blk-mq: should elv_iosched_store return ENXIO/EINVAL?

Sebastian Herbszt
2014-12-30T23:37:17Z

Hello,

setting an invalid elevator without blk-mq results in an error:

# cat /sys/block/sda/queue/scheduler
noop deadline [cfq]
# echo foo > /sys/block/sda/queue/scheduler
-bash: echo: write error: Invalid argument
# dmesg
[ 328.767088] elevator: type foo not found
[ 328.767097] elevator: switch to foo
failed

With blk-mq no error is returned:

# cat /sys/block/sda/queue/scheduler
none
# echo foo > /sys/block/sda/queue/scheduler
# echo $?
0

block/elevator.c got

988 ssize_t elv_iosched_store(struct request_queue *q, const char *name,
989 size_t count)
990 {
991 int ret;
992
993 if (!q->elevator)
994 return count;
995
996 ret = __elevator_change(q, name);

and

952 static int __elevator_change(struct request_queue *q, const char *name)
953 {
954 char elevator_name[ELV_NAME_MAX];
955 struct elevator_type *e;
956
957 if (!q->elevator)
958 return -ENXIO;
959
960 strlcpy(elevator_name, name, sizeof(elevator_name));
961 e = elevator_get(strstrip(elevator_name), true);
962 if (!e) {
963 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
964 return -EINVAL;
965 }

So !q->elevator is checked in elv_iosched_store and __elevator_change.

Should elv_iosched_store return ENXIO or EINVAL or should __elevator_change
handle this?

Sebastian