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2c5ff4e4 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 */ |