[lttng-tools.git] / src / common / optional.h

/*
 * Copyright (C) 2019 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License, version 2 only,
 * as published by the Free Software Foundation.
 *
 * 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.
 */

#ifndef LTTNG_OPTIONAL_H
#define LTTNG_OPTIONAL_H

#include <stdint.h>
#include <assert.h>

/*
 * Define wrapper structure representing an optional value.
 *
 * This macro defines an "is_set" boolean field that must be checked
 * when accessing the optional field. This "is_set" field provides
 * the semantics that would be expected of a typical "raw pointer" field
 * which would be checked for NULL.
 *
 * Prefer using this macro where "special" values would be used, e.g.
 * -1ULL for uint64_t types.
 *
 * Declaration example:
 * struct my_struct {
 * 	int a;
 * 	LTTNG_OPTIONAL(int, b);
 * };
 *
 * Usage example:
 * struct my_struct foo = LTTNG_OPTIONAL_INIT;
 *
 * LTTNG_OPTIONAL_SET(&foo.b, 42);
 * if (foo.b.is_set) {
 * 	printf("%d", foo.b.value);
 * }
 *
 * LTTNG_OPTIONAL_UNSET(&foo.b);
 */
#define LTTNG_OPTIONAL(type) \
	struct {             \
		uint8_t is_set; \
		type value;  \
	}

/*
 * Alias used for communication structures. If the layout of an LTTNG_OPTIONAL
 * is changed, the original layout should still be used for communication
 * purposes.
 *
 * LTTNG_OPTIONAL_COMM should be combined with the LTTNG_PACKED macro when
 * used for IPC / network communication.
 */
#define LTTNG_OPTIONAL_COMM LTTNG_OPTIONAL

/*
 * This macro is available as a 'convenience' to allow sites that assume
 * an optional value is set to assert() that it is set when accessing it.
 *
 * Since this returns the 'optional' by value, it is not suitable for all
 * wrapped optional types. It is meant to be used with PODs.
 */
#define LTTNG_OPTIONAL_GET(optional)			\
        ({						\
		assert((optional).is_set);		\
		(optional).value;			\
	})

/*
 * Initialize an optional field.
 *
 * The wrapped field is set to the value it would gave if it had static storage
 * duration.
 */
#define LTTNG_OPTIONAL_INIT { .is_set = 0 }

/* Set the value of an optional field. */
#define LTTNG_OPTIONAL_SET(field_ptr, val)	\
	do {					\
		(field_ptr)->value = (val);	\
		(field_ptr)->is_set = 1;	\
	} while (0)

/* Put an optional field in the "unset" (NULL-ed) state. */
#define LTTNG_OPTIONAL_UNSET(field_ptr)		\
	do {					\
		(field_ptr)->is_set = 0;	\
	} while (0)

#endif /* LTTNG_OPTIONAL_H */
Commit	Line	Data
2c5ff4e4 JG	1	/*
	2	* Copyright (C) 2019 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
	3	*
	4	* This program is free software; you can redistribute it and/or modify
	5	* it under the terms of the GNU General Public License, version 2 only,
	6	* as published by the Free Software Foundation.
	7	*
	8	* This program is distributed in the hope that it will be useful, but WITHOUT
	9	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	10	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
	11	* more details.
	12	*
	13	* You should have received a copy of the GNU General Public License along
	14	* with this program; if not, write to the Free Software Foundation, Inc.,
	15	* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
	16	*/
	17
	18	#ifndef LTTNG_OPTIONAL_H
	19	#define LTTNG_OPTIONAL_H
	20
	21	#include <stdint.h>
	22	#include <assert.h>
	23
	24	/*
	25	* Define wrapper structure representing an optional value.
	26	*
	27	* This macro defines an "is_set" boolean field that must be checked
	28	* when accessing the optional field. This "is_set" field provides
	29	* the semantics that would be expected of a typical "raw pointer" field
	30	* which would be checked for NULL.
	31	*
	32	* Prefer using this macro where "special" values would be used, e.g.
	33	* -1ULL for uint64_t types.
	34	*
2c5ff4e4 JG	35	* Declaration example:
	36	* struct my_struct {
	37	* int a;
	38	* LTTNG_OPTIONAL(int, b);
	39	* };
	40	*
	41	* Usage example:
	42	* struct my_struct foo = LTTNG_OPTIONAL_INIT;
	43	*
	44	* LTTNG_OPTIONAL_SET(&foo.b, 42);
	45	* if (foo.b.is_set) {
	46	* printf("%d", foo.b.value);
	47	* }
	48	*
	49	* LTTNG_OPTIONAL_UNSET(&foo.b);
	50	*/
	51	#define LTTNG_OPTIONAL(type) \
	52	struct { \
	53	uint8_t is_set; \
	54	type value; \
	55	}
	56
0a30bf9b JG	57	/*
	58	* Alias used for communication structures. If the layout of an LTTNG_OPTIONAL
	59	* is changed, the original layout should still be used for communication
	60	* purposes.
	61	*
	62	* LTTNG_OPTIONAL_COMM should be combined with the LTTNG_PACKED macro when
	63	* used for IPC / network communication.
	64	*/
	65	#define LTTNG_OPTIONAL_COMM LTTNG_OPTIONAL
	66
2c5ff4e4 JG	67	/*
	68	* This macro is available as a 'convenience' to allow sites that assume
	69	* an optional value is set to assert() that it is set when accessing it.
	70	*
	71	* Since this returns the 'optional' by value, it is not suitable for all
	72	* wrapped optional types. It is meant to be used with PODs.
	73	*/
	74	#define LTTNG_OPTIONAL_GET(optional) \
	75	({ \
bc2dc8d4 MD	76	assert((optional).is_set); \
bc2dc8d4 MD	77	(optional).value; \
2c5ff4e4 JG	78	})
	79
	80	/*
	81	* Initialize an optional field.
	82	*
	83	* The wrapped field is set to the value it would gave if it had static storage
	84	* duration.
	85	*/
	86	#define LTTNG_OPTIONAL_INIT { .is_set = 0 }
	87
	88	/* Set the value of an optional field. */
bc2dc8d4 MD	89	#define LTTNG_OPTIONAL_SET(field_ptr, val) \
	90	do { \
	91	(field_ptr)->value = (val); \
	92	(field_ptr)->is_set = 1; \
	93	} while (0)
2c5ff4e4 JG	94
2c5ff4e4 JG	95	/* Put an optional field in the "unset" (NULL-ed) state. */
bc2dc8d4 MD	96	#define LTTNG_OPTIONAL_UNSET(field_ptr) \
	97	do { \
	98	(field_ptr)->is_set = 0; \
	99	} while (0)
2c5ff4e4 JG	100
2c5ff4e4 JG	101	#endif /* LTTNG_OPTIONAL_H */