+/*
+ * (C) Copyright 2009-2011 -
+ * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * LTTng UST vtid context.
+ *
+ * Dual LGPL v2.1/GPL v2 license.
+ */
+
+#include <sys/types.h>
+#include <unistd.h>
+#include <ust/lttng-events.h>
+#include <ust/lttng-tracer.h>
+#include <ust/ringbuffer-config.h>
+
+#ifdef __linux__
+#include <syscall.h>
+#endif
+
+#if defined(_syscall0)
+_syscall0(pid_t, gettid)
+#elif defined(__NR_gettid)
+static inline pid_t gettid(void)
+{
+ return syscall(__NR_gettid);
+}
+#else
+#warning "use pid as tid"
+static inline pid_t gettid(void)
+{
+ return getpid();
+}
+#endif
+
+/*
+ * We cache the result to ensure we don't trigger a system call for
+ * each event.
+ */
+static __thread pid_t cached_vtid;
+
+static
+size_t vtid_get_size(size_t offset)
+{
+ size_t size = 0;
+
+ size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
+ size += sizeof(pid_t);
+ return size;
+}
+
+static
+void vtid_record(struct lttng_ctx_field *field,
+ struct lib_ring_buffer_ctx *ctx,
+ struct ltt_channel *chan)
+{
+ if (unlikely(!cached_vtid))
+ cached_vtid = gettid();
+ lib_ring_buffer_align_ctx(ctx, lttng_alignof(cached_vtid));
+ chan->ops->event_write(ctx, &cached_vtid, sizeof(cached_vtid));
+}
+
+int lttng_add_vtid_to_ctx(struct lttng_ctx **ctx)
+{
+ struct lttng_ctx_field *field;
+
+ field = lttng_append_context(ctx);
+ if (!field)
+ return -ENOMEM;
+ if (lttng_find_context(*ctx, "vtid")) {
+ lttng_remove_context_field(ctx, field);
+ return -EEXIST;
+ }
+ field->event_field.name = "vtid";
+ field->event_field.type.atype = atype_integer;
+ field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
+ field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
+ field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_t);
+ field->event_field.type.u.basic.integer.reverse_byte_order = 0;
+ field->event_field.type.u.basic.integer.base = 10;
+ field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
+ field->get_size = vtid_get_size;
+ field->record = vtid_record;
+ return 0;
+}