Introduce LTTNG_UST_MAP_POPULATE_POLICY environment variable

[lttng-ust.git] / src / common / populate.c

diff --git a/src/common/populate.c b/src/common/populate.c
new file mode 100644 (file)
index 0000000..b7f6bcc
--- /dev/null
+++ b/src/common/populate.c
@@ -0,0 +1,86 @@
+/*
+ * SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2024-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ */
+
+#define _LGPL_SOURCE
+#include "common/getenv.h"
+#include "common/logging.h"
+#include "common/populate.h"
+
+enum populate_policy {
+       POPULATE_UNSET,
+
+       POPULATE_NONE,
+       POPULATE_CPU_POSSIBLE,
+
+       POPULATE_UNKNOWN,
+};
+
+static enum populate_policy map_populate_policy = POPULATE_UNSET;
+
+static void init_map_populate_policy(void)
+{
+       const char *populate_env_str;
+
+       if (map_populate_policy != POPULATE_UNSET)
+               return;
+
+       populate_env_str = lttng_ust_getenv("LTTNG_UST_MAP_POPULATE_POLICY");
+       if (!populate_env_str) {
+               map_populate_policy = POPULATE_NONE;
+               return;
+       }
+       if (!strcmp(populate_env_str, "none")) {
+               map_populate_policy = POPULATE_NONE;
+       } else if (!strcmp(populate_env_str, "cpu_possible")) {
+               map_populate_policy = POPULATE_CPU_POSSIBLE;
+       } else {
+               /*
+                * populate_env_str is an untrusted environment variable
+                * input (can be provided to setuid/setgid binaries), so
+                * don't even try to print it.
+                */
+               WARN("Unknown policy for LTTNG_UST_MAP_POPULATE_POLICY environment variable.");
+               map_populate_policy = POPULATE_UNKNOWN;
+       }
+}
+
+/*
+ * Return the shared page populate policy for global pages. Returns true
+ * if shared memory pages should be pre-populated, false otherwise.
+ */
+bool lttng_ust_map_populate_is_enabled(void)
+{
+       init_map_populate_policy();
+
+       switch (map_populate_policy) {
+       case POPULATE_UNKNOWN:  /* Fall-through */
+       case POPULATE_NONE:
+               return false;
+       case POPULATE_CPU_POSSIBLE:
+               return true;
+       default:
+               abort();
+       }
+       return false;
+}
+
+/*
+ * Return the shared page populate policy based on the @cpu number
+ * provided as input. Returns true if shared memory pages should be
+ * pre-populated, false otherwise.
+ *
+ * The @cpu argument is currently unused except for negative value
+ * validation. It is present to eventually match cpu affinity or cpu
+ * online masks if those features are added in the future.
+ */
+bool lttng_ust_map_populate_cpu_is_enabled(int cpu)
+{
+       /* Reject invalid cpu number. */
+       if (cpu < 0)
+               return false;
+
+       return lttng_ust_map_populate_is_enabled();
+}