[dm-devel] [PATCH] Allow switch device-mapper tables to READ-WRITE

[Nikanth Karthikesan]

From: Hannes Reinecke <hare at suse.de>
Subject: Allow switch device-mapper tables to READ-WRITE

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 at suse.de>
Signed-off-by: Nikanth Karthikesan <knikanth at suse.de>

---

Index: linux-2.6-dm/drivers/md/dm-table.c
===================================================================
--- linux-2.6-dm.orig/drivers/md/dm-table.c
+++ linux-2.6-dm/drivers/md/dm-table.c
@@ -403,10 +403,15 @@ static int upgrade_mode(struct dm_dev_in
 
 	dd_new = dd_old = *dd;
 
-	dd_new.dm_dev.mode |= new_mode;
+	dd_new.dm_dev.mode = new_mode;
 	dd_new.dm_dev.bdev = NULL;
 
 	r = open_dev(&dd_new, dd->dm_dev.bdev->bd_dev, md);
+	if (r == -EROFS) {
+		dd_new.dm_dev.mode &= ~FMODE_WRITE;
+		r = open_dev(&dd_new, dd->dm_dev.bdev->bd_dev, md);
+	}
+
 	if (r)
 		return r;
 
@@ -473,7 +478,7 @@ static int __table_get_device(struct dm_
 		atomic_set(&dd->count, 0);
 		list_add(&dd->list, &t->devices);
 
-	} else if (dd->dm_dev.mode != (mode | dd->dm_dev.mode)) {
+	} else if (dd->dm_dev.mode != mode) {
 		r = upgrade_mode(dd, mode, t->md);
 		if (r)
 			return r;