TRIM commands to null_blk device failing

Issue

• TRIM commands to null_blk device failing

[root@localhost ~]# fio --bs=128k --ioengine=libaio --iodepth=1024 --numjobs=4 --rw=randtrim --name=async --filename=/dev/nullb2 --size=2g
async: (g=0): rw=randtrim, bs=(R) 128KiB-128KiB, (W) 128KiB-128KiB, (T) 128KiB-128KiB, ioengine=libaio, iodepth=1024
...
fio-3.1
Starting 4 processes
async: No I/O performed by libaio, perhaps try --debug=io option for details?
fio: pid=12755, err=95/file:ioengines.c:333, func=td_io_queue, error=Operation not supported
async: No I/O performed by libaio, perhaps try --debug=io option for details?
fio: pid=12754, err=95/file:ioengines.c:333, func=td_io_queue, error=Operation not supported
async: No I/O performed by libaio, perhaps try --debug=io option for details?
fio: pid=12751, err=95/file:ioengines.c:333, func=td_io_queue, error=Operation not supported
async: No I/O performed by libaio, perhaps try --debug=io option for details?
fio: pid=12753, err=95/file:ioengines.c:333, func=td_io_queue, error=Operation not supported