add_resolve_conf: recursive host + target symlinks

arch-chroot.in

@@ -27,32 +27,51 @@ itself to make it a mountpoint, i.e. 'mount --bind /your/chroot /your/chroot'.
 EOF
 }
 
+resolve_link() {
+  local target=$1
+  local root=$2
+
+  # If a root was given, make sure it ends in a slash.
+  [[ -n $root && $root != */ ]] && root=$root/
+
+  while [[ -L $target ]]; do
+    target=$(readlink -m "$target")
+    # If a root was given, make sure the target is under it.
+    # Make sure to strip any leading slash from target first.
+    [[ -n $root && $target != $root* ]] && target=$root${target#/}
+  done
+
+  printf %s "$target"
+}
+
 chroot_add_resolv_conf() {
-  local chrootdir=$1 resolv_conf=$1/etc/resolv.conf
+  local chrootdir=$1
+  local src=$(resolve_link /etc/resolv.conf)
+  local dest=$(resolve_link "$chrootdir/etc/resolv.conf" "$chrootdir")
 
-  [[ -e /etc/resolv.conf ]] || return 0
+  # If we don't have a source resolv.conf file, there's nothing useful we can do.
+  [[ -e $src ]] || return 0
 
-  # Handle resolv.conf as a symlink to somewhere else.
-  if [[ -L $chrootdir/etc/resolv.conf ]]; then
-    # readlink(1) should always give us *something* since we know at this point
-    # it's a symlink. For simplicity, ignore the case of nested symlinks.
-    resolv_conf=$(readlink "$chrootdir/etc/resolv.conf")
-    if [[ $resolv_conf = /* ]]; then
-      resolv_conf=$chrootdir$resolv_conf
-    else
-      resolv_conf=$chrootdir/etc/$resolv_conf
-    fi
+  if [[ ! -e $dest ]]; then
+    # There are two reasons the destination might not exist:
+    #
+    #   1. There may be no resolv.conf in the chroot.  In this case, $dest won't exist,
+    #      and it will be equal to $1/etc/resolv.conf.  In this case, we'll just exit.
+    #      The chroot environment must not be concerned with DNS resolution.
+    #
+    #   2. $1/etc/resolv.conf is (or resolves to) a broken link.  The environment
+    #      clearly intends to handle DNS resolution, but something's wrong.  Maybe it
+    #      normally creates the target at boot time.  We'll (try to) take care of it by
+    #      creating a dummy file at the target, so that we have something to bind to.
 
-    # ensure file exists to bind mount over
-    if [[ ! -f $resolv_conf ]]; then
-      install -Dm644 /dev/null "$resolv_conf" || return 1
-    fi
-  elif [[ ! -e $chrootdir/etc/resolv.conf ]]; then
-    # The chroot might not have a resolv.conf.
-    return 0
+    # Case 1.
+    [[ $dest = $chrootdir/etc/resolv.conf ]] && return 0
+
+    # Case 2.
+    install -Dm644 /dev/null "$dest" || return 1
   fi
 
-  chroot_add_mount /etc/resolv.conf "$resolv_conf" --bind
+  chroot_add_mount "$src" "$dest" --bind
 }
 
 while getopts ':hNu:' flag; do