sf_abytes
sbp->f_bavail = sfp->sf_abytes / NFS_FABLKSIZE;
sbp->sf_abytes = fxdr_hyper(tl); tl += 2;
sfp->sf_abytes != fxdr_hyper(tl))
sfp->sf_abytes = fxdr_hyper(tl);
txdr_hyper(tval, &sfp->sf_abytes);
tquad = fxdr_hyper(&sfp->sf_abytes);