From: Hannes Reinecke <hare@suse.de>
Subject: Switch device-mapper tables to READ-WRITE
References: bnc#440959

Switching a device-mapper table to READ-ONLY works quite well, but
we can't switch back to READ-WRITE as this change will be masked out.
So get rid of this masking and use the flags directly.
And implement a fallback to automatically switch to read-only.

Signed-off-by: Hannes Reinecke <hare@suse.de>

--- linux-2.6.27/drivers/md/dm-table.c.orig	2009-02-02 13:09:06.000000000 +0100
+++ linux-2.6.27/drivers/md/dm-table.c	2009-02-02 14:03:03.000000000 +0100
@@ -423,9 +423,13 @@ static int upgrade_mode(struct dm_dev *d
 
 	dd_copy = *dd;
 
-	dd->mode |= new_mode;
+	dd->mode = new_mode;
 	dd->bdev = NULL;
 	r = open_dev(dd, dev, md);
+	if (r == -EROFS) {
+		dd->mode &= ~FMODE_WRITE;
+		r = open_dev(dd, dev, md);
+	}
 	if (!r)
 		close_dev(&dd_copy, md);
 	else
@@ -487,7 +491,7 @@ static int __table_get_device(struct dm_
 		atomic_set(&dd->count, 0);
 		list_add(&dd->list, &t->devices);
 
-	} else if (dd->mode != (mode | dd->mode)) {
+	} else if (dd->mode != mode) {
 		r = upgrade_mode(dd, mode, t->md);
 		if (r)
 			return r;