iostat_alloc
st->stats = iostat_alloc(IOSTAT_TAPE, parent,
diskp->dk_stats = iostat_alloc(IOSTAT_DISK, diskp, diskp->dk_name);
nmp->nm_stats = iostat_alloc(IOSTAT_NFS, nmp, iosname);
struct io_stats *iostat_alloc(int32_t, void *, const char *);