block: Warn if elevator= parameter is used

With transition to blk-mq, the elevator= kernel argument was removed as
it makes less and less sense with the current variety of devices.  Since
this may surprise some users and there are advices on the Internet that
still suggest to use it, let's at least warn if the parameter is used.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/elevator.c b/block/elevator.c
index 5437059c92615ea9c474342d31ad4348e788bf19..0b1db9afb5867c2d55f5cd0aadff69ba877569bf 100644 (file)
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -831,3 +831,12 @@ struct request *elv_rb_latter_request(struct request_queue *q,
        return NULL;
 }
 EXPORT_SYMBOL(elv_rb_latter_request);
+
+static int __init elevator_setup(char *str)
+{
+       pr_warn("Kernel parameter elevator= does not have any effect anymore.\n"
+               "Please use sysfs to set IO scheduler for individual devices.\n");
+       return 1;
+}
+
+__setup("elevator=", elevator_setup);