From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 13 Mar 2018 17:49:55 +0000 (-0600)
Subject: io_u: only rewind file position if it's non-zero
X-Git-Tag: fio-3.6~40
X-Git-Url: https://git.kernel.dk/?p=fio.git;a=commitdiff_plain;h=69b98f11d62cb12482130fac79b8ebf00c0bb139;ds=sidebyside

io_u: only rewind file position if it's non-zero

This:

bs=8k
rw=read:-4k

is supposed to read 0..8k, then add 8k and subtract 4k, ending
up with a next read at 4k..12k and so forth. But we rewind too
quickly, and the first IO fails as being out-of-bounds.

Fixes: c22825bb537af ("Fix backwards reads with --size smaller than the file size")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/io_u.c b/io_u.c
index a37b723e..01b36938 100644
--- a/io_u.c
+++ b/io_u.c
@@ -430,7 +430,11 @@ static int get_next_seq_offset(struct thread_data *td, struct fio_file *f,
 	if (f->last_pos[ddir] < f->real_file_size) {
 		uint64_t pos;
 
-		if (f->last_pos[ddir] == f->file_offset && o->ddir_seq_add < 0) {
+		/*
+		 * Only rewind if we already hit the end
+		 */
+		if (f->last_pos[ddir] == f->file_offset &&
+		    f->file_offset && o->ddir_seq_add < 0) {
 			if (f->real_file_size > f->io_size)
 				f->last_pos[ddir] = f->io_size;
 			else