enforce user-specified root directory

Remove the -r option, forcing the user to explicitly pass a root
directory. This removes some confusion wherein we set defaults, but
wouldn't allow all the defaults to be accepted.

This also adds some mild documentation to the help output for genfstab
and pacstrap.

arch-chroot.in

@@ -6,7 +6,7 @@ m4_include(common)
 
 usage() {
   cat <<EOF
-usage: ${0##*/} <chroot-dir>
+usage: ${0##*/} chroot-dir
 
 EOF
 }

genfstab.in

@@ -39,14 +39,16 @@ root=/mnt
 
 usage() {
   cat <<EOF
-usage: ${0##*/} [options]
+usage: ${0##*/} root [options]
 
   Options:
     -L             Use labels for source identifiers
     -p             Avoid printing pseudofs mounts
-    -r root        Generate based on 'root' (default: /mnt)
     -U             Use UUIDs for source identifiers
 
+genfstab generates output suitable for addition to an fstab file based on the
+devices mounted under the mountpoint specified by the given root.
+
 EOF
 }
 
@@ -55,7 +57,7 @@ if [[ -z $1 || $1 = @(-h|--help) ]]; then
   exit $(( $# ? 0 : 1 ))
 fi
 
-while getopts ':Lpr:U' flag; do
+while getopts ':LpU' flag; do
   case $flag in
     L)
       bylabel=1
@@ -66,10 +68,6 @@ while getopts ':Lpr:U' flag; do
     p)
       nopseudofs=1
       ;;
-    r)
-      # trim trailing slashes
-      root=${OPTARG%%+(/)}
-      ;;
     :)
       die '%s: option requires an argument -- '\''%s'\' "${0##*/}" "$OPTARG"
       ;;
@@ -80,6 +78,13 @@ while getopts ':Lpr:U' flag; do
 done
 shift $(( OPTIND - 1 ))
 
+(( $# )) || die "No root directory specified"
+root=${1%%+(/)}; shift
+
+if ! mountpoint -q "$root"; then
+  die "$root is not a mountpoint"
+fi
+
 if (( bylabel && byuuid )); then
   die "cannot specify both -U and -L"
 fi

pacstrap.in

@@ -17,12 +17,14 @@ hostcache=0
 
 usage() {
   cat <<EOF
-usage: ${0##*/} [options]
+usage: ${0##*/} [options] root [packages...]
 
   Options:
-    -r root        Install to 'root' (default: /mnt)
-    -d             Allow installation to a non-mountpoint directory
     -c             Use the package cache on the host, rather than the target
+    -d             Allow installation to a non-mountpoint directory
+
+pacstrap installs packages to the specified new root directory. If no packages
+are given, pacstrap defaults to the "base" group.
 
 EOF
 }
@@ -34,14 +36,11 @@ fi
 
 (( EUID == 0 )) || die 'This script must be run with root privileges'
 
-while getopts ':cdr:' flag; do
+while getopts ':cd' flag; do
   case $flag in
     d)
       directory=1
       ;;
-    r)
-      newroot=$OPTARG
-      ;;
     c)
       hostcache=1
       ;;
@@ -55,11 +54,9 @@ while getopts ':cdr:' flag; do
 done
 shift $(( OPTIND - 1 ))
 
-if (( $# )); then
-  pacman_args=("$@")
-else
-  pacman_args=('base' 'base-devel')
-fi
+(( $# )) || die "No root directory specified"
+newroot=$1; shift
+pacman_args=("${@:-base}")
 
 if (( ! hostcache )); then
   pacman_args+=(--cachedir="$newroot/var/cache/pacman/pkg")