conf: look in conf.d directories and merge all sections

Load all sections found in all prefix/name.conf.d directories and add
them to the config as overrides.
If for example jack.conf is loaded, check in:

  /usr/share/pipewire/jack.conf.d/
  /etc/pipewire/jack.conf.d/
  $XDG_CONFIG_HOME/pipewire/jack.conf.d/
     or ~/.config/pipewire/jack.conf.d/

For .conf files and also process the sections. The files are processed
in sorted order so 10-remap.conf can be used to specify the order.

When processing a section, first the global conf is applied and then the
overrides in their order.

This makes it possible to override properties or add modules,
objects and custom matching rules.

Since the merging logic is handled either internally or by the
application, we can add more syntax later to do more complex merges.

See #207

src/pipewire/conf.c

@@ -33,6 +33,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 #include <sys/wait.h>
+#include <dirent.h>
 #if HAVE_PWD_H
 #include <pwd.h>
 #endif
@@ -174,6 +175,47 @@ no_config:
 	return 0;
 }
 
+static int get_config_dir(char *path, size_t size, const char *prefix, const char *name, int *level)
+{
+	int res;
+
+	if (prefix == NULL) {
+		prefix = name;
+		name = NULL;
+	}
+	if ((res = get_abs_path(path, size, prefix, name)) != 0) {
+		if ((*level)++ == 0)
+			return res;
+		return -ENOENT;
+	}
+
+	if ((res = get_envconf_path(path, size, prefix, name)) != 0) {
+		if ((*level)++ == 0)
+			return res;
+		return -ENOENT;
+	}
+
+	if (*level == 0) {
+		(*level)++;
+		if ((res = get_confdata_path(path, size, prefix, name)) != 0)
+			return res;
+	}
+	if (pw_check_option("no-config", "true"))
+		return 0;
+
+	if (*level == 1) {
+		(*level)++;
+		if ((res = get_configdir_path(path, size, prefix, name)) != 0)
+			return res;
+	}
+	if (*level == 2) {
+		(*level)++;
+		if ((res = get_homeconf_path(path, size, prefix, name)) != 0)
+			return res;
+	}
+	return 0;
+}
+
 static int get_envstate_path(char *path, size_t size, const char *prefix, const char *name)
 {
 	const char *dir;
@@ -380,10 +422,32 @@ error:
 	return -errno;
 }
 
+static void add_override(struct pw_properties *conf, struct pw_properties *override,
+		const char *path, int level, int index)
+{
+	const struct spa_dict_item *it;
+	char key[1024];
+	snprintf(key, sizeof(key), "override.%d.%d.config.path", level, index);
+	pw_properties_set(conf, key, path);
+	spa_dict_for_each(it, &override->dict) {
+		snprintf(key, sizeof(key), "override.%d.%d.%s", level, index, it->key);
+		pw_properties_set(conf, key, it->value);
+	}
+}
+
+static int conf_filter(const struct dirent *entry)
+{
+	return spa_strendswith(entry->d_name, ".conf");
+}
+
 SPA_EXPORT
 int pw_conf_load_conf(const char *prefix, const char *name, struct pw_properties *conf)
 {
 	char path[PATH_MAX];
+	char fname[PATH_MAX + 256];
+	int i, res, level = 0;
+	struct pw_properties *override = NULL;
+	const char *dname;
 
 	if (name == NULL) {
 		pw_log_debug("%p: config name must not be NULL", conf);
@@ -394,11 +458,45 @@ int pw_conf_load_conf(const char *prefix, const char *name, struct pw_properties
 		pw_log_debug("%p: can't load config '%s': %m", conf, path);
 		return -ENOENT;
 	}
-	pw_properties_set(conf, "config.path", path);
 	pw_properties_set(conf, "config.prefix", prefix);
 	pw_properties_set(conf, "config.name", name);
+	pw_properties_set(conf, "config.path", path);
 
-	return conf_load(path, conf);
+	if ((res = conf_load(path, conf)) < 0)
+		return res;
+
+	pw_properties_setf(conf, "config.name.d", "%s.d", name);
+	dname = pw_properties_get(conf, "config.name.d");
+
+	while (true) {
+		struct dirent **entries = NULL;
+		int n;
+
+		if (get_config_dir(path, sizeof(path), prefix, dname, &level) <= 0)
+			break;
+
+		n = scandir(path, &entries, conf_filter, alphasort);
+		if (n == 0)
+			continue;
+		if (n < 0) {
+			pw_log_warn("scandir %s failed: %m", path);
+			continue;
+		}
+		if (override == NULL &&
+		    (override = pw_properties_new(NULL, NULL)) == NULL)
+			return -errno;
+
+		for (i = 0; i < n; i++) {
+			snprintf(fname, sizeof(fname), "%s/%s", path, entries[i]->d_name);
+			if (conf_load(fname, override) >= 0)
+				add_override(conf, override, fname, level, i);
+			pw_properties_clear(override);
+			free(entries[i]);
+		}
+		free(entries);
+	}
+	pw_properties_free(override);
+	return 0;
 }
 
 SPA_EXPORT
@@ -719,15 +817,27 @@ int pw_context_conf_section_for_each(struct pw_context *context, const char *sec
 		void *data)
 {
 	struct pw_properties *conf = context->conf;
-	const char *str, *path;
+	const char *path = NULL;
+	const struct spa_dict_item *it;
 	int res;
 
-	if ((str = pw_properties_get(conf, section)) == NULL)
-		return 0;
+	spa_dict_for_each(it, &conf->dict) {
+		if (spa_strendswith(it->key, "config.path")) {
+			path = it->value;
+			continue;
 
-	path = pw_properties_get(conf, "config.path");
-	pw_log_info("handle config '%s' section '%s'", path, section);
-	res = callback(data, path, section, str, strlen(str));
+		} else if (spa_streq(it->key, section)) {
+			pw_log_info("handle config '%s' section '%s'", path, section);
+		} else if (spa_strstartswith(it->key, "override.") &&
+		    spa_strendswith(it->key, section)) {
+			pw_log_info("handle override '%s' section '%s'", path, section);
+		} else
+			continue;
+
+		res = callback(data, path, section, it->value, strlen(it->value));
+		if (res != 0)
+			break;
+	}
 	return res;
 }