Add isc_os_umask() function to get current umask

As it's impossible to get the current umask without modifying it at the
same time, initialize the current umask at the program start and keep
the loaded value internally.  Add isc_os_umask() function to access the
starttime umask.

lib/isc/include/isc/os.h

@@ -14,6 +14,7 @@
 #pragma once
 
 /*! \file isc/os.h */
+#include <sys/stat.h>
 
 #include <isc/lang.h>
 #include <isc/types.h>
@@ -37,9 +38,15 @@ isc_os_ncpus(void);
 unsigned long
 isc_os_cacheline(void);
 /*%<
- * Return L1 caheline size of the CPU.
+ * Return L1 cacheline size of the CPU.
  * If L1 cache is greater than ISC_OS_CACHELINE_SIZE, ensure it is used
  * instead of constant. Is common on ppc64le architecture.
  */
 
+mode_t
+isc_os_umask(void);
+/*%<
+ * Return umask of the current process as initialized at the program start
+ */
+
 ISC_LANG_ENDDECLS

lib/isc/os.c

@@ -12,6 +12,7 @@
  */
 
 #include <inttypes.h>
+#include <sys/stat.h>
 
 #include <isc/os.h>
 #include <isc/types.h>
@@ -21,6 +22,7 @@
 
 static unsigned int isc__os_ncpus = 0;
 static unsigned long isc__os_cacheline = ISC_OS_CACHELINE_SIZE;
+static mode_t isc__os_umask = 0;
 
 #ifdef HAVE_SYSCONF
 
@@ -72,6 +74,12 @@ ncpus_initialize(void) {
 	}
 }
 
+static void
+umask_initialize(void) {
+	isc__os_umask = umask(0);
+	(void)umask(isc__os_umask);
+}
+
 unsigned int
 isc_os_ncpus(void) {
 	return (isc__os_ncpus);
@@ -82,8 +90,14 @@ isc_os_cacheline(void) {
 	return (isc__os_cacheline);
 }
 
+mode_t
+isc_os_umask(void) {
+	return (isc__os_umask);
+}
+
 void
 isc__os_initialize(void) {
+	umask_initialize();
 	ncpus_initialize();
 #if defined(HAVE_SYSCONF) && defined(_SC_LEVEL1_DCACHE_LINESIZE)
 	long s = sysconf(_SC_LEVEL1_DCACHE_LINESIZE);