title: Drbd device does not show up in lsblk
body: <p>I create two drbd block device, mount drbd1 as os disk to rootfs, drbd2 is planed to format in lxc. it works fine on ubuntu 16.04, lxc 2.x, drbd 8.4, centos6</p>
  <p>after upgrading the following software , lxc can still run, but drbd device don’t show up in lxc container.
  Who can give me some advice?</p>
  <pre><code># current config
  
  host: ubuntu 20.04 server
  lxc: 4.0.6
  lxc container: centos7 
  drbd version: 8.4
  /usr/share/lxc/config/common.conf is using default version 
  </code></pre>
  <p>limit in common.conf:</p>
  <p><a href="https://i.stack.imgur.com/KGpuj.png" rel="nofollow noreferrer">cgroup limit</a>
  <a href="https://i.stack.imgur.com/lEk8Q.png" rel="nofollow noreferrer">cgroup2 limit</a></p>
  <p>drbd block devices show up on host:</p>
  <pre><code>root@f1:/home/neo# lsblk
  NAME                      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
  loop1                       7:1    0 55.5M  1 loop /snap/core18/2246
  loop2                       7:2    0 61.9M  1 loop /snap/core20/1169
  loop3                       7:3    0 67.2M  1 loop /snap/lxd/21835
  loop4                       7:4    0 32.3M  1 loop /snap/snapd/12704
  loop5                       7:5    0 70.3M  1 loop /snap/lxd/21029
  loop6                       7:6    0 32.5M  1 loop /snap/snapd/13640
  loop7                       7:7    0 55.5M  1 loop /snap/core18/2253
  loop8                       7:8    0 61.9M  1 loop /snap/core20/1242
  sda                         8:0    0   32G  0 disk 
  ├─sda1                      8:1    0    1M  0 part 
  ├─sda2                      8:2    0    1G  0 part /boot
  └─sda3                      8:3    0   31G  0 part 
    └─ubuntu--vg-ubuntu--lv 253:0    0   30G  0 lvm  /
  sdb                         8:16   0   32G  0 disk 
  └─nevg1-nelv1             253:1    0   32G  0 lvm  
    └─drbd1                 147:1    0   32G  0 disk /mnt/test.neo
  sdc                         8:32   0   32G  0 disk 
  └─nevg2-nelv2             253:2    0   32G  0 lvm  
    └─drbd2                 147:2    0   32G  0 disk
  </code></pre>
  <p>drbd block devices don’t show up show up on lxc:</p>
  <pre><code>neo@f1:~$ sudo lxc-attach -n test.neo
  [root@test neo]# lsblk
  lsblk: dm-1: failed to get device path
  lsblk: dm-1: failed to get device path
  lsblk: dm-2: failed to get device path
  lsblk: dm-0: failed to get device path
  lsblk: dm-2: failed to get device path
  lsblk: dm-0: failed to get device path
  NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
  loop1    7:1    0 55.5M  1 loop 
  loop8    7:8    0 61.9M  1 loop 
  sdb      8:16   0   32G  0 disk 
  loop6    7:6    0 32.5M  1 loop 
  loop4    7:4    0 32.3M  1 loop 
  loop2    7:2    0 61.9M  1 loop 
  sdc      8:32   0   32G  0 disk 
  loop7    7:7    0 55.5M  1 loop 
  sda      8:0    0   32G  0 disk 
  |-sda2   8:2    0    1G  0 part 
  |-sda3   8:3    0   31G  0 part 
  `-sda1   8:1         1M  0 part 
  loop5    7:5    0 70.3M  1 loop 
  loop3    7:3    0 67.2M  1 loop 
  </code></pre>
  <p>but /proc/partitions show drbd block devices</p>
  <pre><code>[root@test neo]# cat /proc/partitions | grep drbd
   147        1   33549276 drbd1
   147        2   33549276 drbd2
  </code></pre>
  <p>this is lxc config:</p>
  <pre><code>lxc.net.0.type = phys
  lxc.net.0.link = ens20
  lxc.net.0.hwaddr = 66:79:48:3e:5b:b3
  lxc.net.0.flags = up
  lxc.net.0.ipv4.address = 172.20.6.25/24
  lxc.net.0.ipv4.gateway = 172.20.6.1
  lxc.net.0.name = eth0
  
  
  lxc.net.1.type = veth
  lxc.net.1.link = lxcbr0
  lxc.net.1.hwaddr = fe:54:34:0f:3a:5d
  lxc.net.1.flags = up
  lxc.net.1.ipv4.address = 169.254.0.102/24
  lxc.net.1.name = eth1
  
  lxc.rootfs.path = /mnt/test.neo
  
  lxc.include = /usr/share/lxc/config/common.conf
  
  lxc.arch = x86_64
  lxc.uts.name = test.neo
  </code></pre>