idmap fail with filesystem type='block'

gistfile1.txt

# virsh dumpxml sew02
<domain type='lxc'>
  <name>sew02</name>
  <uuid>18f76f2f-0852-434c-8a3d-18a56ffdf33b</uuid>
  <memory unit='KiB'>65536</memory>
  <currentMemory unit='KiB'>65536</currentMemory>
  <vcpu placement='static'>1</vcpu>
  <resource>
    <partition>/machine</partition>
  </resource>
  <os>
    <type arch='x86_64'>exe</type>
    <init>/sbin/init</init>
  </os>
  <idmap>
    <uid start='0' target='10000' count='2000'/>
    <gid start='0' target='10000' count='2000'/>
  </idmap>
  <features>
    <privnet/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>/usr/lib/libvirt_lxc</emulator>
    <filesystem type='block' accessmode='passthrough'>
      <source dev='/dev/instances/sew02'/>
      <target dir='/'/>
    </filesystem>
    <filesystem type='mount' accessmode='passthrough'>
      <source dir='/sys/fs/fuse/connections'/>
      <target dir='/sys/fs/fuse/connections'/>
    </filesystem>
    <interface type='network'>
      <mac address='52:54:00:64:1b:2a'/>
      <source network='br1'/>
    </interface>
    <console type='pty'>
      <target type='lxc' port='0'/>
    </console>
  </devices>
</domain>

# virsh start sew02
error: Failed to start domain sew02
error: internal error: guest failed to start: Failed to mount device /dev/dm-1 to /var/run/libvirt/lxc/sew02.root: Operation not permitted
0x7f085a52a160 0x7f085a529500