lfs_availwait
lfs_availwait(fs, frags);
lfs_availwait(fs, lfs_btofsb(fs, 1 << lfs_sb_getbshift(fs)));
int lfs_availwait(struct lfs *, int);
lfs_availwait(fs, lfs_btofsb(fs, uio->uio_resid));
lfs_availwait(fs, lfs_btofsb(fs, uio->uio_resid));