Make fraction_full() return a percentage of the amount of actual data
the device can hold, rather than of the amount of data+metadata it can
hold.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
---
drivers/md/dm-exception-store.c | 36 ++++++++++++++++++++++++++++++++++--
1 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-exception-store.c b/drivers/md/dm-exception-store.c
index 5bbce29..02fd3e9 100644
--- a/drivers/md/dm-exception-store.c
+++ b/drivers/md/dm-exception-store.c
@@ -429,11 +429,43 @@ static struct pstore *get_info(struct exception_store *store)
return (struct pstore *) store->context;
}

+/*
+ * Calculate the number of chunks of data we can store in @n_chunks,
+ * given that each metadata area can store @exceptions_per_area
+ * exceptions.
+ */
+static inline uint32_t calc_n_data_chunks(uint32_t n_chunks,
+ uint32_t exceptions_per_area)
+{
+ uint32_t stride, full_areas, leftovers;
+
+ /* we can't use the header */
+ if (--n_chunks <= 0)
+ return 0;
+
+ stride = exceptions_per_area + 1;
+
+ /* how many metadata areas would we completely fill? */
+ full_areas = n_chunks / stride;
+
+ /* how many chunks could we fit after the full areas? */
+ leftovers = n_chunks % stride;
+ if (leftovers - 1 <= 0)
+ leftovers = 0;
+
+ return (full_areas * exceptions_per_area) + leftovers;
+}
+
static void persistent_fraction_full(struct exception_store *store,
sector_t *numerator, sector_t *denominator)
{
- *numerator = get_info(store)->next_free * store->snap->chunk_size;
- *denominator = get_dev_size(store->snap->cow->bdev);
+ struct pstore *ps = get_info(store);
+ uint32_t n_chunks;
+
+ n_chunks = get_dev_size(ps->snap->cow->bdev) >> ps->snap->chunk_shift;
+
+ *numerator = calc_n_data_chunks(ps->next_free, ps->exceptions_per_area);
+ *denominator = calc_n_data_chunks(n_chunks, ps->exceptions_per_area);
}

static void persistent_destroy(struct exception_store *store)
--
1.5.4.1

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