#!/bin/sh
# (c) 2008 Quest Software, Inc. All rights reserved.
# This file's licence text is at the bottom of the file.
# By Ted Percival <ted@midg3t.net>

set -e

# Where the virtual machine chroots are
# Do not include the trailing slash
VMDIR=/srv/vm
PREFERRED_SHELL=/bin/bash
FALLBACK_SHELL=/bin/sh

die () {
    echo "$@" >&2
    exit 1
}

if [ $# -lt 1 ]; then
    echo "Usage: $0 <chrootname>" >&2
    echo " or $0 -l to list available chroots" >&2
    echo " or $0 -r <chrootname> to unmount the given chroot" >&2
    echo " or $0 -m <chrootname> to mount the chroot directories but not " >&2
    echo "          actually execute a shell in the chroot" >&2
    exit 1
fi

# Mounts all known directories for the given chroot
mount_dirs () {
    test -d "$VMDIR/$1" || die "mount_dirs: $VMDIR/$1 is not a directory"

    # Ensure the directory is slash-terminated, so if there are entries like
    # 4.0-etch and 4.0-etch-gtk, specifying the first will not match the second
    case "$1" in
	*/);;
	*) set -- "$1/";;
    esac

    # Find all the mounts in fstab that belong to this chroot
    dirs=`grep -v '^#' < /etc/fstab | awk '{print $2}' | grep -- "^$VMDIR" | grep -- "$1"`
    for dir in $dirs; do
	sudo mount $dir >/dev/null 2>&1 || echo "WARNING: Failed to mount $dir, is it already mounted?" >&2
    done
}

# Unmounts known directories for the given chroot
# Pass a single chroot name (directory)
unmount_dirs () {
    test -d "$VMDIR/$1" || die "unmount_dirs: $VMDIR/$1 is not a directory"

    # mtab does not list mounts that are the result of an rbind, so we use
    # /proc/mounts instead. Use a reverse sort to do depth-first unmount
    # so that the top level of an rbind will be unmounted last

    dirs=`awk '{print $2}' /proc/mounts | grep -- "^$VMDIR/$1" | sort -r`
    if [ -z "$dirs" ]; then return; fi

    sudo umount $dirs
}

list_chroots () {
    (cd "$VMDIR" && find -maxdepth 3 -name proc | sed -e 's,\./\(.*\)/proc$,\1,')
}

remove_chroots () {
    while [ $# -ge 1 ]; do
	unmount_dirs "$1"
	shift
    done
}

find_shell () {
    for shell in "$PREFERRED_SHELL" "$FALLBACK_SHELL"; do
	if [ -x "$VMDIR/$1/$shell" ]; then
	    echo "$shell"
	    return 0
	fi
    done
    die "Could not find a suitable shell for $1"
}

# FIXME: This doesn't work. Maybe because of sudo.
sanitise_environment () {
    if `which getent >/dev/null 2>&1`; then
	HOME=`getent passwd 0 | cut -d: -f6`
    else
	HOME=/root
    fi
    export HOME
}

# Executes a shell in the chroot. Never returns.
# On error a message is printed and the command exits
exec_chroot () {
    if [ `id -u` -eq 0 ]; then
	SUDO=
    else
	SUDO=sudo
    fi

    shell=`find_shell $1`
    sanitise_environment

    exec $SUDO chroot "$VMDIR/$1" $shell
}

case "$1" in
    -l)
    	list_chroots
	exit 0
    ;;
    -r)
    	shift
	remove_chroots "$@"
	exit 0
    ;;
    -m)
	shift
	mount_dirs "$1"
	exit 0
    ;;
    *)
	mount_dirs "$1"
	exec_chroot "$1"
	# not reached
    ;;
esac

#
# Licence
#
#  Redistribution and use in source and binary forms, with or without
#  modification, are permitted provided that the following conditions
#  are met:
#  
#  a. Redistributions of source code must retain the above copyright
#     notice, this list of conditions and the following disclaimer.
#  b. Redistributions in binary form must reproduce the above copyright
#     notice, this list of conditions and the following disclaimer in the
#     documentation and/or other materials provided with the distribution.
#  c. Neither the name of Quest Software, Inc. nor the names of its
#     contributors may be used to endorse or promote products derived from
#     this software without specific prior written permission.
#
#  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
#  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
#  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
#  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
#  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
#  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
#  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
#  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
#  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
#  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
#  POSSIBILITY OF SUCH DAMAGE.
#