pstore: Implement show_options

Implement the show_options superblock op for pstore as part of a bid to get
rid of s_options and generic_show_options() to make it easier to implement
a context-based mount where the mount options can be passed individually
over a file descriptor.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Kees Cook <keescook@chromium.org>
cc: Anton Vorontsov <anton@enomsg.org>
cc: Colin Cross <ccross@android.com>
cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/pstore/internal.h

@@ -5,6 +5,9 @@
 #include <linux/time.h>
 #include <linux/pstore.h>
 
+#define PSTORE_DEFAULT_KMSG_BYTES 10240
+extern unsigned long kmsg_bytes;
+
 #ifdef CONFIG_PSTORE_FTRACE
 extern void pstore_register_ftrace(void);
 extern void pstore_unregister_ftrace(void);