md: allow devices to be shared between md arrays

Currently, a given device is "claimed" by a particular array so that it cannot
be used by other arrays.

This is not ideal for DDF and other metadata schemes which have their own
partitioning concept.

So for externally managed metadata, just claim the device for md in general,
require that "offset" and "size" are set properly for each device, and make
sure that if a device is included in different arrays then the active sections
do not overlap.

This involves adding another flag to the rdev which makes it awkward to set
"->flags = 0" to clear certain flags.  So now clear flags explicitly by name
when we want to clear things.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index c77dca3221ed..5b2102e40286 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -81,6 +81,8 @@ struct mdk_rdev_s
 #define In_sync         2               /* device is in_sync with rest of array */
 #define WriteMostly     4               /* Avoid reading if at all possible */
 #define BarriersNotsupp 5               /* BIO_RW_BARRIER is not supported */
+#define AllReserved     6               /* If whole device is reserved for
+                                         * one array */
 
         int desc_nr;                    /* descriptor index in the superblock */
         int raid_disk;                  /* role of device in array */