automatically update the database with Linux inotify

This patch implements a light-weight inotify library, and watches all
directories below the music directory.  It updates all directories
where files changed after a delay of 5 seconds.

src/inotify_queue.c

@@ -0,0 +1,134 @@
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "inotify_queue.h"
+#include "update.h"
+
+#include <glib.h>
+
+#include <string.h>
+
+#undef G_LOG_DOMAIN
+#define G_LOG_DOMAIN "inotify"
+
+enum {
+	/**
+	 * Wait this long after the last change before calling
+	 * update_enqueue().  This increases the probability that
+	 * updates can be bundled.
+	 */
+	INOTIFY_UPDATE_DELAY_MS = 5000,
+};
+
+static GSList *inotify_queue;
+static guint queue_source_id;
+
+void
+mpd_inotify_queue_init(void)
+{
+}
+
+static void
+free_callback(gpointer data, G_GNUC_UNUSED gpointer user_data)
+{
+	g_free(data);
+}
+
+void
+mpd_inotify_queue_finish(void)
+{
+	if (queue_source_id != 0)
+		g_source_remove(queue_source_id);
+
+	g_slist_foreach(inotify_queue, free_callback, NULL);
+	g_slist_free(inotify_queue);
+}
+
+static gboolean
+mpd_inotify_run_update(G_GNUC_UNUSED gpointer data)
+{
+	unsigned id;
+
+	while (inotify_queue != NULL) {
+		char *uri_utf8 = inotify_queue->data;
+
+		id = update_enqueue(uri_utf8, false);
+		if (id == 0)
+			/* retry later */
+			return true;
+
+		g_debug("updating '%s' job=%u", uri_utf8, id);
+
+		g_free(uri_utf8);
+		inotify_queue = g_slist_delete_link(inotify_queue,
+						    inotify_queue);
+	}
+
+	/* done, remove the timer event by returning false */
+	queue_source_id = 0;
+	return false;
+}
+
+static bool
+path_in(const char *path, const char *possible_parent)
+{
+	size_t length = strlen(possible_parent);
+
+	return path[0] == 0 ||
+		(memcmp(possible_parent, path, length) == 0 &&
+		 (path[length] == 0 || path[length] == '/'));
+}
+
+void
+mpd_inotify_enqueue(char *uri_utf8)
+{
+	GSList *old_queue = inotify_queue;
+
+	if (queue_source_id != 0)
+		g_source_remove(queue_source_id);
+	queue_source_id = g_timeout_add(INOTIFY_UPDATE_DELAY_MS,
+					mpd_inotify_run_update, NULL);
+
+	inotify_queue = NULL;
+	while (old_queue != NULL) {
+		char *current_uri = old_queue->data;
+
+		if (path_in(uri_utf8, current_uri)) {
+			/* already enqueued */
+			g_free(uri_utf8);
+			inotify_queue = g_slist_concat(inotify_queue,
+						       old_queue);
+			return;
+		}
+
+		old_queue = g_slist_delete_link(old_queue, old_queue);
+
+		if (path_in(current_uri, uri_utf8))
+			/* existing path is a sub-path of the new
+			   path; we can dequeue the existing path and
+			   update the new path instead */
+			g_free(current_uri);
+		else
+			/* move the existing path to the new queue */
+			inotify_queue = g_slist_prepend(inotify_queue,
+							current_uri);
+	}
+
+	inotify_queue = g_slist_prepend(inotify_queue, uri_utf8);
+}