[SPDK] vhost_blk on logical volume appears 0 size in QEMU

Hi could someone help me a little ? 
I'm trying to deploy vhost-user on QEMU, and the virtual block device in QEMU shows that it has a size of 0B. 
Here's how I do this:
1. create lvstore on one NVME SSD
2. create five logical volume from the lvstore (evenly sliced).
3. attach all five logical volumes to five vhost controllers separately.
4. launch QEMU with vhost-user-blk-pci enabled

then in the VM, when I lsblk , I find that all of the vdx devices have a size of 0B.
Is this a bug or did I do this wrong?

Thank you