drbd: Fix adding of new minors with freshly created meta data

Online adding of new minors with freshly created meta data
to an resource with an established connection failed, with a
wrong state transition on one side on one side of the new minor.

Freshly created meta-data has a la_size (last agreed size) of 0.
When we online add such devices, the code wrongly got into
the code path for resyncing new storage that was added while
the disk was detached.

Fixed that by making the GREW from ZERO a special case.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/drbd/drbd_int.h

@@ -1474,7 +1474,8 @@ enum determine_dev_size {
 	DS_ERROR = -1,
 	DS_UNCHANGED = 0,
 	DS_SHRUNK = 1,
-	DS_GREW = 2
+	DS_GREW = 2,
+	DS_GREW_FROM_ZERO = 3,
 };
 extern enum determine_dev_size
 drbd_determine_dev_size(struct drbd_conf *, enum dds_flags, struct resize_parms *) __must_hold(local);

drivers/block/drbd/drbd_nl.c

@@ -955,7 +955,7 @@ drbd_determine_dev_size(struct drbd_conf *mdev, enum dds_flags flags, struct res
 	}
 
 	if (size > la_size_sect)
-		rv = DS_GREW;
+		rv = la_size_sect ? DS_GREW : DS_GREW_FROM_ZERO;
 	if (size < la_size_sect)
 		rv = DS_SHRUNK;