Re: UFS s_maxbytes bogosity

[Al Viro <viro@ZenIV.linux.org.uk>]

On Sun, Jun 04, 2017 at 12:31:34PM -0700, Linus Torvalds wrote:

> and in particular the patch in there that just makes UFS use MAX_LFS_FILESIZE:
> 
>     https://bugzilla.kernel.org/attachment.cgi?id=256853&action=diff
 
> I'm inclined to just apply it, since clearly the default 2G limit
> isn't appropriate for UFS, although it would perhaps be a good idea to
> figure out just what the true UFS maximum file size can be.. The
> on-disk "ui_size" field seems to be a 64-bit entity, so
> MAX_LFS_FILESIZE is certainly better, but there's probably some index
> tree limit that depends on the block size or whatever.

Depends.  There had been a lot of UFS variants (hell, ext2 is one), so
limits differ.  They are also kernel-dependent.

One hard limit is the same as in ext2 - indirect blocks contain pointers
to blocks, so you get (10 + n + n^2 + n^3)*block_size, where n is
block_size / pointer size.  For UFS pointers are 32bit (UFS2 is trickier,
but we don't support that).

Another pile of fun is VM-related and that varies from kernel to kernel.
FWIW, current FreeBSD has no problems with that (32bit included), but
there had been 4.4BSD variants that used to.