On Mon, Apr 18, 2022 at 5:54 PM Chaitanya Kulkarni <chaitanyak@xxxxxxxxxx> wrote: > > On 4/18/22 14:38, Josef Bacik wrote: > > Hello, > > > > I'm trying to add a test to fsperf and it requires the use of nullblk. I'm > > trying to use the configfs thing, and it's doing some odd things. My basic > > reproducer is > > > > modprobe null_blk > > mkdir /sys/kernel/config/nullb/nullb0 > > echo some shit into the config > > echo 1 > /sys/kernel/config/nullb/nullb0/power > > > > Now null_blk apparently defaults to nr_devices == 1, so it creates nullb0 on > > modprobe. But this doesn't show up in the configfs directory. There's no way > > to find this out until when I try to mkfs my nullb0 and it doesn't work. The > > above steps gets my device created at /dev/nullb1, but there's no actual way to > > figure out that's what happened. If I do something like > > /sys/kernel/config/nullb/nullbfsperf I still just get nullb<number>, I don't get > > my fancy name. > > > > when you load module with default module parameter it will create a > default device with no memory backed mode, that will not be visible in > the configfs. > > So you need to load the module with nr_devices=0 that will prevent the > null_blk to create the default device which is not memory backed and not > present in the configfs:- > Yup I know what it's doing, I'm raising this as it's weird and took me a bit to work out what was happening, and it annoyed me. It's not anything I can't work around, but the UX kinda sucks. Thanks, Josef
