topology: add simple topology plugin mechanism

Add a simple plugin interface for processing the topology tree. There
can be cases where parts of the topology need to be translated from the
original format into something else. For example one could calculate
some kind of filter coefficients from filter parameters or some other
binary interface parameters from plain text topology tokens.

Mechanism is similar as in alsa-plugins and in the plugin there should
be only 1 function exported of the form:

int _snd_topology_##pluginname##_process (snd_config_t *input, snd_config_t *output)

Input and output parameters are snd_config tree before and after topology2
pre-processing. So the plugin can modify both if needed. There are cases
where the plugin may need to get information from input tree, but make
modifications to the output.

The plugins to be used can be defined in command line with:

alsatplg -DPREPROCESS_PLUGINS="foobar" -c topology.conf -p -o topology.tplg

Multiple plugins should be separated by ":".

Plugins to be used can also be defined with "Define" clause inside the
topology file (but command line takes precedence):

Define {
       PREPROCESS_PLUGINS "foobar"
}

Link: https://github.com/alsa-project/alsa-utils/pull/129
Signed-off-by: Jaska Uimonen <jaska.uimonen@linux.intel.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

topology/pre-process-external.h

@@ -0,0 +1,39 @@
+/*
+ *   This library is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU Lesser General Public License as
+ *   published by the Free Software Foundation; either version 2.1 of
+ *   the License, or (at your option) any later version.
+ *
+ *   This program 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 Lesser General Public License for more details.
+ *
+ *   You should have received a copy of the GNU Lesser General Public
+ *   License along with this library; if not, write to the Free Software
+ *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+#ifndef __PRE_PROCESS_EXTERNAL_H
+#define __PRE_PROCESS_EXTERNAL_H
+
+#define PROCESS_FUNC_PREFIX "_snd_topology_"
+#define PROCESS_FUNC_POSTFIX "_process"
+#define PROCESS_LIB_PREFIX "libalsatplg_module_"
+#define PROCESS_LIB_POSTFIX ".so"
+
+/**
+ * Define the object entry for external pre-process plugins
+ */
+#define SND_TOPOLOGY_PLUGIN_ENTRY(name) _snd_topology_##name##_process
+
+/**
+ * Define the plugin
+ */
+#define SND_TOPOLOGY_PLUGIN_DEFINE_FUNC(plugin) \
+	__attribute__ ((visibility ("default"))) \
+	int SND_TOPOLOGY_PLUGIN_ENTRY(plugin) (snd_config_t *input, snd_config_t *output)
+
+typedef int (*plugin_pre_process)(snd_config_t *input, snd_config_t *output);
+
+#endif /* __PRE_PROCESS_EXTERNAL_H */

topology/pre-processor.c

@@ -25,11 +25,126 @@
 #include <string.h>
 #include <errno.h>
 #include <regex.h>
+#include <dlfcn.h>
 
 #include <alsa/asoundlib.h>
 #include "gettext.h"
 #include "topology.h"
 #include "pre-processor.h"
+#include "pre-process-external.h"
+
+#define SND_TOPOLOGY_MAX_PLUGINS 32
+
+static int get_plugin_string(struct tplg_pre_processor *tplg_pp, const char *pre_processor_defs,
+			     char **plugin_string)
+{
+	const char *lib_names_t = NULL;
+	snd_config_t *defines;
+	int ret;
+
+	ret = snd_config_search(tplg_pp->input_cfg, "Define.PREPROCESS_PLUGINS", &defines);
+	if (ret < 0)
+		return ret;
+
+	ret = snd_config_get_string(defines, &lib_names_t);
+	if (ret < 0)
+		return ret;
+
+	*plugin_string = strdup(lib_names_t);
+
+	if (!*plugin_string)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static int run_plugin(struct tplg_pre_processor *tplg_pp, char *plugin)
+{
+	plugin_pre_process process;
+	char *xlib, *xfunc, *path;
+	void *h = NULL;
+	int ret = 0;
+
+	/* compose the plugin path, if not from environment, then from default plugins dir */
+	path = getenv("ALSA_TOPOLOGY_PLUGIN_DIR");
+	if (!path)
+		path = ALSA_TOPOLOGY_PLUGIN_DIR;
+
+	xlib = tplg_snprintf("%s/%s%s%s", path, PROCESS_LIB_PREFIX, plugin,
+			     PROCESS_LIB_POSTFIX);
+	xfunc = tplg_snprintf("%s%s%s", PROCESS_FUNC_PREFIX, plugin,
+			      PROCESS_FUNC_POSTFIX);
+
+	if (!xlib || !xfunc) {
+		fprintf(stderr, "can't reserve memory for plugin paths and func names\n");
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	/* open plugin */
+	h = dlopen(xlib, RTLD_NOW);
+	if (!h) {
+		fprintf(stderr, "unable to open library '%s'\n", xlib);
+		ret = -EINVAL;
+		goto err;
+	}
+
+	/* find function */
+	process = dlsym(h, xfunc);
+
+	if (!process) {
+		fprintf(stderr, "symbol 'topology_process' was not found in %s\n", xlib);
+		ret = -EINVAL;
+		goto err;
+	}
+
+	/* process plugin */
+	process(tplg_pp->input_cfg, tplg_pp->output_cfg);
+
+err:
+	if (h)
+		dlclose(h);
+	if (xlib)
+		free(xlib);
+	if (xfunc)
+		free(xfunc);
+
+	return ret;
+}
+
+static int pre_process_plugins(struct tplg_pre_processor *tplg_pp, const char *pre_processor_defs)
+{
+	char *plugins[SND_TOPOLOGY_MAX_PLUGINS];
+	char *plugin_string;
+	int count;
+	int ret;
+	int i;
+
+	/* parse plugin names */
+	ret = get_plugin_string(tplg_pp, pre_processor_defs, &plugin_string);
+
+	/* no plugins defined, so just return */
+	if (ret < 0)
+		return 0;
+
+	count = 0;
+	plugins[count] = strtok(plugin_string, ":");
+	while ((count < SND_TOPOLOGY_MAX_PLUGINS - 1) && plugins[count]) {
+		count++;
+		plugins[count] = strtok(NULL, ":");
+	}
+
+	/* run all plugins */
+	for (i = 0; i < count; i++) {
+		ret = run_plugin(tplg_pp, plugins[i]);
+		if (ret < 0)
+			return ret;
+	}
+
+	free(plugin_string);
+
+	return 0;
+}
 
 /*
  * Helper function to find config by id.
@@ -572,6 +687,13 @@ int pre_process(struct tplg_pre_processor *tplg_pp, char *config, size_t config_
 		goto err;
 	}
 
+	/* process topology plugins */
+	err = pre_process_plugins(tplg_pp, pre_processor_defs);
+	if (err < 0) {
+		fprintf(stderr, "Unable to run pre-process plugins\n");
+		goto err;
+	}
+
 	/* save config to output */
 	err = snd_config_save(tplg_pp->output_cfg, tplg_pp->output);
 	if (err < 0)

topology/pre-processor.h

@@ -26,6 +26,7 @@
 #define ARRAY_SIZE(a) (sizeof (a) / sizeof (a)[0])
 
 #define MAX_CONFIGS_IN_TEMPLATE	32
+
 struct config_template_items {
 	char *int_config_ids[MAX_CONFIGS_IN_TEMPLATE];
 	char *string_config_ids[MAX_CONFIGS_IN_TEMPLATE];