erofs: get rid of erofs_prepare_dio() helper

Fold in erofs_prepare_dio() in order to simplify the code.
Reviewed-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220720082229.12172-1-hsiangkao@linux.alibaba.com

fs/erofs/data.c

@@ -366,42 +366,33 @@ static sector_t erofs_bmap(struct address_space *mapping, sector_t block)
 	return iomap_bmap(mapping, block, &erofs_iomap_ops);
 }
 
-static int erofs_prepare_dio(struct kiocb *iocb, struct iov_iter *to)
+static ssize_t erofs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
-	loff_t align = iocb->ki_pos | iov_iter_count(to) |
-		iov_iter_alignment(to);
-	struct block_device *bdev = inode->i_sb->s_bdev;
-	unsigned int blksize_mask;
-
-	if (bdev)
-		blksize_mask = (1 << ilog2(bdev_logical_block_size(bdev))) - 1;
-	else
-		blksize_mask = (1 << inode->i_blkbits) - 1;
 
-	if (align & blksize_mask)
-		return -EINVAL;
-	return 0;
-}
-
-static ssize_t erofs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
-{
 	/* no need taking (shared) inode lock since it's a ro filesystem */
 	if (!iov_iter_count(to))
 		return 0;
 
 #ifdef CONFIG_FS_DAX
-	if (IS_DAX(iocb->ki_filp->f_mapping->host))
+	if (IS_DAX(inode))
 		return dax_iomap_rw(iocb, to, &erofs_iomap_ops);
 #endif
 	if (iocb->ki_flags & IOCB_DIRECT) {
-		int err = erofs_prepare_dio(iocb, to);
+		struct block_device *bdev = inode->i_sb->s_bdev;
+		unsigned int blksize_mask;
+
+		if (bdev)
+			blksize_mask = bdev_logical_block_size(bdev) - 1;
+		else
+			blksize_mask = (1 << inode->i_blkbits) - 1;
+
+		if ((iocb->ki_pos | iov_iter_count(to) |
+		     iov_iter_alignment(to)) & blksize_mask)
+			return -EINVAL;
 
-		if (!err)
-			return iomap_dio_rw(iocb, to, &erofs_iomap_ops,
-					    NULL, 0, NULL, 0);
-		if (err < 0)
-			return err;
+		return iomap_dio_rw(iocb, to, &erofs_iomap_ops,
+				    NULL, 0, NULL, 0);
 	}
 	return filemap_read(iocb, to, 0);
 }