libust/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 <ust/lttng-events.h>
  13 #include <ust/lttng-tracer.h>
  14 #include <ust/ringbuffer-config.h>
  15
  16 #ifdef __linux__
  17 #include <syscall.h>
  18 #endif
  19
  20 #if defined(_syscall0)
  21 _syscall0(pid_t, gettid)
  22 #elif defined(__NR_gettid)
  23 static inline pid_t gettid(void)
  24 {
  25         return syscall(__NR_gettid);
  26 }
  27 #else
  28 #warning "use pid as tid"
  29 static inline pid_t gettid(void)
  30 {
  31         return getpid();
  32 }
  33 #endif
  34
  35 /*
  36  * We cache the result to ensure we don't trigger a system call for
  37  * each event.
  38  */
  39 static __thread pid_t cached_vtid;
  40
  41 static
  42 size_t vtid_get_size(size_t offset)
  43 {
  44         size_t size = 0;
  45
  46         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  47         size += sizeof(pid_t);
  48         return size;
  49 }
  50
  51 static
  52 void vtid_record(struct lttng_ctx_field *field,
  53                  struct lib_ring_buffer_ctx *ctx,
  54                  struct ltt_channel *chan)
  55 {
  56         if (unlikely(!cached_vtid))
  57                 cached_vtid = gettid();
  58         lib_ring_buffer_align_ctx(ctx, lttng_alignof(cached_vtid));
  59         chan->ops->event_write(ctx, &cached_vtid, sizeof(cached_vtid));
  60 }
  61
  62 int lttng_add_vtid_to_ctx(struct lttng_ctx **ctx)
  63 {
  64         struct lttng_ctx_field *field;
  65
  66         field = lttng_append_context(ctx);
  67         if (!field)
  68                 return -ENOMEM;
  69         if (lttng_find_context(*ctx, "vtid")) {
  70                 lttng_remove_context_field(ctx, field);
  71                 return -EEXIST;
  72         }
  73         field->event_field.name = "vtid";
  74         field->event_field.type.atype = atype_integer;
  75         field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
  76         field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
  77         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_t);
  78         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
  79         field->event_field.type.u.basic.integer.base = 10;
  80         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
  81         field->get_size = vtid_get_size;
  82         field->record = vtid_record;
  83         return 0;
  84 }