netdev - Re: [PATCH v6 3/3] NFSD: add write

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Date: Fri, 26 Jan 2024 18:27:27 +1100
From: "NeilBrown" <neilb@...e.de>
To: "Chuck Lever III" <chuck.lever@...cle.com>
Cc: "Jeff Layton" <jlayton@...nel.org>,
 "Lorenzo Bianconi" <lorenzo@...nel.org>,
 "Linux NFS Mailing List" <linux-nfs@...r.kernel.org>,
 "Lorenzo Bianconi" <lorenzo.bianconi@...hat.com>,
 "Jakub Kicinski" <kuba@...nel.org>, "Simon Horman" <horms@...nel.org>,
 "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>
Subject: Re: [PATCH v6 3/3] NFSD: add write_ports to netlink command

On Fri, 26 Jan 2024, Chuck Lever III wrote:
> 
> 
> > On Jan 25, 2024, at 5:44 PM, NeilBrown <neilb@...e.de> wrote:
> > 
> > On Thu, 25 Jan 2024, Chuck Lever III wrote:
> >> 
> >> 
> >>> On Jan 24, 2024, at 6:24 AM, Jeff Layton <jlayton@...nel.org> wrote:
> >>> 
> >>> On Wed, 2024-01-24 at 10:52 +0100, Lorenzo Bianconi wrote:
> >>>> [...]
> >>>>> 
> >>>>> That's a great question. We do need to properly support the -H option to
> >>>>> rpc.nfsd. What we do today is look up the hostname or address using
> >>>>> getaddrinfo, and then open a listening socket for that address and then
> >>>>> pass that fd down to the kernel, which I think then takes the socket and
> >>>>> sticks it on sv_permsocks.
> >>>>> 
> >>>>> All of that seems a bit klunky. Ideally, I'd say the best thing would be
> >>>>> to allow userland to pass the sockaddr we look up directly via netlink,
> >>>>> and then let the kernel open the socket. That will probably mean
> >>>>> refactoring some of the svc_xprt_create machinery to take a sockaddr,
> >>>>> but I don't think it looks too hard to do.
> >>>> 
> >>>> Do we already have a specific use case for it? I think we can even add it
> >>>> later when we have a defined use case for it on top of the current series.
> >>>> 
> >>> 
> >>> Yes:
> >>> 
> >>> rpc.nfsd -H makes nfsd listen on a particular address and port. By
> >>> passing down the sockaddr instead of an already-opened socket
> >>> descriptor, we can achieve the goal without having to open sockets in
> >>> userland.
> >> 
> >> Tearing down a listener that was created that way would be a
> >> use case for:
> > 
> > Only if it was actually useful.
> > Have you *ever* wanted to do that?  Or heard from anyone else who did?
> 
> Container shutdown will want to clear out any listener
> that might have been created during the container's
> lifetime. How is that done today? Is that simply handled
> by net namespace tear-down?

Yes.  When the last thread in a netns exits, nfsd_last_thread() is
called which closes all sockets.

NeilBrown