[lmi] Where can I find the urtext of mount data?

[Greg Chicares]

Vadim--After this command:

mount --rbind /var/cache/centos_lmi /srv/chroot/centos7lmi/var/cache/yum

I observe:

$mount |grep yum                                          
/dev/sdb5 on /srv/chroot/centos7lmi/var/cache/yum type ext4 
(rw,relatime,errors=remount-ro)
$grep yum /proc/mounts                           
/dev/sdb5 /srv/chroot/centos7lmi/var/cache/yum ext4 
rw,relatime,errors=remount-ro 0 0
$findmnt /srv/chroot/centos7lmi/var/cache/yum             
TARGET                               SOURCE                           FSTYPE 
OPTIONS
/srv/chroot/centos7lmi/var/cache/yum /dev/sdb5[/var/cache/centos_lmi] ext4   
rw,relatime,errors=rem

How does findmnt know that the "device" is really
  /dev/sdb5[/var/cache/centos_lmi]
when /proc/mounts seems to think it's just /dev/sdb5 ?

I thought /proc/mounts was supposed to be the definitive repository
of mount information, so does findmnt get this extra information:
  [/var/cache/centos_lmi]
from some more definitive source?