[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>

/*
 * 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
2c5ff4e4	1	/*
ab5be9fa	2	* Copyright (C) 2019 Jérémie Galarneau <jeremie.galarneau@efficios.com>
2c5ff4e4	3	*
ab5be9fa	4	* SPDX-License-Identifier: GPL-2.0-only
2c5ff4e4	5	*
2c5ff4e4 JG	6	*/
	7
	8	#ifndef LTTNG_OPTIONAL_H
	9	#define LTTNG_OPTIONAL_H
	10
	11	#include <stdint.h>
2c5ff4e4 JG	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	*
2c5ff4e4 JG	24	* Declaration example:
	25	* struct my_struct {
	26	* int a;
8250d597	27	* LTTNG_OPTIONAL(int) b;
2c5ff4e4 JG	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
0a30bf9b JG	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
2c5ff4e4 JG	56	/*
2c5ff4e4 JG	57	* This macro is available as a 'convenience' to allow sites that assume
a0377dfe	58	* an optional value is set to LTTNG_ASSERT() that it is set when accessing it.
2c5ff4e4 JG	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) \
a321667a	64	({ \
a0377dfe	65	LTTNG_ASSERT((optional).is_set); \
bc2dc8d4	66	(optional).value; \
2c5ff4e4 JG	67	})
2c5ff4e4 JG	68
3da864a9 JR	69	/*
3da864a9 JR	70	* This macro is available as a 'convenience' to allow sites that assume
a0377dfe	71	* an optional value is set to LTTNG_ASSERT() that it is set when fecthing the
3da864a9 JR	72	* underlying value's address.
	73	*/
	74	#define LTTNG_OPTIONAL_GET_PTR(optional) \
	75	({ \
a0377dfe	76	LTTNG_ASSERT((optional).is_set); \
3da864a9 JR	77	&(optional).value; \
	78	})
	79
2c5ff4e4	80	/*
5747e45a	81	* Initialize an optional field as unset.
2c5ff4e4 JG	82	*
	83	* The wrapped field is set to the value it would gave if it had static storage
	84	* duration.
	85	*/
1c9a0b0e	86	#define LTTNG_OPTIONAL_INIT_UNSET {}
5747e45a JG	87
	88	/*
	89	* Initialize an optional field as 'set' with a given value.
	90	*/
7966af57	91	#define LTTNG_OPTIONAL_INIT_VALUE(val) { .is_set = 1, .value = val }
2c5ff4e4 JG	92
2c5ff4e4 JG	93	/* Set the value of an optional field. */
bc2dc8d4 MD	94	#define LTTNG_OPTIONAL_SET(field_ptr, val) \
bc2dc8d4 MD	95	do { \
bc2dc8d4	96	(field_ptr)->is_set = 1; \
7966af57	97	(field_ptr)->value = (val); \
bc2dc8d4	98	} while (0)
2c5ff4e4 JG	99
2c5ff4e4 JG	100	/* Put an optional field in the "unset" (NULL-ed) state. */
bc2dc8d4 MD	101	#define LTTNG_OPTIONAL_UNSET(field_ptr) \
	102	do { \
	103	(field_ptr)->is_set = 0; \
	104	} while (0)
2c5ff4e4 JG	105
2c5ff4e4 JG	106	#endif /* LTTNG_OPTIONAL_H */