lib/nfs/Base: kludge to reduce number of NFS mounts

Creating a NfsStorage sets its own export_name as the "base".  Now
NfsFileReader can use this information to derive the export_name to be
mounted, instead of guessing.  This solves the "too many connection"
problem on the NFS server while updating the database.

src/lib/nfs/Base.cxx

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2003-2014 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 "Base.hxx"
+
+#include <assert.h>
+#include <string.h>
+
+static char nfs_base_server[64];
+static char nfs_base_export_name[256];
+static size_t nfs_base_export_name_length;
+
+void
+nfs_set_base(const char *server, const char *export_name)
+{
+	assert(server != nullptr);
+	assert(export_name != nullptr);
+
+	const size_t server_length = strlen(server);
+	const size_t export_name_length = strlen(export_name);
+
+	if (server_length >= sizeof(nfs_base_server) ||
+	    export_name_length > sizeof(nfs_base_export_name))
+		return;
+
+	memcpy(nfs_base_server, server, server_length + 1);
+	memcpy(nfs_base_export_name, export_name, export_name_length);
+	nfs_base_export_name_length = export_name_length;
+}
+
+const char *
+nfs_check_base(const char *server, const char *path)
+{
+	assert(server != nullptr);
+	assert(path != nullptr);
+
+	return strcmp(nfs_base_server, server) == 0 &&
+	    memcmp(nfs_base_export_name, path,
+		   nfs_base_export_name_length) == 0 &&
+		(path[nfs_base_export_name_length] == 0 ||
+		 path[nfs_base_export_name_length] == '/')
+		? path + nfs_base_export_name_length
+		: nullptr;
+}