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Message-ID: <55283b0a01d3b3ae2eb965929a6d81256a48b11e.camel@kernel.org>
Subject: Re: [PATCH v6 3/3] NFSD: add write_ports to netlink command
From: Jeff Layton <jlayton@kernel.org>
To: Chuck Lever III <chuck.lever@oracle.com>, Lorenzo Bianconi
	 <lorenzo@kernel.org>, Neil Brown <neilb@suse.de>
Cc: Linux NFS Mailing List <linux-nfs@vger.kernel.org>, Lorenzo Bianconi
 <lorenzo.bianconi@redhat.com>, Jakub Kicinski <kuba@kernel.org>, Simon
 Horman <horms@kernel.org>, "open list:NETWORKING [GENERAL]"
 <netdev@vger.kernel.org>
Date: Wed, 24 Jan 2024 13:10:53 -0500
In-Reply-To: <917EC07C-C9D9-4CF2-9ACB-DCA2676DFF67@oracle.com>
References: <cover.1705771400.git.lorenzo@kernel.org>
	 <f7c42dae2b232b3b06e54ceb3f00725893973e02.1705771400.git.lorenzo@kernel.org>
	 <9e3ae337dcf168c60c4cfd51aa0b2fc7b24bcbfb.camel@kernel.org>
	 <170595930799.23031.17998490973211605470@noble.neil.brown.name>
	 <Za7zHvPJdei/vWm4@tissot.1015granger.net> <Za-N6BxOMXTGyxmW@lore-desk>
	 <85b02061798a1b750a87b0302681b86651d0c7a3.camel@kernel.org>
	 <Za-9P0NjlIsc1PcE@lore-desk>
	 <3f035d3bc494ec03b83ae237e407c42f2ddc4c53.camel@kernel.org>
	 <ZbDdzwvP6-O2zosC@lore-desk>
	 <8fabd83caa0d44369853a4040a89c069f9b0f935.camel@kernel.org>
	 <917EC07C-C9D9-4CF2-9ACB-DCA2676DFF67@oracle.com>
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On Wed, 2024-01-24 at 13:55 +0000, Chuck Lever III wrote:
>=20
> > On Jan 24, 2024, at 6:24=E2=80=AFAM, Jeff Layton <jlayton@kernel.org> w=
rote:
> >=20
> > On Wed, 2024-01-24 at 10:52 +0100, Lorenzo Bianconi wrote:
> > > [...]
> > > >=20
> > > > That's a great question. We do need to properly support the -H opti=
on 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 socke=
t and
> > > > sticks it on sv_permsocks.
> > > >=20
> > > > All of that seems a bit klunky. Ideally, I'd say the best thing wou=
ld be
> > > > to allow userland to pass the sockaddr we look up directly via netl=
ink,
> > > > and then let the kernel open the socket. That will probably mean
> > > > refactoring some of the svc_xprt_create machinery to take a sockadd=
r,
> > > > but I don't think it looks too hard to do.
> > >=20
> > > Do we already have a specific use case for it? I think we can even ad=
d it
> > > later when we have a defined use case for it on top of the current se=
ries.
> > >=20
> >=20
> > Yes:
> >=20
> > 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.
>=20
> Tearing down a listener that was created that way would be a
> use case for:
>=20
> > 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.
>=20

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.=C2=
=A0

It would be a little silly to make userland open a socket in order to
close the one that nfsd is listening on.
--=20
Jeff Layton <jlayton@kernel.org>