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+/*
+ * This file is part of ltrace.
+ * Copyright (C) 2011,2012 Petr Machata, Red Hat Inc.
+ *
+ * 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 St, Fifth Floor, Boston, MA
+ * 02110-1301 USA
+ */
+
+#ifndef _CALLBACK_H_
+#define _CALLBACK_H_
+
+/* Notes on the iteration interface used across ltrace.  Typically the
+ * iteration function looks something like this:
+ *
+ *   foo *each_foo(foo *start_after,
+ *                 enum callback_status (*cb)(foo *f, void *data),
+ *                 void *data);
+ *
+ * The iteration starts after the element designated by START_AFTER,
+ * or at the first element if START_AFTER is NULL.  CB is then called
+ * for each element of the collection.  DATA is passed verbatim to CB.
+ * If CB returns CBS_STOP, the iteration stops and the current element
+ * is returned.  That element can then be passed as START_AFTER to
+ * restart the iteration.  NULL is returned when iteration ends.
+ *
+ * CBS_FAIL is not currently handled, and essentially means the same
+ * thing as CBS_STOP.  There's no provision for returning error
+ * states.  Errors need to be signaled to the caller via DATA,
+ * together with any other data that the callback needs.
+ */
+enum callback_status {
+	CBS_STOP, /* The iteration should stop.  */
+	CBS_CONT, /* The iteration should continue.  */
+	CBS_FAIL, /* There was an error.  The iteration should stop
+		   * and return error.  */
+};
+
+#endif /* _CALLBACK_H_ */