Add the trace chunk and trace chunk registry interfaces

[lttng-tools.git] / src / common / optional.h

diff --git a/src/common/optional.h b/src/common/optional.h
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+++ b/src/common/optional.h
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+/*
+ * Copyright (C) 2019 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2 only,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef LTTNG_OPTIONAL_H
+#define LTTNG_OPTIONAL_H
+
+#include <stdint.h>
+#include <assert.h>
+
+/*
+ * Define wrapper structure representing an optional value.
+ *
+ * This macro defines an "is_set" boolean field that must be checked
+ * when accessing the optional field. This "is_set" field provides
+ * the semantics that would be expected of a typical "raw pointer" field
+ * which would be checked for NULL.
+ *
+ * Prefer using this macro where "special" values would be used, e.g.
+ * -1ULL for uint64_t types.
+ *
+ * LTTNG_OPTIONAL should be combined with the LTTNG_PACKED macro when
+ * used for IPC / network communication.
+ *
+ * Declaration example:
+ * struct my_struct {
+ *     int a;
+ *     LTTNG_OPTIONAL(int, b);
+ * };
+ *
+ * Usage example:
+ * struct my_struct foo = LTTNG_OPTIONAL_INIT;
+ *
+ * LTTNG_OPTIONAL_SET(&foo.b, 42);
+ * if (foo.b.is_set) {
+ *     printf("%d", foo.b.value);
+ * }
+ *
+ * LTTNG_OPTIONAL_UNSET(&foo.b);
+ */
+#define LTTNG_OPTIONAL(type) \
+       struct {             \
+               uint8_t is_set; \
+               type value;  \
+       }
+
+/*
+ * This macro is available as a 'convenience' to allow sites that assume
+ * an optional value is set to assert() that it is set when accessing it.
+ *
+ * Since this returns the 'optional' by value, it is not suitable for all
+ * wrapped optional types. It is meant to be used with PODs.
+ */
+#define LTTNG_OPTIONAL_GET(optional)                   \
+        ({                                             \
+               assert(optional.is_set);                \
+               optional.value;                         \
+       })
+
+/*
+ * Initialize an optional field.
+ *
+ * The wrapped field is set to the value it would gave if it had static storage
+ * duration.
+ */
+#define LTTNG_OPTIONAL_INIT { .is_set = 0 }
+
+/* Set the value of an optional field. */
+#define LTTNG_OPTIONAL_SET(field_ptr, val) \
+       (field_ptr)->value = val;          \
+       (field_ptr)->is_set = 1;
+
+/* Put an optional field in the "unset" (NULL-ed) state. */
+#define LTTNG_OPTIONAL_UNSET(field_ptr)    \
+       (field_ptr)->is_set = 0;
+
+#endif /* LTTNG_OPTIONAL_H */