It says: The prefix path **must be absolute, have all symlinks resolved, and cleaned**. But those requirements are violated in lots of places.
What happens when it is given a non-canonicalized path is that `mountinfo.GetMounts` will not find mounts.
The trivial case is:
```
$ mkdir a && ln -s a b && mkdir b/c b/d && mount --bind b/c b/d && cat /proc/mounts | grep -- '[ab]/d'
/dev/sdd3 /home/user/a/d ext4 rw,noatime,discard 0 0
```
We asked to bind-mount b/c to b/d, but ended up with mount in a/d.
So, mount table always contains canonicalized mount points, and it is an error to look for non-canonicalized paths in it.
Signed-off-by: Marat Radchenko <marat@slonopotamus.org>
