src/common/populate.c

   1 /*
   2  * SPDX-License-Identifier: MIT
   3  *
   4  * Copyright (C) 2024-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  */
   6
   7 #define _LGPL_SOURCE
   8 #include "common/getenv.h"
   9 #include "common/logging.h"
  10 #include "common/populate.h"
  11
  12 enum populate_policy {
  13         POPULATE_UNSET,
  14
  15         POPULATE_NONE,
  16         POPULATE_CPU_POSSIBLE,
  17
  18         POPULATE_UNKNOWN,
  19 };
  20
  21 static enum populate_policy map_populate_policy = POPULATE_UNSET;
  22
  23 static void init_map_populate_policy(void)
  24 {
  25         const char *populate_env_str;
  26
  27         if (map_populate_policy != POPULATE_UNSET)
  28                 return;
  29
  30         populate_env_str = lttng_ust_getenv("LTTNG_UST_MAP_POPULATE_POLICY");
  31         if (!populate_env_str) {
  32                 map_populate_policy = POPULATE_NONE;
  33                 return;
  34         }
  35         if (!strcmp(populate_env_str, "none")) {
  36                 map_populate_policy = POPULATE_NONE;
  37         } else if (!strcmp(populate_env_str, "cpu_possible")) {
  38                 map_populate_policy = POPULATE_CPU_POSSIBLE;
  39         } else {
  40                 /*
  41                  * populate_env_str is an untrusted environment variable
  42                  * input (can be provided to setuid/setgid binaries), so
  43                  * don't even try to print it.
  44                  */
  45                 WARN("Unknown policy for LTTNG_UST_MAP_POPULATE_POLICY environment variable.");
  46                 map_populate_policy = POPULATE_UNKNOWN;
  47         }
  48 }
  49
  50 /*
  51  * Return the shared page populate policy for global pages. Returns true
  52  * if shared memory pages should be pre-populated, false otherwise.
  53  */
  54 bool lttng_ust_map_populate_is_enabled(void)
  55 {
  56         init_map_populate_policy();
  57
  58         switch (map_populate_policy) {
  59         case POPULATE_UNKNOWN:  /* Fall-through */
  60         case POPULATE_NONE:
  61                 return false;
  62         case POPULATE_CPU_POSSIBLE:
  63                 return true;
  64         default:
  65                 abort();
  66         }
  67         return false;
  68 }
  69
  70 /*
  71  * Return the shared page populate policy based on the @cpu number
  72  * provided as input. Returns true if shared memory pages should be
  73  * pre-populated, false otherwise.
  74  *
  75  * The @cpu argument is currently unused except for negative value
  76  * validation. It is present to eventually match cpu affinity or cpu
  77  * online masks if those features are added in the future.
  78  */
  79 bool lttng_ust_map_populate_cpu_is_enabled(int cpu)
  80 {
  81         /* Reject invalid cpu number. */
  82         if (cpu < 0)
  83                 return false;
  84
  85         return lttng_ust_map_populate_is_enabled();
  86 }