update: store playlist files in database

Don't open the music directory for each "lsinfo" call.  Get the list
of playlist files from the memory database.

src/playlist_database.c

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2003-2010 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 "config.h"
+#include "playlist_database.h"
+#include "playlist_vector.h"
+#include "text_file.h"
+
+#include <string.h>
+#include <stdlib.h>
+
+static GQuark
+playlist_database_quark(void)
+{
+	return g_quark_from_static_string("playlist_database");
+}
+
+void
+playlist_vector_save(FILE *fp, const struct playlist_vector *pv)
+{
+	for (const struct playlist_metadata *pm = pv->head;
+	     pm != NULL; pm = pm->next)
+		fprintf(fp, PLAYLIST_META_BEGIN "%s\n"
+			"mtime: %li\n"
+			"playlist_end\n",
+			pm->name, (long)pm->mtime);
+}
+
+bool
+playlist_metadata_load(FILE *fp, struct playlist_vector *pv, const char *name,
+		       GString *buffer, GError **error_r)
+{
+	struct playlist_metadata pm;
+	char *line, *colon;
+	const char *value;
+
+	while ((line = read_text_line(fp, buffer)) != NULL &&
+	       strcmp(line, "playlist_end") != 0) {
+		colon = strchr(line, ':');
+		if (colon == NULL || colon == line) {
+			g_set_error(error_r, playlist_database_quark(), 0,
+				    "unknown line in db: %s", line);
+			return false;
+		}
+
+		*colon++ = 0;
+		value = g_strchug(colon);
+
+		if (strcmp(line, "mtime") == 0)
+			pm.mtime = strtol(value, NULL, 10);
+		else {
+			g_set_error(error_r, playlist_database_quark(), 0,
+				    "unknown line in db: %s", line);
+			return false;
+		}
+	}
+
+	playlist_vector_update_or_add(pv, name, pm.mtime);
+	return true;
+}