ext4: restructure ext4_ext_direct_IO()

Remove a level of indentation by moving the DIO read and extending
write case to the beginning of the file.  This results in no actual
programmatic changes to the file, but makes it easier to
read/understand.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/inode.c

@@ -2927,10 +2927,10 @@ static int ext4_set_bh_endio(struct buffer_head *bh, struct inode *inode)
  * fall back to buffered IO.
  *
  * For holes, we fallocate those blocks, mark them as uninitialized
- * If those blocks were preallocated, we mark sure they are splited, but
+ * If those blocks were preallocated, we mark sure they are split, but
  * still keep the range to write as uninitialized.
  *
- * The unwrritten extents will be converted to written when DIO is completed.
+ * The unwritten extents will be converted to written when DIO is completed.
  * For async direct IO, since the IO may still pending when return, we
  * set up an end_io call back function, which will do the conversion
  * when async direct IO completed.
@@ -2948,125 +2948,120 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
 	struct inode *inode = file->f_mapping->host;
 	ssize_t ret;
 	size_t count = iov_length(iov, nr_segs);
-
+	int overwrite = 0;
+	get_block_t *get_block_func = NULL;
+	int dio_flags = 0;
 	loff_t final_size = offset + count;
-	if (rw == WRITE && final_size <= inode->i_size) {
-		int overwrite = 0;
-		get_block_t *get_block_func = NULL;
-		int dio_flags = 0;
 
-		BUG_ON(iocb->private == NULL);
+	/* Use the old path for reads and writes beyond i_size. */
+	if (rw != WRITE || final_size > inode->i_size)
+		return ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);
 
-		/* If we do a overwrite dio, i_mutex locking can be released */
-		overwrite = *((int *)iocb->private);
+	BUG_ON(iocb->private == NULL);
 
-		if (overwrite) {
-			atomic_inc(&inode->i_dio_count);
-			down_read(&EXT4_I(inode)->i_data_sem);
-			mutex_unlock(&inode->i_mutex);
-		}
+	/* If we do a overwrite dio, i_mutex locking can be released */
+	overwrite = *((int *)iocb->private);
 
-		/*
- 		 * We could direct write to holes and fallocate.
-		 *
- 		 * Allocated blocks to fill the hole are marked as uninitialized
- 		 * to prevent parallel buffered read to expose the stale data
- 		 * before DIO complete the data IO.
-		 *
- 		 * As to previously fallocated extents, ext4 get_block
- 		 * will just simply mark the buffer mapped but still
- 		 * keep the extents uninitialized.
- 		 *
-		 * for non AIO case, we will convert those unwritten extents
-		 * to written after return back from blockdev_direct_IO.
-		 *
-		 * for async DIO, the conversion needs to be defered when
-		 * the IO is completed. The ext4 end_io callback function
-		 * will be called to take care of the conversion work.
-		 * Here for async case, we allocate an io_end structure to
-		 * hook to the iocb.
- 		 */
-		iocb->private = NULL;
-		ext4_inode_aio_set(inode, NULL);
-		if (!is_sync_kiocb(iocb)) {
-			ext4_io_end_t *io_end =
-				ext4_init_io_end(inode, GFP_NOFS);
-			if (!io_end) {
-				ret = -ENOMEM;
-				goto retake_lock;
-			}
-			io_end->flag |= EXT4_IO_END_DIRECT;
-			iocb->private = io_end;
-			/*
-			 * we save the io structure for current async
-			 * direct IO, so that later ext4_map_blocks()
-			 * could flag the io structure whether there
-			 * is a unwritten extents needs to be converted
-			 * when IO is completed.
-			 */
-			ext4_inode_aio_set(inode, io_end);
-		}
+	if (overwrite) {
+		atomic_inc(&inode->i_dio_count);
+		down_read(&EXT4_I(inode)->i_data_sem);
+		mutex_unlock(&inode->i_mutex);
+	}
 
-		if (overwrite) {
-			get_block_func = ext4_get_block_write_nolock;
-		} else {
-			get_block_func = ext4_get_block_write;
-			dio_flags = DIO_LOCKING;
+	/*
+	 * We could direct write to holes and fallocate.
+	 *
+	 * Allocated blocks to fill the hole are marked as
+	 * uninitialized to prevent parallel buffered read to expose
+	 * the stale data before DIO complete the data IO.
+	 *
+	 * As to previously fallocated extents, ext4 get_block will
+	 * just simply mark the buffer mapped but still keep the
+	 * extents uninitialized.
+	 *
+	 * For non AIO case, we will convert those unwritten extents
+	 * to written after return back from blockdev_direct_IO.
+	 *
+	 * For async DIO, the conversion needs to be deferred when the
+	 * IO is completed. The ext4 end_io callback function will be
+	 * called to take care of the conversion work.  Here for async
+	 * case, we allocate an io_end structure to hook to the iocb.
+	 */
+	iocb->private = NULL;
+	ext4_inode_aio_set(inode, NULL);
+	if (!is_sync_kiocb(iocb)) {
+		ext4_io_end_t *io_end = ext4_init_io_end(inode, GFP_NOFS);
+		if (!io_end) {
+			ret = -ENOMEM;
+			goto retake_lock;
 		}
-		ret = __blockdev_direct_IO(rw, iocb, inode,
-					 inode->i_sb->s_bdev, iov,
-					 offset, nr_segs,
-					 get_block_func,
-					 ext4_end_io_dio,
-					 NULL,
-					 dio_flags);
-
-		if (iocb->private)
-			ext4_inode_aio_set(inode, NULL);
+		io_end->flag |= EXT4_IO_END_DIRECT;
+		iocb->private = io_end;
 		/*
-		 * The io_end structure takes a reference to the inode,
-		 * that structure needs to be destroyed and the
-		 * reference to the inode need to be dropped, when IO is
-		 * complete, even with 0 byte write, or failed.
-		 *
-		 * In the successful AIO DIO case, the io_end structure will be
-		 * desctroyed and the reference to the inode will be dropped
-		 * after the end_io call back function is called.
-		 *
-		 * In the case there is 0 byte write, or error case, since
-		 * VFS direct IO won't invoke the end_io call back function,
-		 * we need to free the end_io structure here.
+		 * we save the io structure for current async direct
+		 * IO, so that later ext4_map_blocks() could flag the
+		 * io structure whether there is a unwritten extents
+		 * needs to be converted when IO is completed.
 		 */
-		if (ret != -EIOCBQUEUED && ret <= 0 && iocb->private) {
-			ext4_free_io_end(iocb->private);
-			iocb->private = NULL;
-		} else if (ret > 0 && !overwrite && ext4_test_inode_state(inode,
-						EXT4_STATE_DIO_UNWRITTEN)) {
-			int err;
-			/*
-			 * for non AIO case, since the IO is already
-			 * completed, we could do the conversion right here
-			 */
-			err = ext4_convert_unwritten_extents(inode,
-							     offset, ret);
-			if (err < 0)
-				ret = err;
-			ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
-		}
+		ext4_inode_aio_set(inode, io_end);
+	}
 
-	retake_lock:
-		/* take i_mutex locking again if we do a ovewrite dio */
-		if (overwrite) {
-			inode_dio_done(inode);
-			up_read(&EXT4_I(inode)->i_data_sem);
-			mutex_lock(&inode->i_mutex);
-		}
+	if (overwrite) {
+		get_block_func = ext4_get_block_write_nolock;
+	} else {
+		get_block_func = ext4_get_block_write;
+		dio_flags = DIO_LOCKING;
+	}
+	ret = __blockdev_direct_IO(rw, iocb, inode,
+				   inode->i_sb->s_bdev, iov,
+				   offset, nr_segs,
+				   get_block_func,
+				   ext4_end_io_dio,
+				   NULL,
+				   dio_flags);
+
+	if (iocb->private)
+		ext4_inode_aio_set(inode, NULL);
+	/*
+	 * The io_end structure takes a reference to the inode, that
+	 * structure needs to be destroyed and the reference to the
+	 * inode need to be dropped, when IO is complete, even with 0
+	 * byte write, or failed.
+	 *
+	 * In the successful AIO DIO case, the io_end structure will
+	 * be destroyed and the reference to the inode will be dropped
+	 * after the end_io call back function is called.
+	 *
+	 * In the case there is 0 byte write, or error case, since VFS
+	 * direct IO won't invoke the end_io call back function, we
+	 * need to free the end_io structure here.
+	 */
+	if (ret != -EIOCBQUEUED && ret <= 0 && iocb->private) {
+		ext4_free_io_end(iocb->private);
+		iocb->private = NULL;
+	} else if (ret > 0 && !overwrite && ext4_test_inode_state(inode,
+						EXT4_STATE_DIO_UNWRITTEN)) {
+		int err;
+		/*
+		 * for non AIO case, since the IO is already
+		 * completed, we could do the conversion right here
+		 */
+		err = ext4_convert_unwritten_extents(inode,
+						     offset, ret);
+		if (err < 0)
+			ret = err;
+		ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
+	}
 
-		return ret;
+retake_lock:
+	/* take i_mutex locking again if we do a ovewrite dio */
+	if (overwrite) {
+		inode_dio_done(inode);
+		up_read(&EXT4_I(inode)->i_data_sem);
+		mutex_lock(&inode->i_mutex);
 	}
 
-	/* for write the the end of file case, we fall back to old way */
-	return ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);
+	return ret;
 }
 
 static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,