+static void zero_callback(int read_err, unsigned long write_err, void *context)
+{
+ struct bio *bio = context;
+ struct dm_snapshot *s = bio->bi_private;
+
+ up(&s->cow_count);
+ bio->bi_status = write_err ? BLK_STS_IOERR : 0;
+ bio_endio(bio);
+}
+
+static void zero_exception(struct dm_snapshot *s, struct dm_exception *e,
+ struct bio *bio, chunk_t chunk)
+{
+ struct dm_io_region dest;
+
+ dest.bdev = s->cow->bdev;
+ dest.sector = bio->bi_iter.bi_sector;
+ dest.count = s->store->chunk_size;
+
+ down(&s->cow_count);
+ WARN_ON_ONCE(bio->bi_private);
+ bio->bi_private = s;
+ dm_kcopyd_zero(s->kcopyd_client, 1, &dest, 0, zero_callback, bio);
+}
+
+static bool io_overlaps_chunk(struct dm_snapshot *s, struct bio *bio)
+{
+ return bio->bi_iter.bi_size ==
+ (s->store->chunk_size << SECTOR_SHIFT);
+}
+