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

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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>
This commit is contained in:
NeilBrown
2009-12-14 12:49:56 +11:00
parent 624ce4f565
commit ece5cff0da
4 changed files with 137 additions and 33 deletions
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11
drivers/md/bitmap.h
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@@ -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 */