3fe86405c112307a47e6c1abe0a9c62fe8b2175b
[lttng-ust.git] / liblttng-ust / lttng-context-vtid.c
1 /*
2 * (C) Copyright 2009-2011 -
3 * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
4 *
5 * LTTng UST vtid context.
6 *
7 * Dual LGPL v2.1/GPL v2 license.
8 */
9
10 #include <sys/types.h>
11 #include <unistd.h>
12 #include <lttng/ust-events.h>
13 #include <lttng/ust-tracer.h>
14 #include <lttng/ringbuffer-config.h>
15 #include <lttng/ust-tid.h>
16
17 /*
18 * We cache the result to ensure we don't trigger a system call for
19 * each event.
20 */
21 static __thread pid_t cached_vtid;
22
23 /*
24 * Upon fork or clone, the TID assigned to our thread is not the same as
25 * we kept in cache. Luckily, we are the only thread surviving in the
26 * child process, so we can simply clear our cached version.
27 */
28 void lttng_context_vtid_reset(void)
29 {
30 cached_vtid = 0;
31 }
32
33 static
34 size_t vtid_get_size(size_t offset)
35 {
36 size_t size = 0;
37
38 size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
39 size += sizeof(pid_t);
40 return size;
41 }
42
43 static
44 void vtid_record(struct lttng_ctx_field *field,
45 struct lttng_ust_lib_ring_buffer_ctx *ctx,
46 struct ltt_channel *chan)
47 {
48 if (caa_unlikely(!cached_vtid))
49 cached_vtid = gettid();
50 lib_ring_buffer_align_ctx(ctx, lttng_alignof(cached_vtid));
51 chan->ops->event_write(ctx, &cached_vtid, sizeof(cached_vtid));
52 }
53
54 int lttng_add_vtid_to_ctx(struct lttng_ctx **ctx)
55 {
56 struct lttng_ctx_field *field;
57
58 field = lttng_append_context(ctx);
59 if (!field)
60 return -ENOMEM;
61 if (lttng_find_context(*ctx, "vtid")) {
62 lttng_remove_context_field(ctx, field);
63 return -EEXIST;
64 }
65 field->event_field.name = "vtid";
66 field->event_field.type.atype = atype_integer;
67 field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
68 field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
69 field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_t);
70 field->event_field.type.u.basic.integer.reverse_byte_order = 0;
71 field->event_field.type.u.basic.integer.base = 10;
72 field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
73 field->get_size = vtid_get_size;
74 field->record = vtid_record;
75 return 0;
76 }
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