Description of problem:

Check packed option it should support with device vhost-user-blk-pci
The guest/qemu boot failed with unfriendly prompt message：
#(qemu) qemu-storage-daemon: vu_panic: virtio: zero sized buffers are not allowed
#qemu-kvm: Failed to set msg fds.
#qemu-kvm: vhost VQ 0 ring restore failed: -1: Input/output error (5)


vhost-user-blk-pci options:
  addr=<int32>           - Slot and optional function number, example: 06.0 or 06 (default: -1)
  any_layout=<bool>      - on/off (default: true)
  ats=<bool>             - on/off (default: false)
  bootindex=<int32>
  chardev=<str>          - ID of a chardev to use as a backend
  class=<uint32>         -  (default: 0)
  config-wce=<bool>      - on/off (default: true)
  disable-legacy=<OnOffAuto> - on/off/auto (default: "auto")
  disable-modern=<bool>  -  (default: false)
  event_idx=<bool>       - on/off (default: true)
  failover_pair_id=<str>
  indirect_desc=<bool>   - on/off (default: true)
  iommu_platform=<bool>  - on/off (default: false)
  migrate-extra=<bool>   - on/off (default: true)
  modern-pio-notify=<bool> - on/off (default: false)
  multifunction=<bool>   - on/off (default: false)
  notify_on_empty=<bool> - on/off (default: true)
  num-queues=<uint16>    -  (default: 65535)
  packed=<bool>          - on/off (default: false)
  page-per-vq=<bool>     - on/off (default: false)
  queue-size=<uint32>    -  (default: 128)


Version-Release number of selected component (if applicable):
Red Hat Enterprise Linux release 8.4 Beta (Ootpa)
4.18.0-291.el8.x86_64
qemu-kvm-common-5.2.0-9.module+el8.4.0+10182+4161bd91.x86_64

How reproducible:
100%

Steps to Reproduce:
1.create images if they are inexist
qemu-img create -f qcow2 /home/kvm_autotest_root/images/disk1.qcow2 1G
qemu-img create -f qcow2 /home/kvm_autotest_root/images/disk2.qcow2 1G


2.export them with qsd

qemu-storage-daemon \
  --chardev socket,path=/tmp/qmp.sock,server,nowait,id=char1 \
  --monitor chardev=char1 \
  --object iothread,id=iothread0 \
  --blockdev driver=file,node-name=file1,filename=/home/kvm_autotest_root/images/disk1.qcow2 \
  --blockdev driver=qcow2,node-name=fmt1,file=file1 \
  --export type=vhost-user-blk,id=export1,addr.type=unix,addr.path=/tmp/vhost-user-blk1.sock,node-name=fmt1,writable=on,iothread=iothread0 \
  --blockdev driver=file,node-name=file2,filename=/home/kvm_autotest_root/images/disk2.qcow2\
  --blockdev driver=qcow2,node-name=fmt2,file=file2 \
  --export type=vhost-user-blk,id=export2,addr.type=unix,addr.path=/tmp/vhost-user-blk2.sock,node-name=fmt2,writable=on,iothread=iothread0 

3.boot qemu with vhost-user-blk-pci device
/usr/libexec/qemu-kvm -enable-kvm \
  -m 4G -M q35,accel=kvm,memory-backend=mem,kernel-irqchip=split \
  -nodefaults \
  -vga qxl \
  -cpu host,+kvm_pv_unhalt \
  -smp 4 \
  -device intel-iommu,device-iotlb=on,intremap \
  -object memory-backend-memfd,id=mem,size=4G,share=on \
  -device pcie-root-port,id=pcie-root-port-0,multifunction=on,bus=pcie.0,addr=0x3,chassis=1 \
  -device pcie-root-port,id=pcie-root-port-1,port=0x1,addr=0x3.0x1,bus=pcie.0,chassis=2 \
  -device pcie-root-port,id=pcie-root-port-2,port=0x2,addr=0x3.0x2,bus=pcie.0,chassis=3 \
  -device pcie-root-port,id=pcie-root-port-3,port=0x3,addr=0x3.0x3,bus=pcie.0,chassis=4 \
  -device pcie-root-port,id=pcie-root-port-4,port=0x4,addr=0x3.0x4,bus=pcie.0,chassis=5 \
  -device pcie-root-port,id=pcie-root-port-5,port=0x5,addr=0x3.0x5,bus=pcie.0,chassis=6 \
  -device pcie-root-port,id=pcie-root-port-6,port=0x6,addr=0x3.0x6,bus=pcie.0,chassis=7 \
  -device pcie-root-port,id=pcie-root-port-7,port=0x7,addr=0x3.0x7,bus=pcie.0,chassis=8 \
  -device qemu-xhci,id=usb1,bus=pcie-root-port-1,addr=0x0 \
  -device usb-tablet,id=usb-tablet1,bus=usb1.0,port=1 \
  -device virtio-scsi-pci,id=scsi0,bus=pcie-root-port-5 \
  -device virtio-scsi-pci,id=scsi1,bus=pcie-root-port-6 \
  -blockdev driver=qcow2,file.driver=file,file.filename=/home/kvm_autotest_root/images/rhel840-64-virtio-scsi.qcow2,node-name=os_image1 \
  -device virtio-blk-pci,id=blk0,drive=os_image1,bootindex=0 \
  \
  -chardev socket,path=/tmp/vhost-user-blk1.sock,id=vhost1 \
  -device vhost-user-blk-pci,chardev=vhost1,id=blk1,bus=pcie-root-port-3,addr=0x0,num-queues=1,bootindex=1,packed=on \
  \
  -vnc :5 \
  -monitor stdio \
  -qmp tcp:0:5955,server,nowait

Actual results:
guest boot failed
Expected results:
if this feature not support it should removed from the options or give user friendly message.

Additional info: