dsl_pool_adjustedsize
uint64_t poolsize = dsl_pool_adjustedsize(dd->dd_pool,
avail = dsl_pool_adjustedsize(dd->dd_pool,
uint64_t poolsize = dsl_pool_adjustedsize(dp, slop_policy);
uint64_t dsl_pool_adjustedsize(dsl_pool_t *dp, zfs_space_check_t slop_policy);