udf_file_write_iter: reorder and simplify

it's easier to do generic_write_checks() first
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/udf/file.c

@@ -120,21 +120,27 @@ static ssize_t udf_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	ssize_t retval;
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file_inode(file);
-	int err, pos;
 	size_t count = iov_iter_count(from);
 	struct udf_inode_info *iinfo = UDF_I(inode);
+	int err;
 
 	mutex_lock(&inode->i_mutex);
+
+	retval = generic_write_checks(file, &iocb->ki_pos, &count);
+	if (retval)
+		goto out;
+
+	if (count == 0)
+		goto out;
+
+	iov_iter_truncate(from, count);
+
 	down_write(&iinfo->i_data_sem);
 	if (iinfo->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB) {
-		if (file->f_flags & O_APPEND)
-			pos = inode->i_size;
-		else
-			pos = iocb->ki_pos;
+		loff_t end = iocb->ki_pos + iov_iter_count(from);
 
 		if (inode->i_sb->s_blocksize <
-				(udf_file_entry_alloc_offset(inode) +
-						pos + count)) {
+				(udf_file_entry_alloc_offset(inode) + end)) {
 			err = udf_expand_file_adinicb(inode);
 			if (err) {
 				mutex_unlock(&inode->i_mutex);
@@ -142,24 +148,12 @@ static ssize_t udf_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 				return err;
 			}
 		} else {
-			if (pos + count > inode->i_size)
-				iinfo->i_lenAlloc = pos + count;
-			else
-				iinfo->i_lenAlloc = inode->i_size;
+			iinfo->i_lenAlloc = max(end, inode->i_size);
 			up_write(&iinfo->i_data_sem);
 		}
 	} else
 		up_write(&iinfo->i_data_sem);
 
-	retval = generic_write_checks(file, &iocb->ki_pos, &count);
-	if (retval)
-		goto out;
-
-	if (count == 0)
-		goto out;
-
-	iov_iter_truncate(from, count);
-
 	retval = __generic_file_write_iter(iocb, from);
 out:
 	mutex_unlock(&inode->i_mutex);