systemd: support disabling cloud-init via file or kernel cmdline

This adds a systemd generator for a 'cloud-init.target'.  That target will
be WantedBy multi-user.target in the default case.  If there is a file
/etc/cloud/cloud-init.disabled or the kernel command line contains
'cloud-init=disabled' then cloud-init will not affect boot at all.

There are some packages/debian changes to affect this:
 * postinst, preinst: these are necessary to remove some
   old target files for multi-user.target (LP: #1552999)
 * changes to include these files in the debian source package.
 * rules.in: supports DEB_BUILD_OPTIONS=nocheck to not run check

setup.py: mostly changes to support installing the generator
          but also pep8 fixes along the way

systemd/*: make each of the services 'WantedBy=cloud-init.target'
           rather than being wanted by multi-user.target

1 files changed, 128 insertions, 0 deletions

diff --git a/systemd/cloud-init-generator b/systemd/cloud-init-generator
new file mode 100755
index 00000000..9d1e22f0
--- /dev/null
+++ b/systemd/cloud-init-generator
@@ -0,0 +1,128 @@
+#!/bin/sh
+set -f
+
+LOG=""
+DEBUG_LEVEL=1
+LOG_D="/run"
+ENABLE="enabled"
+DISABLE="disabled"
+CLOUD_SYSTEM_TARGET="/lib/systemd/system/cloud-init.target"
+CLOUD_TARGET_NAME="cloud-init.target"
+# lxc sets 'container', but lets make that explicitly a global
+CONTAINER="${container}"
+
+debug() {
+    local lvl="$1"
+    shift
+    [ "$lvl" -gt "$DEBUG_LEVEL" ] && return
+    if [ -z "$LOG" ]; then
+        local log="$LOG_D/${0##*/}.log"
+        { : > "$log"; } >/dev/null 2>&1 && LOG="$log" ||
+            LOG="/dev/kmsg"
+    fi
+    echo "$@" >> "$LOG"
+}
+
+etc_file() {
+    local pprefix="${1:-/etc/cloud/cloud-init.}"
+    _RET="unset"
+    [ -f "${pprefix}$ENABLE" ] && _RET="$ENABLE" && return 0
+    [ -f "${pprefix}$DISABLE" ] && _RET="$DISABLE" && return 0
+    return 0
+}
+
+read_proc_cmdline() {
+    if [ "$CONTAINER" = "lxc" ]; then
+        _RET_MSG="ignored: \$container=$CONTAINER"
+        _RET=""
+        return 0
+    fi
+
+    if systemd-detect-virt --container --quiet; then
+        _RET_MSG="ignored: detect-virt is container"
+        _RET=""
+        return 0
+    fi
+
+    _RET_MSG="/proc/cmdline"
+    read _RET < /proc/cmdline
+}
+
+kernel_cmdline() {
+    local cmdline="" tok=""
+    if [ -n "${KERNEL_CMDLINE+x}" ]; then
+        # use KERNEL_CMDLINE if present in environment even if empty
+        cmdline=${KERNEL_CMDLINE}
+        debug 1 "kernel command line from env KERNEL_CMDLINE: $cmdline"
+    elif read_proc_cmdline; then
+        read_proc_cmdline && cmdline="$_RET"
+        debug 1 "kernel command line ($_RET_MSG): $cmdline"
+    fi
+    _RET="unset"
+    cmdline=" $cmdline "
+    tok=${cmdline##* cloud-init=}
+    [ "$tok" = "$cmdline" ] && _RET="unset"
+    tok=${tok%% *}
+    [ "$tok" = "$ENABLE" -o "$tok" = "$DISABLE" ] && _RET="$tok"
+    return 0
+}
+
+default() {
+    _RET="$ENABLE"
+}
+
+main() {
+    local normal_d="$1" early_d="$2" late_d="$3"
+    local target_name="multi-user.target" gen_d="$early_d"
+    local link_path="$gen_d/${target_name}.wants/${CLOUD_TARGET_NAME}"
+
+    debug 1 "$0 normal=$normal_d early=$early_d late=$late_d"
+    debug 2 "$0 $*"
+
+    local search result="error" ret=""
+    for search in kernel_cmdline etc_file default; do
+        if $search; then
+            debug 1 "$search found $_RET"
+            [ "$_RET" = "$ENABLE" -o "$_RET" = "$DISABLE" ] &&
+                result=$_RET && break
+        else
+            ret=$?
+            debug 0 "search $search returned $ret"
+        fi
+    done
+    
+    if [ "$result" = "$ENABLE" ]; then
+        if [ -e "$link_path" ]; then
+                debug 1 "already enabled: no change needed"
+        else
+            [ -d "${link_path%/*}" ] || mkdir -p "${link_path%/*}" ||
+                debug 0 "failed to make dir $link_path"
+            if ln -snf "$CLOUD_SYSTEM_TARGET" "$link_path"; then
+                debug 1 "enabled via $link_path -> $CLOUD_SYSTEM_TARGET"
+            else
+                ret=$?
+                debug 0 "[$ret] enable failed:" \
+                    "ln $CLOUD_SYSTEM_TARGET $link_path"
+            fi
+        fi
+    elif [ "$result" = "$DISABLE" ]; then
+        if [ -f "$link_path" ]; then
+            if rm -f "$link_path"; then
+                debug 1 "disabled. removed existing $link_path"
+            else
+                ret=$?
+                debug 0 "[$ret] disable failed, remove $link_path"
+            fi
+        else
+            debug 1 "already disabled: no change needed [no $link_path]"
+        fi
+    else
+        debug 0 "unexpected result '$result'"
+        ret=3
+    fi
+    return $ret
+}
+
+main "$@"
+
+# vi: ts=4 expandtab