[fprint] [PATCH 1/8] lib: Add support for dynamically loading drivers.

[Kunal Gangakhedkar]

It's very unlikely that people have more than one fingerprint reader
on their computers and being actively used.

The current design of fprint library loads all the drivers as built-ins.

On systems with smaller memory (such as embedded systems), a few KBs are
also important.

This commit adds basic API for loading/unloading modules.
Right now, only the drivers are treated as loadable modules.

The implementation is just a wrapper around dlopen()/dlsym() API.

The design derives from the linux kernel's implementation of loadable
modules.

Signed-off-by: Kunal Gangakhedkar <kunal.gangakhedkar at gmail.com>
---
 libfprint/module.c |  148 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 libfprint/module.h |   57 ++++++++++++++++++++
 2 files changed, 205 insertions(+)
 create mode 100644 libfprint/module.c
 create mode 100644 libfprint/module.h

diff --git a/libfprint/module.c b/libfprint/module.c
new file mode 100644
index 0000000..05368af
--- /dev/null
+++ b/libfprint/module.c
@@ -0,0 +1,148 @@
+/*
+ * Support for dynamically loading drivers
+ * Copyright (C) 2012 Kunal Gangakhedkar <kunal.gangakhedkar at gmail.com>
+ *
+ * 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 library 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
+ */
+
+#include <errno.h>
+#include <string.h>
+#include <dlfcn.h>
+
+#include <glib.h>
+#include <config.h>
+#include <fp_internal.h>
+
+#include "module.h"
+
+static GSList *modules = NULL;
+
+static int module_exists(const char *mod_path, GSList **entry);
+
+API_EXPORTED int load_module(const char *mod_path)
+{
+	int rc = 0;
+	initcall_t init_call = NULL;
+	exitcall_t exit_call = NULL;
+	struct fp_mod *mod = NULL;
+	void *handle = NULL;
+
+	if (module_exists(mod_path, NULL)) {
+		fp_info("Module '%s' already loaded - skipping..\n", mod_path);
+		return rc;
+	}
+
+	handle = dlopen(mod_path, RTLD_LAZY);
+	if (!handle) {
+		fp_err("failed to load module %s\n", dlerror());
+		return errno;
+	}
+
+	init_call = (initcall_t)dlsym(handle, "init_mod");
+	if (!init_call) {
+		fp_err("failed to get init call pointer: %s\n", dlerror());
+		rc = errno;
+		goto close_lib;
+	}
+
+	exit_call = (exitcall_t)dlsym(handle, "cleanup_mod");
+
+	mod = g_malloc0(sizeof(*mod));
+	mod->init = init_call;
+	mod->exit = exit_call;
+	mod->handle = handle;
+	strncpy(mod->path, mod_path, MODULE_PATH_LEN);
+
+	/*
+	 * TODO:
+	 * For now, copy the file path into name.
+	 * When we add support for MODULE_NAME(), we need to change this
+	 * to copy the actual module name.
+	 */
+	strncpy(mod->name, mod_path, MODULE_NAME_LEN);
+
+	rc = init_call();
+	if (rc < 0) {
+		/* Init routine failed. Abort loading of module.. */
+		fp_warn("module '%s' returned %d - aborting loading", mod->name, rc);
+		g_free(mod);
+	} else {
+		modules = g_slist_prepend(modules, (gpointer) mod);
+	}
+	goto out;
+
+close_lib:
+	dlclose(handle);
+out:
+	return rc;
+}
+
+API_EXPORTED int unload_module(const char *mod_path)
+{
+	GSList *entry = NULL;
+	struct fp_mod *mod = NULL;
+	int rc = 0;
+
+	if (!module_exists(mod_path, &entry)) {
+		fp_err("Module '%s' not found. Perhaps not loaded?\n", mod_path);
+		return -ENOENT;
+	}
+
+	mod = (struct fp_mod*)entry->data;
+
+	modules = g_slist_delete_link(modules, entry);
+
+	if (mod->exit) {
+		mod->exit();
+	}
+
+	rc = dlclose(mod->handle);
+	if (rc < 0) {
+		/*
+		 * This is a potential memory leak.
+		 * The loaded library is dangling here.
+		 * Hopefully, sensible OS will clean it out when the main process
+		 * terminates.
+		 */
+		fp_dbg("Failed to unload module '%s': %s\n", mod->name, dlerror());
+	}
+
+	if (entry)
+		entry = NULL;
+
+	g_free(mod);
+	mod = NULL;
+
+	return rc;
+}
+
+static int module_exists(const char *mod_path, GSList **entry)
+{
+	GSList *elem = modules;
+
+	if (g_slist_length(elem) == 0)
+		return 0;
+
+	do {
+		struct fp_mod *mod = (struct fp_mod*)elem->data;
+		if (strncmp(mod->path, mod_path, MODULE_PATH_LEN) == 0) {
+			if (entry)
+				*entry = elem;
+			return 1;
+		}
+	} while ((elem = g_slist_next(elem)));
+
+	return 0;
+}
diff --git a/libfprint/module.h b/libfprint/module.h
new file mode 100644
index 0000000..f9cd74e
--- /dev/null
+++ b/libfprint/module.h
@@ -0,0 +1,57 @@
+/*
+ * Support for dynamically loading drivers
+ * Copyright (C) 2012 Kunal Gangakhedkar <kunal.gangakhedkar at gmail.com>
+ *
+ * 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 library 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 __FPRINT_MODULE_H__
+#define __FPRINT_MODULE_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <sys/param.h>
+#include <config.h>
+
+#define MODULE_PATH_LEN		MAXPATHLEN
+#define MODULE_NAME_LEN		MODULE_PATH_LEN
+
+typedef int (*initcall_t)(void);
+typedef void (*exitcall_t)(void);
+
+struct fp_mod {
+	char name[MODULE_NAME_LEN];
+	char path[MODULE_PATH_LEN];
+	initcall_t init;
+	exitcall_t exit;
+	void *handle;
+};
+
+#define module_init(initfn)			\
+	API_EXPORTED int init_mod(void) __attribute__((alias(#initfn)));
+
+#define module_exit(exitfn)			\
+	API_EXPORTED int cleanup_mod(void) __attribute__((alias(#exitfn)));
+
+int load_module(const char *modpath);
+int unload_module(const char *modpath);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* __FPRINT_MODULE_H__ */
-- 
1.7.9.5