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dm exception store: add merge specific methods

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Add functions that decide how many consecutive chunks of snapshot to
merge back into the origin next and to update the metadata afterwards.

prepare_merge provides a pointer to the most recent still-to-be-merged
chunk and returns how many previous ones are consecutive and can be
processed together.

commit_merge removes the nr_merged most-recent chunks permanently from
the exception store.  The number must not exceed that returned by
prepare_merge.

Introduce NUM_SNAPSHOT_HDR_CHUNKS to show where the snapshot header
chunk is accounted for.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mikulas Patocka
2009-12-10 23:52:29 +00:00
committed by Alasdair G Kergon
parent 615d1eb9ca
commit 4454a6216f
2 changed files with 129 additions and 2 deletions
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17
drivers/md/dm-exception-store.h
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@@ -74,6 +74,23 @@ struct dm_exception_store_type {
void (*callback) (void *, int success),
void *callback_context);
/*
* Returns 0 if the exception store is empty.
*
* If there are exceptions still to be merged, sets
* *last_old_chunk and *last_new_chunk to the most recent
* still-to-be-merged chunk and returns the number of
* consecutive previous ones.
*/
int (*prepare_merge) (struct dm_exception_store *store,
chunk_t *last_old_chunk, chunk_t *last_new_chunk);
/*
* Clear the last n exceptions.
* nr_merged must be <= the value returned by prepare_merge.
*/
int (*commit_merge) (struct dm_exception_store *store, int nr_merged);
/*
* The snapshot is invalid, note this in the metadata.
*/