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
  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 /*
  42  * Upon fork or clone, the TID assigned to our thread is not the same as
  43  * we kept in cache. Luckily, we are the only thread surviving in the
  44  * child process, so we can simply clear our cached version.
  45  */
  46 void lttng_context_vtid_reset(void)
  47 {
  48         cached_vtid = 0;
  49 }
  50
  51 static
  52 size_t vtid_get_size(size_t offset)
  53 {
  54         size_t size = 0;
  55
  56         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  57         size += sizeof(pid_t);
  58         return size;
  59 }
  60
  61 static
  62 void vtid_record(struct lttng_ctx_field *field,
  63                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  64                  struct ltt_channel *chan)
  65 {
  66         if (caa_unlikely(!cached_vtid))
  67                 cached_vtid = gettid();
  68         lib_ring_buffer_align_ctx(ctx, lttng_alignof(cached_vtid));
  69         chan->ops->event_write(ctx, &cached_vtid, sizeof(cached_vtid));
  70 }
  71
  72 int lttng_add_vtid_to_ctx(struct lttng_ctx **ctx)
  73 {
  74         struct lttng_ctx_field *field;
  75
  76         field = lttng_append_context(ctx);
  77         if (!field)
  78                 return -ENOMEM;
  79         if (lttng_find_context(*ctx, "vtid")) {
  80                 lttng_remove_context_field(ctx, field);
  81                 return -EEXIST;
  82         }
  83         field->event_field.name = "vtid";
  84         field->event_field.type.atype = atype_integer;
  85         field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
  86         field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
  87         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_t);
  88         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
  89         field->event_field.type.u.basic.integer.base = 10;
  90         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
  91         field->get_size = vtid_get_size;
  92         field->record = vtid_record;
  93         return 0;
  94 }