[PATCH][RFC] dm: Do not open log and cow device read-write for read-only mappings

[Milan Broz <mbroz@redhat.com>]

> But it doesn't fix the read-only snapshot issue and I guess there will be
> the same problem with read-only MD code too.
> (so the 2) issue here https://lkml.org/lkml/2011/2/12/209).
I am not sure if this is complete fix... note that:
- what happens during mirror resync and read-only log?
- for COW, it there situation we need to update header in read-oly mode? (invalidated snap?)
Milan
--

[RFC] Do not open log and cow device read-write for read-only mappings

Signed-off-by: Milan Broz <mbroz@redhat.com> 

diff --git a/drivers/md/dm-log.c b/drivers/md/dm-log.c
index 6951536..8e8a868 100644
--- a/drivers/md/dm-log.c
+++ b/drivers/md/dm-log.c
@@ -543,7 +543,7 @@ static int disk_ctr(struct dm_dirty_log *log, struct dm_target *ti,
 		return -EINVAL;
 	}
 
-	r = dm_get_device(ti, argv[0], FMODE_READ | FMODE_WRITE, &dev);
+	r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &dev);
 	if (r)
 		return r;
 
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index fdde53c..a2d3309 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1080,7 +1080,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	argv++;
 	argc--;
 
-	r = dm_get_device(ti, cow_path, FMODE_READ | FMODE_WRITE, &s->cow);
+	r = dm_get_device(ti, cow_path, dm_table_get_mode(ti->table), &s->cow);
 	if (r) {
 		ti->error = "Cannot get COW device";
 		goto bad_cow;