rlimits: redo do_setrlimit to more generic do_prlimit

It now allows also reading of limits. I.e. all read and writes will
later use this function.

It takes two parameters, new and old limits which can be both NULL.
If new is non-NULL, the value in it is set to rlimits.
If old is non-NULL, current rlimits are stored there.
If both are non-NULL, old are stored prior to setting the new ones,
atomically.
(Similar to sigaction.)

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
diff --git a/include/linux/resource.h b/include/linux/resource.h
index 037aa7e..88d36f9 100644
--- a/include/linux/resource.h
+++ b/include/linux/resource.h
@@ -80,8 +80,8 @@
 struct task_struct;
 
 int getrusage(struct task_struct *p, int who, struct rusage __user *ru);
-int do_setrlimit(struct task_struct *tsk, unsigned int resource,
-		struct rlimit *new_rlim);
+int do_prlimit(struct task_struct *tsk, unsigned int resource,
+		struct rlimit *new_rlim, struct rlimit *old_rlim);
 
 #endif /* __KERNEL__ */