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

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Message-ID: <B85C6ED2-E2F6-4224-883A-E7DAB54EFF09@oracle.com>
Date: Fri, 26 Jan 2024 13:58:24 +0000
From: Chuck Lever III <chuck.lever@...cle.com>
To: Neil Brown <neilb@...e.de>
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 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?

Another possibility is removing a listener when unplugging a
network device. That also might be automatic already.

But hey, we don't have this kind of administrative capability
today, so there's no need to add it in a first pass of this
new interface either. I'm happy to wait and see.


>>> 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.


--
Chuck Lever