pam_motd: Support multiple motd paths specified, with filename overrides (#69)

Adds specifying multiple paths to motd files and motd.d
directories to be displayed. A colon-separated list of
paths is specified as arguments motd and motd_dir to the
pam_motd module.

This gives packages several options to install motd files to.
By default, the paths are, with highest priority first:
/etc/motd
/run/motd
/usr/lib/motd
/etc/motd.d/
/run/motd.d/
/usr/lib/motd.d/

Which is equivalent to the following arguments:
motd=/etc/motd:/run/motd:/usr/lib/motd
motd_dir=/etc/motd.d:/run/motd.d:/usr/lib/motd.d

Files with the same filename in a lower-priority directory,
as specified by the order in the colon-separated list, are
overridden, meaning PAM will not display them.

This allows a package to contain motd files under
/usr/lib instead of the host configuration in /etc.
A service may also write a dynamically generated motd in
/run/motd.d/ and have PAM display it without needing a
symlink from /etc/motd.d/ installed.

Closes #68

* modules/pam_motd/pam_motd.8.xml: update documentation
* modules/pam_motd/pam_motd.c: add specifying multiple motd paths
* xtests/.gitignore: add generated test script
* xtests/Makefile.am: add test source, scripts and config files
* xtests/tst-pam_motd.c: create
* xtests/tst-pam_motd.sh: create
* xtests/tst-pam_motd1.pamd: create
* xtests/tst-pam_motd1.sh: create
* xtests/tst-pam_motd2.pamd: create
* xtests/tst-pam_motd2.sh: create
* xtests/tst-pam_motd3.pamd: create
* xtests/tst-pam_motd3.sh: create

1 files changed, 36 insertions, 0 deletions

diff --git a/xtests/tst-pam_motd1.sh b/xtests/tst-pam_motd1.sh
new file mode 100755
index 00000000..cc888547
--- /dev/null
+++ b/xtests/tst-pam_motd1.sh
@@ -0,0 +1,36 @@
+#!/bin/bash
+
+TST_DIR="tst-pam_motd1.d"
+
+function tst_cleanup() {
+    rm -rf "${TST_DIR}"
+    rm -f tst-pam_motd1.out
+}
+
+mkdir -p ${TST_DIR}
+mkdir -p ${TST_DIR}/etc/motd.d
+
+# Verify the case of single motd and motd.d directory works
+echo "motd: /etc/motd" > ${TST_DIR}/etc/motd
+echo "motd: /etc/motd.d/test" > ${TST_DIR}/etc/motd.d/test
+
+./tst-pam_motd tst-pam_motd1 > tst-pam_motd1.out
+
+RET=$?
+
+motd_to_show_output=$(cat tst-pam_motd1.out | grep "motd: /etc/motd")
+if [ -z "${motd_to_show_output}" ];
+then
+    tst_cleanup
+    exit 1
+fi
+
+motd_dir_to_show_output=$(cat tst-pam_motd1.out | grep "motd: /etc/motd.d/test")
+if [ -z "${motd_dir_to_show_output}" ];
+then
+    tst_cleanup
+    exit 1
+fi
+
+tst_cleanup
+exit $RET