amd64/74811: [nfs] df, nfs mount, negative Avail -> 32/64-bit confusion

[Astrodog]

> I cannot see how to get the correct result non-accidentally without
> using the hack of passing negative values as large unsigned ones.
> Passing negative values as the difference of two unsigned values works
> with NetBSD's extension to statvfs (f_bresvd), but it doesn't work for
> nfs because it requires an extra value which the protocol doesn't
> support AFAIK (not far).
>
> Bruce
>

>From the above, it doesn't appear that NFS can support negative
values, in any reasonable way... and I suppose that saying "There are
zero blocks avalible for non-privileged users" is accurate, when
bavail <= 0.

I'm going to dig through the RFCs and see if there's an otherwise
unused or underused variable that could be used to store bresvd, for
clients that could support it.

Thanks for the detailed explaination,
--- Harrison