ddt_lookup
dde = ddt_lookup(ddt, bp, B_FALSE);
VERIFY(ddt_lookup(ddt, &blk, B_TRUE) != NULL);
extern ddt_entry_t *ddt_lookup(ddt_t *ddt, const blkptr_t *bp, boolean_t add);
dde = ddt_lookup(ddt, bp, B_TRUE);
freedde = dde = ddt_lookup(ddt, bp, B_TRUE);