Commit | Line | Data |
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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> | |
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 | * | |
2c5ff4e4 JG |
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 | ||
0a30bf9b JG |
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 | ||
2c5ff4e4 JG |
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) \ | |
a321667a | 65 | ({ \ |
bc2dc8d4 MD |
66 | assert((optional).is_set); \ |
67 | (optional).value; \ | |
2c5ff4e4 JG |
68 | }) |
69 | ||
3da864a9 JR |
70 | /* |
71 | * This macro is available as a 'convenience' to allow sites that assume | |
72 | * an optional value is set to assert() that it is set when fecthing the | |
73 | * underlying value's address. | |
74 | */ | |
75 | #define LTTNG_OPTIONAL_GET_PTR(optional) \ | |
76 | ({ \ | |
77 | assert((optional).is_set); \ | |
78 | &(optional).value; \ | |
79 | }) | |
80 | ||
2c5ff4e4 JG |
81 | /* |
82 | * Initialize an optional field. | |
83 | * | |
84 | * The wrapped field is set to the value it would gave if it had static storage | |
85 | * duration. | |
86 | */ | |
87 | #define LTTNG_OPTIONAL_INIT { .is_set = 0 } | |
88 | ||
89 | /* Set the value of an optional field. */ | |
bc2dc8d4 MD |
90 | #define LTTNG_OPTIONAL_SET(field_ptr, val) \ |
91 | do { \ | |
92 | (field_ptr)->value = (val); \ | |
93 | (field_ptr)->is_set = 1; \ | |
94 | } while (0) | |
2c5ff4e4 JG |
95 | |
96 | /* Put an optional field in the "unset" (NULL-ed) state. */ | |
bc2dc8d4 MD |
97 | #define LTTNG_OPTIONAL_UNSET(field_ptr) \ |
98 | do { \ | |
99 | (field_ptr)->is_set = 0; \ | |
100 | } while (0) | |
2c5ff4e4 JG |
101 | |
102 | #endif /* LTTNG_OPTIONAL_H */ |