src/lib/lttng-ust-common/getcpu.c

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  */
   6
   7 #define _LGPL_SOURCE
   8 #include <dlfcn.h>
   9 #include <stdlib.h>
  10 #include <urcu/system.h>
  11 #include <urcu/arch.h>
  12
  13 #include "common/getcpu.h"
  14 #include "common/getenv.h"
  15 #include "common/logging.h"
  16
  17 #include "lib/lttng-ust-common/getcpu.h"
  18
  19 /* Function pointer to the current getcpu callback. */
  20 int (*lttng_ust_get_cpu_sym)(void);
  21
  22 static
  23 void *getcpu_plugin_handle;
  24
  25 /*
  26  * Override the user provided getcpu implementation.
  27  */
  28 int lttng_ust_getcpu_override(int (*getcpu)(void))
  29 {
  30         CMM_STORE_SHARED(lttng_ust_get_cpu_sym, getcpu);
  31         return 0;
  32 }
  33
  34 /*
  35  * Initialize the getcpu plugin if it's present.
  36  */
  37 void lttng_ust_getcpu_plugin_init(void)
  38 {
  39         const char *libname;
  40         void (*getcpu_plugin_init)(void);
  41
  42         /* If a plugin is already loaded, do nothing. */
  43         if (getcpu_plugin_handle)
  44                 return;
  45
  46         /*
  47          * If the LTTNG_UST_GETCPU_PLUGIN environment variable is undefined, do
  48          * nothing.
  49          */
  50         libname = lttng_ust_getenv("LTTNG_UST_GETCPU_PLUGIN");
  51         if (!libname)
  52                 return;
  53
  54         /*
  55          * Thy to dlopen the getcpu plugin shared object specified in
  56          * LTTNG_UST_GETCPU_PLUGIN.
  57          */
  58         getcpu_plugin_handle = dlopen(libname, RTLD_NOW);
  59         if (!getcpu_plugin_handle) {
  60                 PERROR("Cannot load LTTng UST getcpu override library %s",
  61                         libname);
  62                 return;
  63         }
  64         dlerror();
  65
  66         /* Locate the getcpu plugin init function in the shared object. */
  67         getcpu_plugin_init = (void (*)(void)) dlsym(getcpu_plugin_handle,
  68                 "lttng_ust_getcpu_plugin_init");
  69         if (!getcpu_plugin_init) {
  70                 PERROR("Cannot find LTTng UST getcpu override library %s initialization function lttng_ust_getcpu_plugin_init()",
  71                         libname);
  72                 return;
  73         }
  74
  75         /* Run the user provided getcpu plugin init function. */
  76         getcpu_plugin_init();
  77 }