Re: [LSF/MM/BPF TOPIC] Namespace-aware upcalls from kernel filesystems

On Sat, Feb 14, 2026 at 9:10 PM Chuck Lever <[email protected]> wrote:
>
>
> On Sat, Feb 14, 2026, at 5:06 AM, Shyam Prasad N wrote:
> > Kernel filesystems sometimes need to upcall to userspace to get some
> > work done, which cannot be achieved in kernel code (or rather it is
> > better to be done in userspace). Some examples are DNS resolutions,
> > user authentication, ID mapping etc.
> >
> > Filesystems like SMB and NFS clients use the kernel keys subsystem for
> > some of these, which has an upcall facility that can exec a binary in
> > userspace. However, this upcall mechanism is not namespace aware and
> > upcalls to the host namespaces (namespaces of the init process).
>
> Hello Shyam, we've been introducing netlink control interfaces, which
> are namespace-aware. The kernel TLS handshake mechanism now uses
> this approach, as does the new NFSD netlink protocol.
>
>
> --
> Chuck Lever

Hi Chuck,

Interesting. Let me explore this a bit more.
I'm assuming that this is the file that I should be looking into:
fs/nfsd/nfsctl.c
And that there would be a corresponding handler in nfs-utils?

-- 
Regards,
Shyam