Re: [LSF/MM/BPF TOPIC] Namespace-aware upcalls from kernel filesystems
Shyam Prasad N <[email protected]>
| Newsgroups | org.kernel.vger.keyrings,org.kernel.vger.linux-cifs,org.kernel.vger.linux-fsdevel,org.kernel.vger.linux-nfs |
|---|---|
| Message-ID | <CANT5p=q05gni_jd4=KHsmR0LnF5HE9gNfo17q6f8ngsjY5EZdw@mail.gmail.com> |
On Tue, Feb 17, 2026 at 7:51 PM Chuck Lever <[email protected]> wrote: > > > > On Mon, Feb 16, 2026, at 11:14 PM, Shyam Prasad N wrote: > > 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 > > Yes, clustered towards the end of the file. NFSD's use of netlink > is as a downcall-style administrative control plane. > > net/handshake/netlink.c uses netlink as an upcall for driving > kernel-initiated TLS handshake requests up to a user daemon. This > mechanism has been adopted by NFSD, the NFS client, and the NVMe > over TCP drivers. An in-kernel QUIC implementation is planned and > will also be using this. > > > > And that there would be a corresponding handler in nfs-utils? > > For NFSD, nfs-utils has a new tool called nfsdctl. > > The TLS handshake user space components are in ktls-utils. See: > https://github.com/oracle/ktls-utils > > -- > Chuck Lever Thanks Chuck. Will explore this in more detail. -- Regards, Shyam