functions for mounting, umounting, parsing /proc/mounts, etc
canonicalised, absolute path
|-> IO [(FilePath, (String, String, ExitCode))]|
paths that we attempted to umount, and the responding output from the umount command
umountBelow - unmounts all mount points below belowPath
/proc/mounts must be present and readable. Because of the way
linux handles changeroots, we can't trust everything we see in
/proc/mounts. However, we make the following assumptions:
- there is a one-to-one correspondence between the entries in /proc/mounts and the actual mounts, and (2) every mount point we might encounter is a suffix of one of the mount points listed in /proc/mounts (because being in a a chroot doesn't affect /proc/mounts.)
So we can search /proc/mounts for an entry has the mount point we are looking for as a substring, then add the extra text on the right to our path and try to unmount that. Then we start again since nested mounts might have been revealed.
For example, suppose we are chrooted into /home/david/environments/sid and we call umountBelow /proc. We might see the mount point /home/david/environments/sid/proc/bus/usb in /proc/mounts, which means we need to run umount /proc/bus/usb.
umount - run umount with the specified args
NOTE: this function uses exec, so you do not need to shell-escape
NOTE: we don't use the umount system call because the system call
is not smart enough to update /etc/mtab