer_head * bh;
	struct ext2_dir_entry * de;
	int err;

	*result = NULL;
	if (!dir)
		return -ENOENT;
	inode = ext2_new_inode (dir, mode);
	if (!inode) {
		iput (dir);
		return -ENOSPC;
	}
	inode->i_op = &ext2_file_inode_operations;
	inode->i_mode = mode;
	inode->i_dirt = 1;
	bh = ext2_add_entry (dir, name, len, &de, &err);
	if (!bh) {
		inode->i_nlink--;
		inode->i_dirt = 1;
		iput (inode);
		iput (dir);
		return err;
	}
	de->inode = inode->i_ino;
#ifndef DONT_USE_DCACHE
	ext2_dcache_add (dir->i_dev, dir->i_ino, de->name, de->name_len,
			 de->inode);
#endif
	bh->b_dirt = 1;
	if (IS_SYNC(dir)) {
		ll_rw_block (WRITE, 1, &bh);
		wait_on_buffer (bh);
	}
	brelse (bh);
	iput (dir);
	*result = inode;
	return 0;
}

int ext2_mknod (struct inode * dir, const char * name, int len, int mode,
		int rdev)
{
	struct inode * inode;
	struct buffer_head * bh;
	struct ext2_dir_entry * de;
	int err;

	if (!dir)
		return -ENOENT;
	bh = ext2_find_entry (dir, name, len, &de);
	if (bh) {
		brelse (bh);
		iput (dir);
		return -EEXIST;
	}
	inode = ext2_new_inode (dir, mode);
	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 = &ext2_file_inode_operations;
	else if (S_ISDIR(inode->i_mode)) {
		inode->i_op = &ext2_dir_inode_operations;
		if (dir->i_mode & S_ISGID)
			inode->i_mode |= S_ISGID;
	}
	else if (S_ISLNK(inode->i_mode))
		inode->i_op = &ext2_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
	/*
	 * XXX we may as well use the times set by ext2_new_inode().  The
	 * following usually does nothing, but sometimes it invalidates
	 * inode->i_ctime.
	 */
	inode->i_mtime = inode->i_atime = CURRENT_TIME;
#endif
	inode->i_dirt = 1;
	bh = ext2_add_entry (dir, name, len, &de, &err);
	if (!bh) {
		inode->i_nlink--;
		inode->i_dirt = 1;
		iput (inode);
		iput (dir);
		return err;
	}
	de->inode = inode->i_ino;
#ifndef DONT_USE_DCACHE
	ext2_dcache_add (dir->i_dev, dir->i_ino, de->name, de->name_len,
			 de->inode);
#endif
	bh->b_dirt = 1;
	if (IS_SYNC(dir)) {
		ll_rw_block (WRITE, 1, &bh);
		wait_on_buffer (bh);
	}
	brelse (bh);
	iput (dir);
	iput (inode);
	return 0;
}

int ext2_mkdir (struct inode * dir, const char * name, int len, int mode)
{
	struct inode * inode;
	struct buffer_head * bh, * dir_block;
	struct ext2_dir_entry * de;
	int err;

	if (!dir)
		return -ENOENT;
	bh = ext2_find_entry (dir, name, len, &de);
	if (bh) {
		brelse (bh);
		iput (dir);
		return -EEXIST;
	}
	if (dir->i_nlink >= EXT2_LINK_MAX) {
		iput (dir);
		return -EMLINK;
	}
	inode = ext2_new_inode (dir, S_IFDIR);
	if (!inode) {
		iput (dir);
		return -ENOSPC;
	}
	inode->i_op = &ext2_dir_inode_operations;
	inode->i_size = inode->i_sb->s_blocksize;
#if 0 /* XXX as above */
	inode->i_mtime = inode->i_atime = CURRENT_TIME;
#endif
	dir_block = ext2_bread (inode, 0, 1, &err);
	if (!dir_block) {
		iput (dir);
		inode->i_nlink--;
		inode->i_dirt = 1;
		iput (inode);
		return err;
	}
	inode->i_blocks = inode->i_sb->s_blocksize / 512;
	de = (struct ext2_dir_entry *) dir_block->b_data;
	de->inode = inode->i_ino;
	de->name_len = 1;
	de->rec_len = EXT2_DIR_REC_LEN(de->name_len);
	strcpy (de->name, ".");
	de = (struct ext2_dir_entry *) ((char *) de + de->rec_len);
	de->inode = dir->i_ino;
	de->rec_len = inode->i_sb->s_blocksize - EXT2_DIR_REC_LEN(1);
	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 & S_IRWXUGO & ~current->umask);
	if (dir->i_mode & S_ISGID)
		inode->i_mode |= S_ISGID;
	inode->i_dirt = 1;
	bh = ext2_add_entry (dir, name, len, &de, &err);
	if (!bh) {
		iput (dir);
		inode->i_nlink = 0;
		inode->i_dirt = 1;
		iput (inode);
		return err;
	}
	de->inode = inode->i_ino;
#ifndef DONT_USE_DCACHE
	ext2_dcache_add (dir->i_dev, dir->i_ino, de->name, de->name_len,
			 de->inode);
#endif
	bh->b_dirt = 1;
	if (IS_SYNC(dir)) {
		ll_rw_block (WRITE, 1, &bh);
		wait_on_buffer (bh);
	}
	dir->i_nlink++;
	dir->i_dirt = 1;
	iput (dir);
	iput (inode);