From: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Date: Mon, 8 Aug 2016 17:27:31 +0000 (+0900)
Subject: Check if sysfs ioscheduler entry is "none"
X-Git-Tag: fio-2.14~44
X-Git-Url: https://git.kernel.dk/?p=fio.git;a=commitdiff_plain;h=67f28a8cf74bf64c1c35fde49a425d62bb143fa8

Check if sysfs ioscheduler entry is "none"

Block devices without elevator (bio-based-dm/loop/etc) have "none"
for sysfs ioscheduler tunable, and write to this entry never fail
from the way elv_iosched_store() is implemented.

This commit checks if the entry is "none" type so as not to show
an irrelevant error message which assumes the entry has a list of
available I/O schedulers.

 # cat /sys/block/dm-0/queue/scheduler
 none
 # echo deadline > /sys/block/dm-0/queue/scheduler ; echo $?
 0
 # cat /sys/block/dm-0/queue/scheduler
 none
 # echo aaa > /sys/block/dm-0/queue/scheduler ; echo $?
 0
 # cat /sys/block/dm-0/queue/scheduler
 none

Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
---

diff --git a/backend.c b/backend.c
index 58727114..6bf5d679 100644
--- a/backend.c
+++ b/backend.c
@@ -1331,6 +1331,14 @@ static int switch_ioscheduler(struct thread_data *td)
 	 */
 	tmp[strlen(tmp) - 1] = '\0';
 
+	/*
+	 * Write to "none" entry doesn't fail, so check the result here.
+	 */
+	if (!strcmp(tmp, "none")) {
+		log_err("fio: io scheduler is not tunable\n");
+		fclose(f);
+		return 0;
+	}
 
 	sprintf(tmp2, "[%s]", td->o.ioscheduler);
 	if (!strstr(tmp, tmp2)) {