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 "ltt-tracer-core.h"
  16
  17 #ifdef __linux__
  18 #include <syscall.h>
  19 #endif
  20
  21 #if defined(_syscall0)
  22 _syscall0(pid_t, gettid)
  23 #elif defined(__NR_gettid)
  24 static inline pid_t gettid(void)
  25 {
  26         return syscall(__NR_gettid);
  27 }
  28 #else
  29 #warning "use pid as tid"
  30 static inline pid_t gettid(void)
  31 {
  32         return getpid();
  33 }
  34 #endif
  35
  36 /*
  37  * We cache the result to ensure we don't trigger a system call for
  38  * each event.
  39  */
  40 static __thread pid_t cached_vtid;
  41
  42 /*
  43  * Upon fork or clone, the TID assigned to our thread is not the same as
  44  * we kept in cache. Luckily, we are the only thread surviving in the
  45  * child process, so we can simply clear our cached version.
  46  */
  47 void lttng_context_vtid_reset(void)
  48 {
  49         cached_vtid = 0;
  50 }
  51
  52 static
  53 size_t vtid_get_size(size_t offset)
  54 {
  55         size_t size = 0;
  56
  57         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  58         size += sizeof(pid_t);
  59         return size;
  60 }
  61
  62 static
  63 void vtid_record(struct lttng_ctx_field *field,
  64                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  65                  struct ltt_channel *chan)
  66 {
  67         if (caa_unlikely(!cached_vtid))
  68                 cached_vtid = gettid();
  69         lib_ring_buffer_align_ctx(ctx, lttng_alignof(cached_vtid));
  70         chan->ops->event_write(ctx, &cached_vtid, sizeof(cached_vtid));
  71 }
  72
  73 int lttng_add_vtid_to_ctx(struct lttng_ctx **ctx)
  74 {
  75         struct lttng_ctx_field *field;
  76
  77         field = lttng_append_context(ctx);
  78         if (!field)
  79                 return -ENOMEM;
  80         if (lttng_find_context(*ctx, "vtid")) {
  81                 lttng_remove_context_field(ctx, field);
  82                 return -EEXIST;
  83         }
  84         field->event_field.name = "vtid";
  85         field->event_field.type.atype = atype_integer;
  86         field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
  87         field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
  88         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_t);
  89         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
  90         field->event_field.type.u.basic.integer.base = 10;
  91         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
  92         field->get_size = vtid_get_size;
  93         field->record = vtid_record;
  94         return 0;
  95 }
  96
  97 /*
  98  * Force a read (imply TLS fixup for dlopen) of TLS variables.
  99  */
 100 void lttng_fixup_vtid_tls(void)
 101 {
 102         asm volatile ("" : : "m" (cached_vtid));
 103 }