64-bit inode number issues

[David Howells <dhowells@redhat.com>]

Christoph Hellwig <hch@infradead.org> wrote:

> 01-ino64.diff:
> 	ACK
> 
> 02-ino64-nfs.diff:
> 	Unfortunately there's a lot of broken userspace that can't deal
> 	with 64bit inode numbers, so you need to make the lod behaviour
> 	a mount option at least, probably even the default.  Given that
> 	we're going to run into problems like that it might make sense
> 	to make the option VFS-level instead of just in nfs.  (Note:
> 	XFS already has an option like that)

This problem doesn't just apply to NFS.  It applies to any filesystem that can
generate 64-bit inode numbers - which includes Ext3, I believe - so not
applying the NFS patch doesn't really solve your problem (Al Viro asked me for
examples of that, btw) and leaves my problem unsolved.

I think any solution has to apply at the VFS level or higher.  I'm not sure Al
agrees though.  I think we have to do one of the following:

 (1) Turn on inode number compression (which tries to hide the problem).

 (2) Give an error to stat and getdents if the inode number can't be
     represented by 32-bits.

And I think we're going to do this, that we need to do this on a per-superblock
basis or on a per-system basis, and I think it should be _off_ by default.  It
might also be possible to do it on a per-process level, but I suspect that'd be
too much effort.

David