2 * Copyright (C) 2019 Jérémie Galarneau <jeremie.galarneau@efficios.com>
4 * SPDX-License-Identifier: GPL-2.0-only
8 #ifndef LTTNG_OPTIONAL_H
9 #define LTTNG_OPTIONAL_H
15 * Define wrapper structure representing an optional value.
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.
22 * Prefer using this macro where "special" values would be used, e.g.
23 * -1ULL for uint64_t types.
25 * Declaration example:
28 * LTTNG_OPTIONAL(int, b);
32 * struct my_struct foo = LTTNG_OPTIONAL_INIT;
34 * LTTNG_OPTIONAL_SET(&foo.b, 42);
36 * printf("%d", foo.b.value);
39 * LTTNG_OPTIONAL_UNSET(&foo.b);
41 #define LTTNG_OPTIONAL(type) \
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
52 * LTTNG_OPTIONAL_COMM should be combined with the LTTNG_PACKED macro when
53 * used for IPC / network communication.
55 #define LTTNG_OPTIONAL_COMM LTTNG_OPTIONAL
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.
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.
64 #define LTTNG_OPTIONAL_GET(optional) \
66 assert((optional).is_set); \
71 * Initialize an optional field.
73 * The wrapped field is set to the value it would gave if it had static storage
76 #define LTTNG_OPTIONAL_INIT { .is_set = 0 }
78 /* Set the value of an optional field. */
79 #define LTTNG_OPTIONAL_SET(field_ptr, val) \
81 (field_ptr)->value = (val); \
82 (field_ptr)->is_set = 1; \
85 /* Put an optional field in the "unset" (NULL-ed) state. */
86 #define LTTNG_OPTIONAL_UNSET(field_ptr) \
88 (field_ptr)->is_set = 0; \
91 #endif /* LTTNG_OPTIONAL_H */
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