namespace: add lxc_raw_getpid()

src/lxc/namespace.h

@@ -23,8 +23,9 @@
 #ifndef __LXC_NAMESPACE_H
 #define __LXC_NAMESPACE_H
 
-#include <sys/syscall.h>
 #include <sched.h>
+#include <unistd.h>
+#include <sys/syscall.h>
 
 #include "config.h"
 
@@ -119,4 +120,13 @@ extern int lxc_namespace_2_cloneflag(const char *namespace);
 extern int lxc_namespace_2_ns_idx(const char *namespace);
 extern int lxc_fill_namespace_flags(char *flaglist, int *flags);
 
+/**
+ * Because of older glibc's pid cache (up to 2.25) whenever clone() is called
+ * the child must must retrieve it's own pid via lxc_raw_getpid().
+ */
+static inline pid_t lxc_raw_getpid(void)
+{
+	return (pid_t) syscall(SYS_getpid);
+}
+
 #endif