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

/*
 * Copyright (C) 2019 Jérémie Galarneau <jeremie.galarneau@efficios.com>
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 */

#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
	1	/*
	2	* Copyright (C) 2019 Jérémie Galarneau <jeremie.galarneau@efficios.com>
	3	*
	4	* SPDX-License-Identifier: GPL-2.0-only
	5	*
	6	*/
	7
	8	#ifndef LTTNG_OPTIONAL_H
	9	#define LTTNG_OPTIONAL_H
	10
	11	#include <stdint.h>
	12	#include <assert.h>
	13
	14	/*
	15	* Define wrapper structure representing an optional value.
	16	*
	17	* This macro defines an "is_set" boolean field that must be checked
	18	* when accessing the optional field. This "is_set" field provides
	19	* the semantics that would be expected of a typical "raw pointer" field
	20	* which would be checked for NULL.
	21	*
	22	* Prefer using this macro where "special" values would be used, e.g.
	23	* -1ULL for uint64_t types.
	24	*
	25	* Declaration example:
	26	* struct my_struct {
	27	* int a;
	28	* LTTNG_OPTIONAL(int, b);
	29	* };
	30	*
	31	* Usage example:
	32	* struct my_struct foo = LTTNG_OPTIONAL_INIT;
	33	*
	34	* LTTNG_OPTIONAL_SET(&foo.b, 42);
	35	* if (foo.b.is_set) {
	36	* printf("%d", foo.b.value);
	37	* }
	38	*
	39	* LTTNG_OPTIONAL_UNSET(&foo.b);
	40	*/
	41	#define LTTNG_OPTIONAL(type) \
	42	struct { \
	43	uint8_t is_set; \
	44	type value; \
	45	}
	46
	47	/*
	48	* Alias used for communication structures. If the layout of an LTTNG_OPTIONAL
	49	* is changed, the original layout should still be used for communication
	50	* purposes.
	51	*
	52	* LTTNG_OPTIONAL_COMM should be combined with the LTTNG_PACKED macro when
	53	* used for IPC / network communication.
	54	*/
	55	#define LTTNG_OPTIONAL_COMM LTTNG_OPTIONAL
	56
	57	/*
	58	* This macro is available as a 'convenience' to allow sites that assume
	59	* an optional value is set to assert() that it is set when accessing it.
	60	*
	61	* Since this returns the 'optional' by value, it is not suitable for all
	62	* wrapped optional types. It is meant to be used with PODs.
	63	*/
	64	#define LTTNG_OPTIONAL_GET(optional) \
	65	({ \
	66	assert((optional).is_set); \
	67	(optional).value; \
	68	})
	69
	70	/*
	71	* Initialize an optional field.
	72	*
	73	* The wrapped field is set to the value it would gave if it had static storage
	74	* duration.
	75	*/
	76	#define LTTNG_OPTIONAL_INIT { .is_set = 0 }
	77
	78	/* Set the value of an optional field. */
	79	#define LTTNG_OPTIONAL_SET(field_ptr, val) \
	80	do { \
	81	(field_ptr)->value = (val); \
	82	(field_ptr)->is_set = 1; \
	83	} while (0)
	84
	85	/* Put an optional field in the "unset" (NULL-ed) state. */
	86	#define LTTNG_OPTIONAL_UNSET(field_ptr) \
	87	do { \
	88	(field_ptr)->is_set = 0; \
	89	} while (0)
	90
	91	#endif /* LTTNG_OPTIONAL_H */