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      1 /*
      2  * This file is part of ltrace.
      3  * Copyright (C) 2011,2012,2013 Petr Machata, Red Hat Inc.
      4  *
      5  * This program is free software; you can redistribute it and/or
      6  * modify it under the terms of the GNU General Public License as
      7  * published by the Free Software Foundation; either version 2 of the
      8  * License, or (at your option) any later version.
      9  *
     10  * This program is distributed in the hope that it will be useful, but
     11  * WITHOUT ANY WARRANTY; without even the implied warranty of
     12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     13  * General Public License for more details.
     14  *
     15  * You should have received a copy of the GNU General Public License
     16  * along with this program; if not, write to the Free Software
     17  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
     18  * 02110-1301 USA
     19  */
     20 
     21 #ifndef _CALLBACK_H_
     22 #define _CALLBACK_H_
     23 
     24 /* Notes on the iteration interface used across ltrace.  Typically the
     25  * iteration function looks something like this:
     26  *
     27  *   foo *each_foo(foo *start_after,
     28  *                 enum callback_status (*cb)(foo *f, void *data),
     29  *                 void *data);
     30  *
     31  * The iteration starts after the element designated by START_AFTER,
     32  * or at the first element if START_AFTER is NULL.  CB is then called
     33  * for each element of the collection.  DATA is passed verbatim to CB.
     34  * If CB returns CBS_STOP, the iteration stops and the current element
     35  * is returned.  That element can then be passed as START_AFTER to
     36  * restart the iteration.  NULL is returned when iteration ends.
     37  *
     38  * CBS_FAIL is not currently handled, and essentially means the same
     39  * thing as CBS_STOP.  There's no provision for returning error
     40  * states.  Errors need to be signaled to the caller via DATA,
     41  * together with any other data that the callback needs.
     42  *
     43  * A richer iteration interface looks like this:
     44  *
     45  *   struct each_foo_t {
     46  *	foo *restart;
     47  *	int status;
     48  *   } each_foo(foo *start_after,
     49  *		enum callback_status (*cb)(foo *f, void *data),
     50  *		void *data);
     51  *
     52  * These provide error handling.  The two-part structure encodes both
     53  * the restart cookie and status.  Status of 0 means success, negative
     54  * values signify failures.  Status of -1 is dedicated to failures in
     55  * user callback (such that the callback returns CBS_FAIL).  Other
     56  * negative values signal failures in the iteration mechanism itself.
     57  */
     58 enum callback_status {
     59 	CBS_STOP, /* The iteration should stop.  */
     60 	CBS_CONT, /* The iteration should continue.  */
     61 	CBS_FAIL, /* There was an error.  The iteration should stop
     62 		   * and return error.  */
     63 };
     64 
     65 #define CBS_STOP_IF(X) ((X) ? CBS_STOP : CBS_CONT)
     66 #define CBS_CONT_IF(X) ((X) ? CBS_CONT : CBS_STOP)
     67 
     68 #endif /* _CALLBACK_H_ */
     69