subsys/tracing/tracing_backend_posix: Set file to be closed on exec

If the process does an exec() (or fork, or..) all descriptors are kept
open by default, unless O_CLOEXEC is set when opening them.
This is usefull for stdin/out/err so that new process is connected to
them, but it is very rare for it to be usefull for any other descriptor.

In general this leads to descriptors being kept open unnecessarily,
which either will block other process from getting them (for example
if the child survives the parent but it does something else).
Or for a "leak" which unnecessarily uses descriptors and memory in the
child process.

Let's ensure we do not leak it for this component as we do not need it.

Note glibc fopen supports the "e" modifier as an extension to pass
O_CLOEXEC to the open syscall.

Signed-off-by: Alberto Escolar Piedras <[email protected]>

Author: aescolar

subsys/tracing/tracing_backend_posix_bottom.c

@@ -12,7 +12,12 @@ void *tracing_backend_posix_init_bottom(const char *file_name)
 {
 	FILE *f;
 
+#if defined(__GLIBC_PREREQ) && __GLIBC_PREREQ(2, 7)
+	f = fopen(file_name, "wbe"); /* Set O_CLOEXEC flag which is supported in glibc >= 2.7 */
+#else
 	f = fopen(file_name, "wb");
+#endif
+
 	if (f == NULL) {
 		nsi_print_error_and_exit("%s: Could not open CTF backend file %s\n",
 					 __func__, file_name);