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From: "NeilBrown" <neilb@suse.de>
To: "Chuck Lever III" <chuck.lever@oracle.com>
Cc: "Jeff Layton" <jlayton@kernel.org>,
 "Lorenzo Bianconi" <lorenzo@kernel.org>,
 "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>
Subject: Re: [PATCH v6 3/3] NFSD: add write_ports to netlink command
In-reply-to: <DAB30AAE-41F5-4FC5-AA14-E7E06BB389B5@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>,
 <170622264103.21664.16941742935452333478@noble.neil.brown.name>,
 <DAB30AAE-41F5-4FC5-AA14-E7E06BB389B5@oracle.com>
Date: Fri, 26 Jan 2024 18:27:27 +1100
Message-id: <170625404709.21664.1810481700674698939@noble.neil.brown.name>

On Fri, 26 Jan 2024, Chuck Lever III wrote:
>=20
>=20
> > On Jan 25, 2024, at 5:44=E2=80=AFPM, NeilBrown <neilb@suse.de> wrote:
> >=20
> > On Thu, 25 Jan 2024, Chuck Lever III wrote:
> >>=20
> >>=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 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 th=
en
> >>>>> pass that fd down to the kernel, which I think then takes the socket =
and
> >>>>> sticks it on sv_permsocks.
> >>>>>=20
> >>>>> 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 netlin=
k,
> >>>>> 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.
> >>>>=20
> >>>> 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 ser=
ies.
> >>>>=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
> > Only if it was actually useful.
> > Have you *ever* wanted to do that?  Or heard from anyone else who did?
>=20
> 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