fix leftover bytes calculation

If there are leftovers __end_that_request_first will call blk_recalc_rq_sector to set req->hard_nr_sectors correctly. For failfast, by subtracting bytes from the updated req->hard_nr_sectors and then calling end_that_request_chunk and end_that_request_last, you can end up with a bio that never gets completed.

The attached patch built against 2.6.4 does not subtract bytes for non-blk_pc_requests.

On a related note I was wondering if the following is a bug or feature. At the bottom of scsi_io_completion, it calls scsi_end_request on the bytes for the current buffer. The comments indicate this is to handle improperly reported medium errors, but commands scsi_decide_disposition determined should not be retried end up getting requeued minus the current buffer.

Thanks

Mike Christie

@@ -504,7 +504,7 @@ static struct scsi_cmnd *scsi_end_reques
 	 * to queue the remainder of them.
 	 */
 	if (end_that_request_chunk(req, uptodate, bytes)) {
-		int leftover = (req->hard_nr_sectors << 9) - bytes;
+		int leftover = req->hard_nr_sectors << 9;
 
 		if (blk_pc_request(req))
 			leftover = req->data_len - bytes;

Oh wait, forget that. I wasn't sure if those medium errors described in the comments were incorrectly reported as any old error or if there was some way to narrow it down.