Remove unused relay daemon commands
[lttng-tools.git] / src / common / optional.h
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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 *
35 * LTTNG_OPTIONAL should be combined with the LTTNG_PACKED macro when
36 * used for IPC / network communication.
37 *
38 * Declaration example:
39 * struct my_struct {
40 * int a;
41 * LTTNG_OPTIONAL(int, b);
42 * };
43 *
44 * Usage example:
45 * struct my_struct foo = LTTNG_OPTIONAL_INIT;
46 *
47 * LTTNG_OPTIONAL_SET(&foo.b, 42);
48 * if (foo.b.is_set) {
49 * printf("%d", foo.b.value);
50 * }
51 *
52 * LTTNG_OPTIONAL_UNSET(&foo.b);
53 */
54#define LTTNG_OPTIONAL(type) \
55 struct { \
56 uint8_t is_set; \
57 type value; \
58 }
59
60/*
61 * This macro is available as a 'convenience' to allow sites that assume
62 * an optional value is set to assert() that it is set when accessing it.
63 *
64 * Since this returns the 'optional' by value, it is not suitable for all
65 * wrapped optional types. It is meant to be used with PODs.
66 */
67#define LTTNG_OPTIONAL_GET(optional) \
68 ({ \
69 assert(optional.is_set); \
70 optional.value; \
71 })
72
73/*
74 * Initialize an optional field.
75 *
76 * The wrapped field is set to the value it would gave if it had static storage
77 * duration.
78 */
79#define LTTNG_OPTIONAL_INIT { .is_set = 0 }
80
81/* Set the value of an optional field. */
82#define LTTNG_OPTIONAL_SET(field_ptr, val) \
83 (field_ptr)->value = val; \
84 (field_ptr)->is_set = 1;
85
86/* Put an optional field in the "unset" (NULL-ed) state. */
87#define LTTNG_OPTIONAL_UNSET(field_ptr) \
88 (field_ptr)->is_set = 0;
89
90#endif /* LTTNG_OPTIONAL_H */
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