md: Support write-intent bitmaps with externally managed metadata.

In this case, the metadata needs to not be in the same
sector as the bitmap.
md will not read/write any bitmap metadata.  Config must be
done via sysfs and when a recovery makes the array non-degraded
again, writing 'true' to 'bitmap/can_clear' will allow bits in
the bitmap to be cleared again.

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

1 files changed, 1 insertions, 10 deletions

diff --git a/drivers/md/bitmap.h b/drivers/md/bitmap.h
index 50ee4240f5db..cb821d76d1b4 100644
--- a/drivers/md/bitmap.h
+++ b/drivers/md/bitmap.h
@@ -118,16 +118,6 @@ typedef __u16 bitmap_counter_t;
                         (CHUNK_BLOCK_SHIFT(bitmap) + PAGE_COUNTER_SHIFT - 1)
 #define PAGEPTR_BLOCK_MASK(bitmap) (PAGEPTR_BLOCK_RATIO(bitmap) - 1)
 
-/*
- * on-disk bitmap:
- *
- * Use one bit per "chunk" (block set). We do the disk I/O on the bitmap
- * file a page at a time. There's a superblock at the start of the file.
- */
-
-/* map chunks (bits) to file pages - offset by the size of the superblock */
-#define CHUNK_BIT_OFFSET(chunk) ((chunk) + (sizeof(bitmap_super_t) << 3))
-
 #endif
 
 /*
@@ -250,6 +240,7 @@ struct bitmap {
         wait_queue_head_t write_wait;
         wait_queue_head_t overflow_wait;
 
+        struct sysfs_dirent *sysfs_can_clear;
 };
 
 /* the bitmap API */