md: separate meta and data devs

Allow the metadata to be on a separate device from the
data.

This doesn't mean the data and metadata will by on separate
physical devices - it simply gives device-mapper and userspace
tools more flexibility.

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

1 files changed, 5 insertions, 1 deletions

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 1977765ff964..6cf587196b99 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -264,14 +264,18 @@ static mdk_rdev_t *next_active_rdev(mdk_rdev_t *rdev, mddev_t *mddev)
 static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 {
         mdk_rdev_t *rdev = NULL;
+        struct block_device *bdev;
         mddev_t *mddev = bitmap->mddev;
 
         while ((rdev = next_active_rdev(rdev, mddev)) != NULL) {
                 int size = PAGE_SIZE;
                 loff_t offset = mddev->bitmap_info.offset;
+
+                bdev = (rdev->meta_bdev) ? rdev->meta_bdev : rdev->bdev;
+
                 if (page->index == bitmap->file_pages-1)
                         size = roundup(bitmap->last_page_size,
-                                       bdev_logical_block_size(rdev->bdev));
+                                       bdev_logical_block_size(bdev));
                 /* Just make sure we aren't corrupting data or
                  * metadata
                  */