On rare occasions, when trying to mount a file system via the
loopback device that was created in the stage before the mount
fails with `wrong fs type, bad option, bad superblock on ...`.
It is not yet fully clear why this appears since in theory the
kernel should handle the sequence of operations we do, but it
might be down to the caching or bugs in the underlying file-
system.
To mitigate with potential caching issue we therefore now sync
the file that is backing the loopback device after the device
has been closed. In order to not have to re-open the file we
keep the file descriptor around as long as the loopback device
is open.
Device service that provides support for bind files within the tree
to loopback devices. Valid parameters are the `filename`, `offset`
and `size`. This controls what part of the file to bind to the loop
device. The unit for `size` and `offset` is sectors and the sector
size can be configured via the `sector-size` parameter. The reason
behind the sector unit is so that numbers can easily be compared
with those specified in the partition table.
