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 #include "ltt-tracer-core.h"
  17
  18 /*
  19  * We cache the result to ensure we don't trigger a system call for
  20  * each event.
  21  */
  22 static __thread pid_t cached_vtid;
  23
  24 /*
  25  * Upon fork or clone, the TID assigned to our thread is not the same as
  26  * we kept in cache. Luckily, we are the only thread surviving in the
  27  * child process, so we can simply clear our cached version.
  28  */
  29 void lttng_context_vtid_reset(void)
  30 {
  31         cached_vtid = 0;
  32 }
  33
  34 static
  35 size_t vtid_get_size(size_t offset)
  36 {
  37         size_t size = 0;
  38
  39         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  40         size += sizeof(pid_t);
  41         return size;
  42 }
  43
  44 static
  45 void vtid_record(struct lttng_ctx_field *field,
  46                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  47                  struct ltt_channel *chan)
  48 {
  49         if (caa_unlikely(!cached_vtid))
  50                 cached_vtid = gettid();
  51         lib_ring_buffer_align_ctx(ctx, lttng_alignof(cached_vtid));
  52         chan->ops->event_write(ctx, &cached_vtid, sizeof(cached_vtid));
  53 }
  54
  55 int lttng_add_vtid_to_ctx(struct lttng_ctx **ctx)
  56 {
  57         struct lttng_ctx_field *field;
  58
  59         field = lttng_append_context(ctx);
  60         if (!field)
  61                 return -ENOMEM;
  62         if (lttng_find_context(*ctx, "vtid")) {
  63                 lttng_remove_context_field(ctx, field);
  64                 return -EEXIST;
  65         }
  66         field->event_field.name = "vtid";
  67         field->event_field.type.atype = atype_integer;
  68         field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
  69         field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
  70         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_t);
  71         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
  72         field->event_field.type.u.basic.integer.base = 10;
  73         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
  74         field->get_size = vtid_get_size;
  75         field->record = vtid_record;
  76         return 0;
  77 }
  78
  79 /*
  80  * Force a read (imply TLS fixup for dlopen) of TLS variables.
  81  */
  82 void lttng_fixup_vtid_tls(void)
  83 {
  84         asm volatile ("" : : "m" (cached_vtid));
  85 }