[PATCH] Direct IO async short read fix

The direct I/O code is mapping the read request to the file system block. If
the file size was not on a block boundary, the result would show the the read
reading past EOF. This was only happening for the AIO case. The non-AIO case
truncates the result to match file size (in direct_io_worker). This patch
does the same thing for the AIO case, it truncates the result to match the
file size if the read reads past EOF.

When I/O completes the result can be truncated to match the file size
without using i_size_read(), thus the aio result now matches the number of
bytes read to the end of file.

Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/direct-io.c

···
 	struct bio *bio;		/* bio under assembly */
 	struct inode *inode;
 	int rw;
+	loff_t i_size;			/* i_size when submitted */
 	int lock_type;			/* doesn't change */
 	unsigned blkbits;		/* doesn't change */
 	unsigned blkfactor;		/* When we're using an alignment which
···
 	spin_lock_irqsave(&dio->bio_lock, flags);
 	if (dio->bio_count == 1) {
 		if (dio->is_async) {
+			ssize_t transferred;
+			loff_t offset;
+
 			/*
 			 * Last reference to the dio is going away.
 			 * Drop spinlock and complete the DIO.
 			 */
 			spin_unlock_irqrestore(&dio->bio_lock, flags);
-			dio_complete(dio, dio->block_in_file << dio->blkbits,
-					dio->result);
+
+			/* Check for short read case */
+			transferred = dio->result;
+			offset = dio->iocb->ki_pos;
+
+			if ((dio->rw == READ) &&
+			    ((offset + transferred) > dio->i_size))
+				transferred = dio->i_size - offset;
+
+			dio_complete(dio, offset, transferred);
+
 			/* Complete AIO later if falling back to buffered i/o */
 			if (dio->result == dio->size ||
 				((dio->rw == READ) && dio->result)) {
-				aio_complete(dio->iocb, dio->result, 0);
+				aio_complete(dio->iocb, transferred, 0);
 				kfree(dio);
 				return;
 			} else {
···
 	dio->page_errors = 0;
 	dio->result = 0;
 	dio->iocb = iocb;
+	dio->i_size = i_size_read(inode);
 
 	/*
 	 * BIO completion state.