[type/__package_opkg] Fix explorer running in parallel

cdist/conf/type/__package_opkg/explorer/pkg_status

@@ -1,7 +1,8 @@
-#!/bin/sh
+#!/bin/sh -e
 #
 # 2011 Nico Schottelius (nico-cdist at schottelius.org)
 # 2012 Giel van Schijndel (giel plus cdist at mortis dot eu)
+# 2020 Dennis Camera (dennis.camera at ssrq-sds-fds.ch)
 #
 # This file is part of cdist.
 #
@@ -19,21 +20,51 @@
 # along with cdist. If not, see <http://www.gnu.org/licenses/>.
 #
 #
-# Retrieve the status of a package - parsed opkg output
+# Retrieve the status of a package - parses opkg output
 #
 
-if [ -f "$__object/parameter/name" ]; then
-   name="$(cat "$__object/parameter/name")"
+LOCKFILE="${__type_explorer}/cdist_opkg.lock"
+_lock() (
+	set -o noclobber
+	until echo $$>"${LOCKFILE}"
+	do
+		while test -f "${LOCKFILE}"; do sleep 1; done
+	done
+
+) 2>/dev/null
+_unlock() {
+	if test -s "${LOCKFILE}" && test "$(cat "${LOCKFILE}")" = $$
+	then
+		rm "${LOCKFILE}"
+	fi
+}
+
+
+if test -f "${__object}/parameter/name"
+then
+	pkg_name=$(cat "${__object}/parameter/name")
 else
-   name="$__object_id"
+	pkg_name=$__object_id
 fi
 
-# Except dpkg failing, if package is not known / installed
-if opkg status "$name" 2>/dev/null | grep -q "^Status: install user installed$"; then
-   echo "present"
-   exit 0
-elif [ "$(opkg info "$name" 2> /dev/null | wc -l)" -eq 0 ]; then
-   echo "absent notpresent"
-   exit 0
+
+# NOTE: We need to lock parallel execution of this explorer because opkg will
+# try to acquire the OPKG lock (usually /var/lock/opkg.lock) using lockf(2) for
+# every operation. It will not wait for the lock but terminate with an error.
+# This leads to incorrect 'absent notpresent' statuses when parallel execution
+# is enabled.
+trap _unlock EXIT
+_lock
+
+
+# Except opkg failing, if package is not known / installed
+if opkg status "${pkg_name}" 2>/dev/null \
+	| grep -q -e '^Status: [^ ][^ ]* [^ ][^ ]* installed$'
+then
+	echo 'present'
+elif opkg info "${pkg_name}" 2>/dev/null | grep -q .
+then
+	echo 'absent notpresent'
+else
+	echo 'absent'
 fi
-echo "absent"