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

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Message-ID: <55283b0a01d3b3ae2eb965929a6d81256a48b11e.camel@kernel.org>
Date: Wed, 24 Jan 2024 13:10:53 -0500
From: Jeff Layton <jlayton@...nel.org>
To: Chuck Lever III <chuck.lever@...cle.com>, Lorenzo Bianconi
	 <lorenzo@...nel.org>, Neil Brown <neilb@...e.de>
Cc: 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 Wed, 2024-01-24 at 13:55 +0000, 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:
> 
> > Do we ever want/need to remove listening sockets?
> > Normal practice when making any changes is to stop and restart where
> > "stop" removes all sockets, unexports all filesystems, disables all
> > versions.
> 

Good point. Even if we don't want to allow it today, passing down a
sockaddr over netlink gives us an interface to properly match a
listening socket for shutting them down without taking down the server. 

It would be a little silly to make userland open a socket in order to
close the one that nfsd is listening on.
-- 
Jeff Layton <jlayton@...nel.org>