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, 11 insertions, 3 deletions

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index b1bcd36ca963..958865445f06 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -212,7 +212,7 @@ static void bitmap_checkfree(struct bitmap *bitmap, unsigned long page)
  */
 
 /* IO operations when bitmap is stored near all superblocks */
-static struct page *read_sb_page(mddev_t *mddev, long offset,
+static struct page *read_sb_page(mddev_t *mddev, loff_t offset,
                                  struct page *page,
                                  unsigned long index, int size)
 {
@@ -287,14 +287,22 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 
         while ((rdev = next_active_rdev(rdev, mddev)) != NULL) {
                         int size = PAGE_SIZE;
-                        long offset = mddev->bitmap_info.offset;
+                        loff_t offset = mddev->bitmap_info.offset;
                         if (page->index == bitmap->file_pages-1)
                                 size = roundup(bitmap->last_page_size,
                                                bdev_logical_block_size(rdev->bdev));
                         /* Just make sure we aren't corrupting data or
                          * metadata
                          */
-                        if (offset < 0) {
+                        if (mddev->external) {
+                                /* Bitmap could be anywhere. */
+                                if (rdev->sb_start + offset + (page->index *(PAGE_SIZE/512)) >
+                                    rdev->data_offset &&
+                                    rdev->sb_start + offset < 
+                                    rdev->data_offset + mddev->dev_sectors +
+                                    (PAGE_SIZE/512))
+                                        goto bad_alignment;
+                        } else if (offset < 0) {
                                 /* DATA  BITMAP METADATA  */
                                 if (offset
                                     + (long)(page->index * (PAGE_SIZE/512))