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