main: Add (mcron main) module.

Remove 'ed' hack to eval content of scm/mcron/main.scm in the C wrapper.
Use proper libguile functions instead.

* scm/mcron/main.scm (mcron main): New module.
(show-version, show-package-information, show-help, main): Remove
extra newline characters in strings.
* mcron.c.template: Rename to ...
* mcron.c: ... this.
(inner_main): Set current module to (mcron main).
* makefile.ed: Delete file.
* configure.ac: Remove check for 'ed'.
* makefile.am: Adjust accordingly.
* .gitignore: Likewise.

mcron.c

@@ -0,0 +1,102 @@
+/* mcron - run jobs at scheduled times
+
+   Copyright (C) 2015, 2016 Mathieu Lirzin
+   Copyright (C) 2003, 2014 Dale Mellor
+
+   This file is part of GNU Mcron.
+
+   GNU Mcron is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   GNU Mcron is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with GNU Mcron.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* This C code represents the thinnest possible wrapper around the Guile code
+   which constitutes all the functionality of the mcron program.  There are
+   two plus one reasons why we need to do this, and one very unfortunate
+   consequence.
+
+   * Firstly, SUID does not work on an executable script.  In the end, it is
+     the execution of the translator, in our case guile, which determines the
+     effective user, and it is not wise to make the system guile installation
+     SUID root!
+
+   * Secondly, executable scripts show up in ugly ways in listings of the
+     system process table.  Guile in particular, with its multi-line
+     #! ...\ \n -s ...!#
+     idiosyncracies shows up in process listings in a way that is difficult
+     to determine what program is actually running.
+
+   * A third reason for the C wrapper which might be mentioned is that a
+     security-conscious system administrator can choose to only install a
+     binary, thus removing the possibility of a user studying a guile script
+     and working out ways of hacking it to his own ends, or worse still
+     finding a way to modify it to his own ends.
+
+   * Unfortunately, running the guile script from inside a C program means
+     that the sigaction function does not work.  Instead, it is necessary to
+     perform the signal processing in C.  */
+
+#include <libguile.h>
+#include <signal.h>
+#include <string.h>
+
+/* This is a function designed to be installed as a signal handler, for
+   signals which are supposed to initiate shutdown of this program.  It calls
+   the scheme procedure (see mcron.scm for details) to do all the work, and
+   then exits.  */
+
+void
+react_to_terminal_signal (int sig)
+{
+  scm_c_eval_string ("(delete-run-file)");
+  exit (1);
+}
+
+/* This is a function designed to be callable from scheme, and sets up all the
+   signal handlers required by the cron personality.  */
+
+SCM
+set_cron_signals ()
+{
+  static struct sigaction sa;
+
+  memset (&sa, 0, sizeof (sa));
+  sa.sa_handler = react_to_terminal_signal;
+  sigaction (SIGTERM, &sa, 0);
+  sigaction (SIGINT,  &sa, 0);
+  sigaction (SIGQUIT, &sa, 0);
+  sigaction (SIGHUP,  &sa, 0);
+
+  return SCM_BOOL_T;
+}
+
+/* The effective main function (i.e. the one that actually does some work).
+   We register the function above with the guile system, and then execute the
+   mcron guile program.  */
+
+void
+inner_main (void *closure, int argc, char **argv)
+{
+  scm_set_current_module (scm_c_resolve_module ("mcron main"));
+  scm_c_define_gsubr ("c-set-cron-signals", 0, 0, 0, set_cron_signals);
+  scm_c_eval_string ("(main)");
+}
+
+/* The real main function.  Does nothing but start up the guile subsystem. */
+
+int
+main (int argc, char **argv)
+{
+  setenv ("GUILE_LOAD_PATH", GUILE_LOAD_PATH, 1);
+  scm_boot_guile (argc, argv, inner_main, 0);
+
+  return 0;
+}