External bind mounts

Typical external resource when dumping a container (especially LXC/Docker) -- is a mount point whose root sits outside of the container's root. This situation was intended to be resolved using plugins but turned out to be so frequent, that we introduced a non-plugin way of handling them.

What is external bind mount

The way to create such is simple as

mkdir /root
mount --bind /foo /root/bar
chroot /root

This is it. From now on, the /bar file is a mountpoint whose root (the source) is not accessible directly.

If you look at the /proc/$pid/mountinfo file of a task seeing such you would see smth like

11 23 8:3 /root / ... - ext4 /dev/sda1 ...
23 34 8:3 /foo /bar ... - ext4 /dev/sda1 ...

The columns 4 and 5 are root and mountpoint respectively. You can see, that the / is /root file from /dev/sda1 device and /bar file is a mountpoint with the root being /foo file from the same device.