ndctl: check the old directory for monitor.conf

Scripts may still reference / install the monitor.conf file
in the old path.  Check there first to avoid breaking backwards
compatibility.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>

Related: RHEL-10382
diff --git a/config.h.meson b/config.h.meson
index 5441dff..32e7941 100644
--- a/config.h.meson
+++ b/config.h.meson
@@ -149,6 +149,7 @@
 /* Locations to install configuration files, key config, man pages, etc.. */
 #mesondefine NDCTL_CONF_FILE
 #mesondefine NDCTL_CONF_DIR
+#mesondefine LEGACY_CONF_FILE
 #mesondefine DAXCTL_CONF_DIR
 #mesondefine NDCTL_KEYS_DIR
 #mesondefine NDCTL_MAN_PATH
diff --git a/meson.build b/meson.build
index 2cb188f..96bc386 100644
--- a/meson.build
+++ b/meson.build
@@ -259,8 +259,11 @@ conf.set10('HAVE_JSON_U64',
 
 ndctlconf_dir = sysconfdir / 'ndctl.conf.d'
 ndctlconf = ndctlconf_dir / 'monitor.conf'
+legacyconf_dir = sysconfdir / 'ndctl'
+legacyconf = legacyconf_dir / 'monitor.conf'
 conf.set_quoted('NDCTL_CONF_FILE', ndctlconf)
 conf.set_quoted('NDCTL_CONF_DIR', ndctlconf_dir)
+conf.set_quoted('LEGACY_CONF_FILE', legacyconf)
 
 ndctlkeys_dir = sysconfdir / 'ndctl' / 'keys'
 conf.set_quoted('NDCTL_KEYS_DIR', ndctlkeys_dir)
diff --git a/ndctl/meson.build b/ndctl/meson.build
index 050d576..dd13a41 100644
--- a/ndctl/meson.build
+++ b/ndctl/meson.build
@@ -59,7 +59,7 @@ endif
 if get_option('systemd').enabled()
   install_data('ndctl-monitor.service', install_dir : systemdunitdir)
 endif
-install_data('monitor.conf', install_dir : ndctlconf_dir)
+install_data('monitor.conf', install_dir : legacyconf_dir)
 install_data('ndctl.conf', install_dir : ndctlconf_dir)
 install_data('keys.readme', install_dir : ndctlkeys_dir)
 
diff --git a/ndctl/monitor.c b/ndctl/monitor.c
index bd8a748..07da7f5 100644
--- a/ndctl/monitor.c
+++ b/ndctl/monitor.c
@@ -591,6 +591,15 @@ int cmd_monitor(int argc, const char **argv, struct ndctl_ctx *ctx)
 	else
 		monitor.ctx.log_priority = LOG_INFO;
 
+	/*
+	 * First, check the legacy path to see if a monitor.conf
+	 * file exists there.  If so, add a [monitor] header
+	 * and use its contents.
+	 */
+	if (!monitor.configs && (stat(LEGACY_CONF_FILE, &st) == 0) &&
+	    S_ISREG(st.st_mode))
+		monitor.configs = LEGACY_CONF_FILE;
+
 	ndctl_configs = ndctl_get_config_path(ctx);
 	if (!monitor.configs && ndctl_configs) {
 		rc = asprintf(&path, "%s/monitor.conf", ndctl_configs);