On Tue, Oct 11, 2016 at 09:18:11PM -0700, Matthew Ahrens wrote:
> I'm not sure, I don't see that restriction in the illumos zfs_ctldir.c.
> This is speculation, but it may be that on linux the inode number of stuff
> in .zfs/snapshot has the high bits set (above bit 32), and that doesn't
> work on 32-bit?

Thanks Matthew,

Yes, the restriction is linux-specific but I got no answer on the
@zfsonlinux list.

My impression is that whoever wrote that code wanted to be cautious
and also avoid the burden of analysis and maintenance for the 32-bit case.

Nevertheless as I wrote I did not find any apparent issues in the code
nor in practice, having built with ctldir enabled (but not heavily tested).

I can think that no developer really cares about the 32-linux platform,
assuming that ZFS is "only" interesting for large storage installations
where one of course picks 64-bit servers.

This unfortunately hurts a non-neglectable usage niche, where we handle
moderate amounts of data on 32-bit kernels but still need the robustness
and the administration advantages of zfs. This may become a reason for
switching to a different kernel, but it would be nice to know whether
the linux limitation is there for real.

(at least, nice that someone was listening here! :)

Best regards,

> On Mon, Sep 26, 2016 at 3:00 AM, <u-r...@aetey.se> wrote:
> > Hope somebody would be willing to describe the details of what will break
> > on a 32-bit linux platform with the .zfs ctldir support enabled.
> > 
> > A brief reading of the code did not reveal to me anything that apparently
> > would become wrong, even though the comment in the file says that the
> > ctldir must be disabled on 32-bit.
> > 
> > Nor does a 32-bit build with ctldir enabled readily crash or corrupt data.
> > 
> > Would anybody who is familiar with the underlying structures explain why
> > it would be hard (or what is needed) to enable the functionality for a
> > 32-bit linux environment?

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