namei.c

LINUX1.0内核源代码,学习LINUX编程的一定要看。

	brelse (bh);
	return 0;
}

/*
 * routine to check that the specified directory is empty (for rmdir)
 */
static int empty_dir (struct inode * inode)
{
	unsigned long offset;
	struct buffer_head * bh;
	struct ext2_dir_entry * de, * de1;
	struct super_block * sb;
	int err;

	sb = inode->i_sb;
	if (inode->i_size < EXT2_DIR_REC_LEN(1) + EXT2_DIR_REC_LEN(2) ||
	    !(bh = ext2_bread (inode, 0, 0, &err))) {
	    	ext2_warning (inode->i_sb, "empty_dir",
			      "bad directory (dir %lu)", inode->i_ino);
		return 1;
	}
	de = (struct ext2_dir_entry *) bh->b_data;
	de1 = (struct ext2_dir_entry *) ((char *) de + de->rec_len);
	if (de->inode != inode->i_ino || !de1->inode || 
	    strcmp (".", de->name) || strcmp ("..", de1->name)) {
	    	ext2_warning (inode->i_sb, "empty_dir",
			      "bad directory (dir %lu)", inode->i_ino);
		return 1;
	}
	offset = de->rec_len + de1->rec_len;
	de = (struct ext2_dir_entry *) ((char *) de1 + de1->rec_len);
	while (offset < inode->i_size ) {
		if ((void *) de >= (void *) (bh->b_data + sb->s_blocksize)) {
			brelse (bh);
			bh = ext2_bread (inode, offset >> EXT2_BLOCK_SIZE_BITS(sb), 1, &err);
			if (!bh) {
				offset += sb->s_blocksize;
				continue;
			}
			de = (struct ext2_dir_entry *) bh->b_data;
		}
		if (!ext2_check_dir_entry ("empty_dir", inode, de, bh,
					   offset)) {
			brelse (bh);
			return 1;
		}
		if (de->inode) {
			brelse (bh);
			return 0;
		}
		offset += de->rec_len;
		de = (struct ext2_dir_entry *) ((char *) de + de->rec_len);
	}
	brelse (bh);
	return 1;
}

int ext2_rmdir (struct inode * dir, const char * name, int len)
{
	int retval;
	struct inode * inode;
	struct buffer_head * bh;
	struct ext2_dir_entry * de;

repeat:
	if (!dir)
		return -ENOENT;
	inode = NULL;
	bh = ext2_find_entry (dir, name, len, &de);
	retval = -ENOENT;
	if (!bh)
		goto end_rmdir;
	retval = -EPERM;
	if (!(inode = iget (dir->i_sb, de->inode)))
		goto end_rmdir;
	if (inode->i_dev != dir->i_dev)
		goto end_rmdir;
	if (de->inode != inode->i_ino) {
		iput(inode);
		brelse(bh);
		current->counter = 0;
		schedule();
		goto repeat;
	}
	if ((dir->i_mode & S_ISVTX) && current->euid &&
	    inode->i_uid != current->euid)
		goto end_rmdir;
	if (inode == dir)	/* we may not delete ".", but "../dir" is ok */
		goto end_rmdir;
	if (!S_ISDIR(inode->i_mode)) {
		retval = -ENOTDIR;
		goto end_rmdir;
	}
	down(&inode->i_sem);
	if (!empty_dir (inode))
		retval = -ENOTEMPTY;
	else if (de->inode != inode->i_ino)
		retval = -ENOENT;
	else {
		if (inode->i_count > 1) {
		/*
		 * Are we deleting the last instance of a busy directory?
		 * Better clean up if so.
		 *
		 * Make directory empty (it will be truncated when finally
		 * dereferenced).  This also inhibits ext2_add_entry.
		 */
			inode->i_size = 0;
		}
		retval = ext2_delete_entry (de, bh);
	}
	up(&inode->i_sem);
	if (retval)
		goto end_rmdir;
	bh->b_dirt = 1;
	if (IS_SYNC(dir)) {
		ll_rw_block (WRITE, 1, &bh);
		wait_on_buffer (bh);
	}
#ifndef DONT_USE_DCACHE
	ext2_dcache_remove(inode->i_dev, inode->i_ino, ".", 1);
	ext2_dcache_remove(inode->i_dev, inode->i_ino, "..", 2);
#endif
	if (inode->i_nlink != 2)
		ext2_warning (inode->i_sb, "ext2_rmdir",
			      "empty directory has nlink!=2 (%d)",
			      inode->i_nlink);
#ifndef DONT_USE_DCACHE
	ext2_dcache_remove (dir->i_dev, dir->i_ino, de->name, de->name_len);
#endif
	inode->i_nlink = 0;
	inode->i_dirt = 1;
	dir->i_nlink--;
	inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
	dir->i_dirt = 1;
end_rmdir:
	iput (dir);
	iput (inode);
	brelse (bh);
	return retval;
}

int ext2_unlink (struct inode * dir, const char * name, int len)
{
	int retval;
	struct inode * inode;
	struct buffer_head * bh;
	struct ext2_dir_entry * de;

repeat:
	if (!dir)
		return -ENOENT;
	retval = -ENOENT;
	inode = NULL;
	bh = ext2_find_entry (dir, name, len, &de);
	if (!bh)
		goto end_unlink;
	if (!(inode = iget (dir->i_sb, de->inode)))
		goto end_unlink;
	retval = -EPERM;
	if (S_ISDIR(inode->i_mode))
		goto end_unlink;
	if (de->inode != inode->i_ino) {
		iput(inode);
		brelse(bh);
		current->counter = 0;
		schedule();
		goto repeat;
	}
	if ((dir->i_mode & S_ISVTX) && !suser() &&
	    current->euid != inode->i_uid &&
	    current->euid != dir->i_uid)
		goto end_unlink;
	if (!inode->i_nlink) {
		ext2_warning (inode->i_sb, "ext2_unlink",
			      "Deleting nonexistent file (%lu), %d",
			      inode->i_ino, inode->i_nlink);
		inode->i_nlink = 1;
	}
	retval = ext2_delete_entry (de, bh);
	if (retval)
		goto end_unlink;
	bh->b_dirt = 1;
	if (IS_SYNC(dir)) {
		ll_rw_block (WRITE, 1, &bh);
		wait_on_buffer (bh);
	}
#ifndef DONT_USE_DCACHE
	ext2_dcache_remove (dir->i_dev, dir->i_ino, de->name, de->name_len);
#endif
	dir->i_ctime = dir->i_mtime = CURRENT_TIME;
	dir->i_dirt = 1;
	inode->i_nlink--;
	inode->i_dirt = 1;
	inode->i_ctime = dir->i_ctime;
	retval = 0;
end_unlink:
	brelse (bh);
	iput (inode);
	iput (dir);
	return retval;
}

int ext2_symlink (struct inode * dir, const char * name, int len,
		  const char * symname)
{
	struct ext2_dir_entry * de;
	struct inode * inode = NULL;
	struct buffer_head * bh = NULL, * name_block = NULL;
	char * link;
	int i, err;
	int l;
	char c;

	if (!(inode = ext2_new_inode (dir, S_IFLNK))) {
		iput (dir);
		return -ENOSPC;
	}
	inode->i_mode = S_IFLNK | S_IRWXUGO;
	inode->i_op = &ext2_symlink_inode_operations;
	for (l = 0; l < inode->i_sb->s_blocksize - 1 &&
	     symname [l]; l++)
		;
	if (l >= EXT2_N_BLOCKS * sizeof (unsigned long)) {

		ext2_debug ("l=%d, normal symlink\n", l);

		name_block = ext2_bread (inode, 0, 1, &err);
		if (!name_block) {
			iput (dir);
			inode->i_nlink--;
			inode->i_dirt = 1;
			iput (inode);
			return err;
		}
		link = name_block->b_data;
	} else {
		link = (char *) inode->u.ext2_i.i_data;

		ext2_debug ("l=%d, fast symlink\n", l);

	}
	i = 0;
	while (i < inode->i_sb->s_blocksize - 1 && (c = *(symname++)))
		link[i++] = c;
	link[i] = 0;
	if (name_block) {
		name_block->b_dirt = 1;
		brelse (name_block);
	}
	inode->i_size = i;
	inode->i_dirt = 1;
	bh = ext2_find_entry (dir, name, len, &de);
	if (bh) {
		inode->i_nlink--;
		inode->i_dirt = 1;
		iput (inode);
		brelse (bh);
		iput (dir);
		return -EEXIST;
	}
	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_link (struct inode * oldinode, struct inode * dir,
	       const char * name, int len)
{
	struct ext2_dir_entry * de;
	struct buffer_head * bh;
	int err;

	if (S_ISDIR(oldinode->i_mode)) {
		iput (oldinode);
		iput (dir);
		return -EPERM;
	}
	if (oldinode->i_nlink >= EXT2_LINK_MAX) {
		iput (oldinode);
		iput (dir);
		return -EMLINK;
	}
	bh = ext2_find_entry (dir, name, len, &de);
	if (bh) {
		brelse (bh);
		iput (dir);
		iput (oldinode);
		return -EEXIST;
	}
	bh = ext2_add_entry (dir, name, len, &de, &err);
	if (!bh) {
		iput (dir);
		iput (oldinode);
		return err;
	}
	de->inode = oldinode->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);
	oldinode->i_nlink++;
	oldinode->i_ctime = CURRENT_TIME;
	oldinode->i_dirt = 1;
	iput (oldinode);
	return 0;
}

static int subdir (struct inode * new_inode, struct inode * old_inode)
{
	int ino;
	int result;

	new_inode->i_count++;
	result = 0;
	for (;;) {
		if (new_inode == old_inode) {
			result = 1;
			break;
		}
		if (new_inode->i_dev != old_inode->i_dev)
			break;
		ino = new_inode->i_ino;
		if (ext2_lookup (new_inode, "..", 2, &new_inode))
			break;
		if (new_inode->i_ino == ino)
			break;
	}
	iput (new_inode);
	return result;
}

#define PARENT_INO(buffer) \
	((struct ext2_dir_entry *) ((char *) buffer + \
	((struct ext2_dir_entry *) buffer)->rec_len))->inode

#define PARENT_NAME(buffer) \
	((struct ext2_dir_entry *) ((char *) buffer + \
	((struct ext2_dir_entry *) buffer)->rec_len))->name

/*
 * rename uses retrying to avoid race-conditions: at least they should be
 * minimal.
 * it tries to allocate all the blocks, then sanity-checks, and if the sanity-
 * checks fail, it tries to restart itself again. Very practical - no changes
 * are done until we know everything works ok.. and then all the changes can be
 * done in one fell swoop when we have claimed all the buffers needed.
 *
 * Anybody can rename anything with this: the permission checks are left to the
 * higher-level routines.
 */
static int do_ext2_rename (struct inode * old_dir, const char * old_name,
			   int old_len, struct inode * new_dir,
			   const char * new_name, int new_len)
{
	struct inode * old_inode, * new_inode;
	struct buffer_head * old_bh, * new_bh, * dir_bh;
	struct ext2_dir_entry * old_de, * new_de;
	int retval;

	goto start_up;
try_again:
	if (new_bh && new_de)
		ext2_delete_entry(new_de, new_bh);
	brelse (old_bh);
	brelse (new_bh);
	brelse (dir_bh);
	iput (old_inode);
	iput (new_inode);
	current->counter = 0;
	schedule ();
start_up:
	old_inode = new_inode = NULL;
	old_bh = new_bh = dir_bh = NULL;
	new_de = NULL;
	old_bh = ext2_find_entry (old_dir, old_name, old_len, &old_de);
	retval = -ENOENT;
	if (!old_bh)
		goto end_rename;
	old_inode = __iget (old_dir->i_sb, old_de->inode, 0); /* don't cross mnt-points */
	if (!old_inode)
		goto end_rename;
	retval = -EPERM;
	if ((old_dir->i_mode & S_ISVTX) && 
	    current->euid != old_inode->i_uid &&
	    current->euid != old_dir->i_uid && !suser())
		goto end_rename;
	new_bh = ext2_find_entry (new_dir, new_name, new_len, &new_de);
	if (new_bh) {
		new_inode = __iget (new_dir->i_sb, new_de->inode, 0); /* no mntp cross */
		if (!new_inode) {
			brelse (new_bh);
			new_bh = NULL;
		}
	}
	if (new_inode == old_inode) {
		retval = 0;
		goto end_rename;
	}
	if (new_inode && S_ISDIR(new_inode->i_mode)) {
		retval = -EISDIR;
		if (!S_ISDIR(old_inode->i_mode))
			goto end_rename;
		retval = -EINVAL;
		if (subdir (new_dir, old_inode))
			goto end_rename;
		retval = -ENOTEMPTY;
		if (!empty_dir (new_inode))
			goto end_rename;
		retval = -EBUSY;
		if (new_inode->i_count > 1)
			goto end_rename;
	}
	retval = -EPERM;
	if (new_inode && (new_dir->i_mode & S_ISVTX) &&
	    current->euid != new_inode->i_uid &&
	    current->euid != new_dir->i_uid && !suser())
		goto end_rename;
	if (S_ISDIR(old_inode->i_mode)) {
		retval = -ENOTDIR;
		if (new_inode && !S_ISDIR(new_inode->i_mode))
			goto end_rename;
		retval = -EINVAL;
		if (subdir (new_dir, old_inode))
			goto end_rename;
		dir_bh = ext2_bread (old_inode, 0, 0, &retval);
		if (!dir_bh)
			goto end_rename;
		if (PARENT_INO(dir_bh->b_data) != old_dir->i_ino)
			goto end_rename;
		retval = -EMLINK;
		if (!new_inode && new_dir->i_nlink >= EXT2_LINK_MAX)
			goto end_rename;
	}
	if (!new_bh)
		new_bh = ext2_add_entry (new_dir, new_name, new_len, &new_de,
					 &retval);
	if (!new_bh)
		goto end_rename;
	/*
	 * sanity checking before doing the rename - avoid races
	 */
	if (new_inode && (new_de->inode != new_inode->i_ino))
		goto try_again;
	if (new_de->inode && !new_inode)
		goto try_again;
	if (old_de->inode != old_inode->i_ino)
		goto try_again;
	/*
	 * ok, that's it
	 */
	new_de->inode = old_inode->i_ino;
#ifndef DONT_USE_DCACHE
	ext2_dcache_remove (old_dir->i_dev, old_dir->i_ino, old_de->name,
			    old_de->name_len);
	ext2_dcache_add (new_dir->i_dev, new_dir->i_ino, new_de->name,
			 new_de->name_len, new_de->inode);
#endif
	retval = ext2_delete_entry (old_de, old_bh);
	if (retval == -ENOENT)
		goto try_again;
	if (retval)
		goto end_rename;
	if (new_inode) {
		new_inode->i_nlink--;
		new_inode->i_ctime = CURRENT_TIME;
		new_inode->i_dirt = 1;
	}
	old_dir->i_ctime = old_dir->i_mtime = CURRENT_TIME;
	old_dir->i_dirt = 1;
	old_bh->b_dirt = 1;
	if (IS_SYNC(old_dir)) {
		ll_rw_block (WRITE, 1, &old_bh);
		wait_on_buffer (old_bh);
	}
	new_bh->b_dirt = 1;
	if (IS_SYNC(new_dir)) {
		ll_rw_block (WRITE, 1, &new_bh);
		wait_on_buffer (new_bh);
	}
	if (dir_bh) {
		PARENT_INO(dir_bh->b_data) = new_dir->i_ino;
		dir_bh->b_dirt = 1;
		old_dir->i_nlink--;
		old_dir->i_dirt = 1;
		if (new_inode) {
			new_inode->i_nlink--;
			new_inode->i_dirt = 1;
		} else {
			new_dir->i_nlink++;
			new_dir->i_dirt = 1;
		}
	}
	retval = 0;
end_rename:
	brelse (dir_bh);
	brelse (old_bh);
	brelse (new_bh);
	iput (old_inode);
	iput (new_inode);
	iput (old_dir);
	iput (new_dir);
	return retval;
}

/*
 * Ok, rename also locks out other renames, as they can change the parent of
 * a directory, and we don't want any races. Other races are checked for by
 * "do_rename()", which restarts if there are inconsistencies.
 *
 * Note that there is no race between different filesystems: it's only within
 * the same device that races occur: many renames can happen at once, as long
 * as they are on different partitions.
 *
 * In the second extended file system, we use a lock flag stored in the memory
 * super-block.  This way, we really lock other renames only if they occur
 * on the same file system
 */
int ext2_rename (struct inode * old_dir, const char * old_name, int old_len,
		 struct inode * new_dir, const char * new_name, int new_len)
{
	int result;

	while (old_dir->i_sb->u.ext2_sb.s_rename_lock)
		sleep_on (&old_dir->i_sb->u.ext2_sb.s_rename_wait);
	old_dir->i_sb->u.ext2_sb.s_rename_lock = 1;
	result = do_ext2_rename (old_dir, old_name, old_len, new_dir,
				 new_name, new_len);
	old_dir->i_sb->u.ext2_sb.s_rename_lock = 0;
	wake_up (&old_dir->i_sb->u.ext2_sb.s_rename_wait);
	return result;
}