CRED: Wrap task credential accesses in the filesystem subsystem

Wrap access to task credentials so that they can be separated more easily from
the task_struct during the introduction of COW creds.

Change most current->(|e|s|fs)[ug]id to current_(|e|s|fs)[ug]id().

Change some task->e?[ug]id to task_e?[ug]id().  In some places it makes more
sense to use RCU directly rather than a convenient wrapper; these will be
addressed by later patches.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/fs/fcntl.c b/fs/fcntl.c
index ac4f7db..bf049a8 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -211,7 +211,7 @@
 	if (err)
 		return err;
 
-	f_modown(filp, pid, type, current->uid, current->euid, force);
+	f_modown(filp, pid, type, current_uid(), current_euid(), force);
 	return 0;
 }
 EXPORT_SYMBOL(__f_setown);