zab
count_block(dsl_scan_t *scn, zfs_all_blkstats_t *zab, const blkptr_t *bp)
if (zab == NULL)
mutex_enter(&zab->zab_lock);
zfs_blkstat_t *zb = &zab->zab_type[l][t];
mutex_exit(&zab->zab_lock);