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 }