namei.c

LINUX1.0内核源代码,学习LINUX编程的一定要看。

		inode->i_mode |= S_ISGID;
	inode->i_dirt = 1;
	bh = ext_add_entry(dir,name,len,&de);
	if (!bh) {
		iput(dir);
		inode->i_nlink=0;
		iput(inode);
		return -ENOSPC;
	}
	de->inode = inode->i_ino;
	bh->b_dirt = 1;
	dir->i_nlink++;
	dir->i_dirt = 1;
	iput(dir);
	iput(inode);
	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 ext_dir_entry * de, * de1;

	if (inode->i_size < 2 * 12 || !(bh = ext_bread(inode,0,0))) {
	    	printk("warning - bad directory on dev %04x\n",inode->i_dev);
		return 1;
	}
	de = (struct ext_dir_entry *) bh->b_data;
	de1 = (struct ext_dir_entry *) ((char *) de + de->rec_len);
	if (de->inode != inode->i_ino || !de1->inode || 
	    strcmp(".",de->name) || strcmp("..",de1->name)) {
	    	printk("warning - bad directory on dev %04x\n",inode->i_dev);
		return 1;
	}
	offset = de->rec_len + de1->rec_len;
	de = (struct ext_dir_entry *) ((char *) de1 + de1->rec_len);
	while (offset < inode->i_size ) {
		if ((void *) de >= (void *) (bh->b_data+BLOCK_SIZE)) {
			brelse(bh);
			bh = ext_bread(inode, offset >> BLOCK_SIZE_BITS,1);
			if (!bh) {
				offset += BLOCK_SIZE;
				continue;
			}
			de = (struct ext_dir_entry *) bh->b_data;
		}
		if (de->rec_len < 8 || de->rec_len %4 != 0 ||
		    de->rec_len < de->name_len + 8) {
			printk ("empty_dir: bad dir entry\n");
			printk ("dev=%d, dir=%d, offset=%d, rec_len=%d, name_len=%d\n",
				inode->i_dev, inode->i_ino, offset, de->rec_len, de->name_len);
			brelse (bh);
			return 1;
		}
		if (de->inode) {
			brelse(bh);
			return 0;
		}
		offset += de->rec_len;
		de = (struct ext_dir_entry *) ((char *) de + de->rec_len);
	}
	brelse(bh);
	return 1;
}

static inline void ext_merge_entries (struct ext_dir_entry * de,
	struct ext_dir_entry * pde, struct ext_dir_entry * nde)
{
	if (nde && !nde->inode)
		de->rec_len += nde->rec_len;
	if (pde && !pde->inode)
		pde->rec_len += de->rec_len;
}

int ext_rmdir(struct inode * dir, const char * name, int len)
{
	int retval;
	struct inode * inode;
	struct buffer_head * bh;
	struct ext_dir_entry * de, * pde, * nde;

	inode = NULL;
	bh = ext_find_entry(dir,name,len,&de,&pde,&nde);
	retval = -ENOENT;
	if (!bh)
		goto end_rmdir;
	retval = -EPERM;
	if (!(inode = iget(dir->i_sb, de->inode)))
		goto end_rmdir;
	if ((dir->i_mode & S_ISVTX) && current->euid &&
	   inode->i_uid != current->euid)
		goto end_rmdir;
	if (inode->i_dev != dir->i_dev)
		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;
	}
	if (!empty_dir(inode)) {
		retval = -ENOTEMPTY;
		goto end_rmdir;
	}
	if (inode->i_count > 1) {
		retval = -EBUSY;
		goto end_rmdir;
	}
	if (inode->i_nlink != 2)
		printk("empty directory has nlink!=2 (%d)\n",inode->i_nlink);
	de->inode = 0;
	de->name_len = 0;
	ext_merge_entries (de, pde, nde);
	bh->b_dirt = 1;
	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;
	retval = 0;
end_rmdir:
	iput(dir);
	iput(inode);
	brelse(bh);
	return retval;
}

int ext_unlink(struct inode * dir, const char * name, int len)
{
	int retval;
	struct inode * inode;
	struct buffer_head * bh;
	struct ext_dir_entry * de, * pde, * nde;

	retval = -ENOENT;
	inode = NULL;
	bh = ext_find_entry(dir,name,len,&de,&pde,&nde);
	if (!bh)
		goto end_unlink;
	if (!(inode = iget(dir->i_sb, de->inode)))
		goto end_unlink;
	retval = -EPERM;
	if ((dir->i_mode & S_ISVTX) && !suser() &&
	    current->euid != inode->i_uid &&
	    current->euid != dir->i_uid)
		goto end_unlink;
	if (S_ISDIR(inode->i_mode))
		goto end_unlink;
	if (!inode->i_nlink) {
		printk("Deleting nonexistent file (%04x:%d), %d\n",
			inode->i_dev,inode->i_ino,inode->i_nlink);
		inode->i_nlink=1;
	}
	de->inode = 0;
	de->name_len = 0;
	ext_merge_entries (de, pde, nde);
	bh->b_dirt = 1;
	inode->i_nlink--;
	inode->i_dirt = 1;
	inode->i_ctime = CURRENT_TIME;
	dir->i_ctime = dir->i_mtime = inode->i_ctime;
	dir->i_dirt = 1;
	retval = 0;
end_unlink:
	brelse(bh);
	iput(inode);
	iput(dir);
	return retval;
}

int ext_symlink(struct inode * dir, const char * name, int len, const char * symname)
{
	struct ext_dir_entry * de;
	struct inode * inode = NULL;
	struct buffer_head * bh = NULL, * name_block = NULL;
	int i;
	char c;

	if (!(inode = ext_new_inode(dir))) {
		iput(dir);
		return -ENOSPC;
	}
	inode->i_mode = S_IFLNK | 0777;
	inode->i_op = &ext_symlink_inode_operations;
	name_block = ext_bread(inode,0,1);
	if (!name_block) {
		iput(dir);
		inode->i_nlink--;
		inode->i_dirt = 1;
		iput(inode);
		return -ENOSPC;
	}
	i = 0;
	while (i < 1023 && (c = *(symname++)))
		name_block->b_data[i++] = c;
	name_block->b_data[i] = 0;
	name_block->b_dirt = 1;
	brelse(name_block);
	inode->i_size = i;
	inode->i_dirt = 1;
	bh = ext_find_entry(dir,name,len,&de,NULL,NULL);
	if (bh) {
		inode->i_nlink--;
		inode->i_dirt = 1;
		iput(inode);
		brelse(bh);
		iput(dir);
		return -EEXIST;
	}
	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_link(struct inode * oldinode, struct inode * dir, const char * name, int len)
{
	struct ext_dir_entry * de;
	struct buffer_head * bh;

	if (S_ISDIR(oldinode->i_mode)) {
		iput(oldinode);
		iput(dir);
		return -EPERM;
	}
	if (oldinode->i_nlink > 32000) {
		iput(oldinode);
		iput(dir);
		return -EMLINK;
	}
	bh = ext_find_entry(dir,name,len,&de,NULL,NULL);
	if (bh) {
		brelse(bh);
		iput(dir);
		iput(oldinode);
		return -EEXIST;
	}
	bh = ext_add_entry(dir,name,len,&de);
	if (!bh) {
		iput(dir);
		iput(oldinode);
		return -ENOSPC;
	}
	de->inode = oldinode->i_ino;
	bh->b_dirt = 1;
	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 (ext_lookup(new_inode,"..",2,&new_inode))
			break;
		if (new_inode->i_ino == ino)
			break;
	}
	iput(new_inode);
	return result;
}

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

#define PARENT_NAME(buffer) \
((struct ext_dir_entry *) ((char *) buffer + \
((struct ext_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_ext_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 ext_dir_entry * old_de, * new_de, * pde, * nde;
	int retval;

	goto start_up;
try_again:
	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;
	old_bh = ext_find_entry(old_dir,old_name,old_len,&old_de,&pde,&nde);
	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 = ext_find_entry(new_dir,new_name,new_len,&new_de,NULL,NULL);
	if (new_bh) {
		new_inode = __iget(new_dir->i_sb, new_de->inode,0); /* don't cross mnt-points */
		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 = -EEXIST;
		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 = -EEXIST;
		if (new_bh)
			goto end_rename;
		retval = -EACCES;
		if (!permission(old_inode, MAY_WRITE))
			goto end_rename;
		retval = -EINVAL;
		if (subdir(new_dir, old_inode))
			goto end_rename;
		retval = -EIO;
		dir_bh = ext_bread(old_inode,0,0);
		if (!dir_bh)
			goto end_rename;
		if (PARENT_INO(dir_bh->b_data) != old_dir->i_ino)
			goto end_rename;
	}
	if (!new_bh)
		new_bh = ext_add_entry(new_dir,new_name,new_len,&new_de);
	retval = -ENOSPC;
	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 */
	old_de->inode = 0;
	old_de->name_len = 0;
	new_de->inode = old_inode->i_ino;
	ext_merge_entries (old_de, pde, nde);
	if (new_inode) {
		new_inode->i_nlink--;
		new_inode->i_dirt = 1;
	}
	old_bh->b_dirt = 1;
	new_bh->b_dirt = 1;
	if (dir_bh) {
		PARENT_INO(dir_bh->b_data) = new_dir->i_ino;
		dir_bh->b_dirt = 1;
		old_dir->i_nlink--;
		new_dir->i_nlink++;
		old_dir->i_dirt = 1;
		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.
 */
int ext_rename(struct inode * old_dir, const char * old_name, int old_len,
	struct inode * new_dir, const char * new_name, int new_len)
{
	static struct wait_queue * wait = NULL;
	static int lock = 0;
	int result;

	while (lock)
		sleep_on(&wait);
	lock = 1;
	result = do_ext_rename(old_dir, old_name, old_len,
		new_dir, new_name, new_len);
	lock = 0;
	wake_up(&wait);
	return result;
}