Implement a hook-system that allows to add custom code to the initscripts at certain places

A function add_hook can be called from functions.d to register a hook function. The existing hooks
are based on suggestions from Michael Towers (larch) and on the implementation of initscripts-extras-fbsplash
which currently uses the strings passed to stat_busy and stat_done for this. More hooks can
be added if requested.

The implementation uses associative arrays and will thus only work with bash 4 or later

1 files changed, 45 insertions, 1 deletions

diff --git a/functions b/functions
index 8745a38..56b78be 100644
--- a/functions
+++ b/functions
@@ -229,8 +229,52 @@ ck_status() {
   fi		
 }
 
+###############################
+# Custom hooks in initscripts #
+###############################
+# Hooks can be used to include custom code in various places in the rc.* scripts
+#
+# Define a hook function in a functions.d file using:
+#  function_name() {
+#    ...
+#  }
+#  add_hook hook_name function_name
+# It's allowed to register several hook functions for the same hook
+#
+# The function takes the filename of the script that launched it as an argument
+#
+# Currently, the following hooks exist:
+# start: at the beginning of rc.{multi,shutdown,single,sysinit}
+# end: at the end of rc.{multi,single,sysinit}
+# udevlaunched: after udev has been launched in rc.sysinit and rc.single
+# udevsettled: after uevents have settled in rc.sysinit and rc.single
+# premount: before local filesystems are mounted, but after root is mounted read-write in rc.sysinit
+# prekillall: before all processes are being killed in rc.shutdown and rc.single
+# postkillall: after all processes have been killed in rc.shutdown and rc.single
+# poweroff: directly before powering off in rc.shutdown
+#
+# Make sure to never override the add_hook and run_hook functions via functions.d
+
+declare -A hook_funcs
+for hook in start end udevlaunched udevsettled premount prekillall postkillall poweroff; do
+	hook_funcs["${hook}"]=""
+done
+
+add_hook() {
+	[ -z "$1" -o -z "$2" ] && return 1
+	hook_funcs["$1"]="${hook_funcs["$1"]} $2"
+}
+
+run_hook() {
+	local func
+
+	[ -z "$1" ] && return 1
+	for func in ${hook_funcs["$1"]}; do
+		${func} "$2"
+	done
+}
 
-#Source additional functions at the end to allow overrides
+# Source additional functions at the end to allow overrides
 for f in /etc/rc.d/functions.d/*; do
   if [ -e $f ]; then
     . $f