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

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