Re: [RFC PATCH v2 00/11] NFS/NFSD: nfs4_acl passthru for NFSv4 reexport

Trond Myklebust
2026-03-10T14:53:57Z

On Tue, 2026-03-10 at 06:26 -0700, Christoph Hellwig wrote:
> NAK on this whole thing.  Linux does not support NFSv4 ACLs for
> pretty
> good reasons.  If you want to add it you'd have to do it properly
> (even
> if that is a bad idea in my opinion).  But adding a weird special
> case
> for passthrough is a no-go.  To be honest I really don't understand
> why
> your (as in Hammerspae, not you personally) want to abuse the kernel
> nfsd and nfs client for that.  If you want to pass in the protocol do
> it in userspace without burdening the kernel with it.
>

Like it or not, Linux knfsd _does_ pretend to support NFSv4 ACLs. It
does so by using a (lossy!) mapping to try to convert the NFSv4 ACL
into a POSIX style ACL.
This is a problem when you're re-exporting NFSv4, as we need to do,
because at best it mangles your ACL. At worst, it throws random error
codes back at the client.

So Hammerspace does need that passthrough ACL in order to have re-
exports work as expected.

If the upstream community is unwilling to take patches to address the
issue, then we're quite happy to maintain the code separately. It will
still be available to those who need it through our github site.

--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trondmy@kernel.org, trond.myklebust@hammerspace.com