Comment # 7 on bug 1127701 from Stanislav Brabec

It seems that use of mnt_context makes only a little sense for the rest of
fstrim_all() (and for the rest of the fstrim, we don't need these structures at
all).

Additionally, we cannot use mnt_context_prepare_srcpath() anyway. In case of
loop device inside fstab, it is going to initialize the loop device again,
which would be pretty ugly, even if recent libmount has a loop dep-duplication
code.

It complicates 1. and 4.

So 2. or 3. seems to be the best solution. I am trying to finish 3.