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