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

/*
 * 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>

/*
 * 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 LTTNG_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)			\
	({						\
		LTTNG_ASSERT((optional).is_set);		\
		(optional).value;			\
	})

/*
 * This macro is available as a 'convenience' to allow sites that assume
 * an optional value is set to LTTNG_ASSERT() that it is set when fecthing the
 * underlying value's address.
 */
#define LTTNG_OPTIONAL_GET_PTR(optional)			\
	({						\
		LTTNG_ASSERT((optional).is_set);		\
		&(optional).value;			\
	})

/*
 * Initialize an optional field as unset.
 *
 * The wrapped field is set to the value it would gave if it had static storage
 * duration.
 */
#define LTTNG_OPTIONAL_INIT_UNSET {}

/*
 * Initialize an optional field as 'set' with a given value.
 */
#define LTTNG_OPTIONAL_INIT_VALUE(val)      \
	{                                   \
		.is_set = 1, .value = (val) \
	}

/* Set the value of an optional field. */
#define LTTNG_OPTIONAL_SET(field_ptr, val)	\
	do {					\
		(field_ptr)->is_set = 1;	\
		(field_ptr)->value = (val);	\
	} 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
	13	/*
	14	* Define wrapper structure representing an optional value.
	15	*
	16	* This macro defines an "is_set" boolean field that must be checked
	17	* when accessing the optional field. This "is_set" field provides
	18	* the semantics that would be expected of a typical "raw pointer" field
	19	* which would be checked for NULL.
	20	*
	21	* Prefer using this macro where "special" values would be used, e.g.
	22	* -1ULL for uint64_t types.
	23	*
	24	* Declaration example:
	25	* struct my_struct {
	26	* int a;
	27	* LTTNG_OPTIONAL(int) b;
	28	* };
	29	*
	30	* Usage example:
	31	* struct my_struct foo = LTTNG_OPTIONAL_INIT;
	32	*
	33	* LTTNG_OPTIONAL_SET(&foo.b, 42);
	34	* if (foo.b.is_set) {
	35	* printf("%d", foo.b.value);
	36	* }
	37	*
	38	* LTTNG_OPTIONAL_UNSET(&foo.b);
	39	*/
	40	#define LTTNG_OPTIONAL(type) \
	41	struct { \
	42	uint8_t is_set; \
	43	type value; \
	44	}
	45
	46	/*
	47	* Alias used for communication structures. If the layout of an LTTNG_OPTIONAL
	48	* is changed, the original layout should still be used for communication
	49	* purposes.
	50	*
	51	* LTTNG_OPTIONAL_COMM should be combined with the LTTNG_PACKED macro when
	52	* used for IPC / network communication.
	53	*/
	54	#define LTTNG_OPTIONAL_COMM LTTNG_OPTIONAL
	55
	56	/*
	57	* This macro is available as a 'convenience' to allow sites that assume
	58	* an optional value is set to LTTNG_ASSERT() that it is set when accessing it.
	59	*
	60	* Since this returns the 'optional' by value, it is not suitable for all
	61	* wrapped optional types. It is meant to be used with PODs.
	62	*/
	63	#define LTTNG_OPTIONAL_GET(optional) \
	64	({ \
	65	LTTNG_ASSERT((optional).is_set); \
	66	(optional).value; \
	67	})
	68
	69	/*
	70	* This macro is available as a 'convenience' to allow sites that assume
	71	* an optional value is set to LTTNG_ASSERT() that it is set when fecthing the
	72	* underlying value's address.
	73	*/
	74	#define LTTNG_OPTIONAL_GET_PTR(optional) \
	75	({ \
	76	LTTNG_ASSERT((optional).is_set); \
	77	&(optional).value; \
	78	})
	79
	80	/*
	81	* Initialize an optional field as unset.
	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_UNSET {}
	87
	88	/*
	89	* Initialize an optional field as 'set' with a given value.
	90	*/
	91	#define LTTNG_OPTIONAL_INIT_VALUE(val) \
	92	{ \
	93	.is_set = 1, .value = (val) \
	94	}
	95
	96	/* Set the value of an optional field. */
	97	#define LTTNG_OPTIONAL_SET(field_ptr, val) \
	98	do { \
	99	(field_ptr)->is_set = 1; \
	100	(field_ptr)->value = (val); \
	101	} while (0)
	102
	103	/* Put an optional field in the "unset" (NULL-ed) state. */
	104	#define LTTNG_OPTIONAL_UNSET(field_ptr) \
	105	do { \
	106	(field_ptr)->is_set = 0; \
	107	} while (0)
	108
	109	#endif /* LTTNG_OPTIONAL_H */