#!/bin/sh

set -e

if [ "$1" = configure ]; then
    # A dependent library of Upstart has changed, so restart Upstart
    # such that it can safely unmount the root filesystem (LP: #740390)

    # Query running version of Upstart, but only when we know
    # that initctl will work.
    #
    # The calculated version string may be the null string if
    # Upstart is not running (where for example an alternative
    # init is running outside a chroot environment) or if the
    # query failed for some reason. However, the version check
    # below handles a null version string correctly.
    UPSTART_VERSION_RUNNING=$(initctl version 2>/dev/null |\
        awk '{print $3}'|tr -d ')' || :)

    if ischroot; then
        # Do not honour re-exec when requested from within a
        # chroot since:
        #
        # (a) The version of Upstart outside might not support it.
        # (b) An isolated environment such as a chroot should
        #     not be able to modify its containing environment.
        #
        # A sufficiently new Upstart will actually handle a re-exec
        # request coming from telinit within a chroot correctly (by
        # doing nothing) but it's simple enough to perform the check
        # here and save Upstart the effort.
        :
    elif dpkg --compare-versions "$UPSTART_VERSION_RUNNING" ge 1.6.1; then
        # We are not running inside a chroot and the running version
        # of Upstart supports stateful re-exec, so we can
        # restart immediately.
        #
        # XXX: Note that the check on the running version must
        # remain *indefinitely* since it's the only safe way to
        # know if stateful re-exec is supported: simply checking
        # packaged version numbers is not sufficient since
        # the package could be upgraded multiple times without a
        # reboot.
        telinit u || :
    else
        # Before we shutdown or reboot, we need to re-exec so that we
        # can safely remount the root filesystem; we can't just do that
        # here because we lose state.
        touch /var/run/init.upgraded || :
    fi
fi