md: add possibility to change data-offset for devices.

When reshaping we can avoid costly intermediate backup by
changing the 'start' address of the array on the device
(if there is enough room).

So as a first step, allow such a change to be requested
through sysfs, and recorded in v1.x metadata.

(As we didn't previous check that all 'pad' fields were zero,
 we need a new FEATURE flag for this.
 A (belatedly) check that all remaining 'pad' fields are
 zero to avoid a repeat of this)

The new data offset must be requested separately for each device.
This allows each to have a different change in the data offset.
This is not likely to be used often but as data_offset can be
set per-device, new_data_offset should be too.

This patch also removes the 'acknowledged' arg to rdev_set_badblocks as
it is never used and never will be.  At the same time we add a new
arg ('in_new') which is currently always zero but will be used more
soon.

When a reshape finishes we will need to update the data_offset
and rdev->sectors.  So provide an exported function to do that.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 8 insertions, 2 deletions

diff --git a/include/linux/raid/md_p.h b/include/linux/raid/md_p.h
index 07e05f92d050..ee753536ab70 100644
--- a/include/linux/raid/md_p.h
+++ b/include/linux/raid/md_p.h
@@ -233,7 +233,10 @@ struct mdp_superblock_1 {
         __le32  delta_disks;    /* change in number of raid_disks               */
         __le32  new_layout;     /* new layout                                   */
         __le32  new_chunk;      /* new chunk size (512byte sectors)             */
-        __u8    pad1[128-124];  /* set to 0 when written */
+        __le32  new_offset;     /* signed number to add to data_offset in new
+                                 * layout.  0 == no-change.  This can be
+                                 * different on each device in the array.
+                                 */
 
         /* constant this-device information - 64 bytes */
         __le64  data_offset;    /* sector start of data, often 0 */
@@ -285,11 +288,14 @@ struct mdp_superblock_1 {
                                             * of devices, but is going
                                             * backwards anyway.
                                             */
+#define MD_FEATURE_NEW_OFFSET           64 /* new_offset must be honoured */
 #define MD_FEATURE_ALL                  (MD_FEATURE_BITMAP_OFFSET       \
                                         |MD_FEATURE_RECOVERY_OFFSET     \
                                         |MD_FEATURE_RESHAPE_ACTIVE      \
                                         |MD_FEATURE_BAD_BLOCKS          \
                                         |MD_FEATURE_REPLACEMENT         \
-                                        |MD_FEATURE_RESHAPE_BACKWARDS)
+                                        |MD_FEATURE_RESHAPE_BACKWARDS   \
+                                        |MD_FEATURE_NEW_OFFSET          \
+                                        )
 
 #endif