projects / lttng-tools.git / blame
| Commit | Line | Data |
|---|---|---|
| 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 */ |