time: Add timens_offsets to be used for tasks in time namespace

Introduce offsets for time namespace. They will contain an adjustment
needed to convert clocks to/from host's.

A new namespace is created with the same offsets as the time namespace
of the current process.

Co-developed-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrei Vagin <avagin@openvz.org>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20191112012724.250792-5-dima@arista.com


diff --git a/kernel/time/namespace.c b/kernel/time/namespace.c
index 2662a69e..c2a58e4 100644
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -14,6 +14,7 @@
 #include <linux/slab.h>
 #include <linux/cred.h>
 #include <linux/err.h>
+#include <linux/mm.h>
 
 static struct ucounts *inc_time_namespaces(struct user_namespace *ns)
 {
@@ -60,6 +61,7 @@ static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
 	ns->ucounts = ucounts;
 	ns->ns.ops = &timens_operations;
 	ns->user_ns = get_user_ns(user_ns);
+	ns->offsets = old_ns->offsets;
 	return ns;
 
 fail_free: