md: support bitmap offset appropriate for external-metadata arrays.

For md arrays were metadata is managed externally, the kernel does not
know about a superblock so the superblock offset is 0.
If we want to have a write-intent-bitmap near the end of the
devices of such an array, we should support sector_t sized offset.
We need offset be possibly negative for when the bitmap is before
the metadata, so use loff_t instead.

Also add sanity check that bitmap does not overlap with data.

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

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/md/md.h b/drivers/md/md.h
index 4b07e0ab3841..df692953a12f 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -282,11 +282,13 @@ struct mddev_s
         struct bitmap                   *bitmap; /* the bitmap for the device */
         struct {
                 struct file             *file; /* the bitmap file */
-                long                    offset; /* offset from superblock of
+                loff_t                  offset; /* offset from superblock of
                                                  * start of bitmap. May be
                                                  * negative, but not '0'
+                                                 * For external metadata, offset
+                                                 * from start of device. 
                                                  */
-                long                    default_offset; /* this is the offset to use when
+                loff_t                  default_offset; /* this is the offset to use when
                                                          * hot-adding a bitmap.  It should
                                                          * eventually be settable by sysfs.
                                                          */