Date: Fri, 25 Oct 2013 07:43:16 -0400
From: Jeff Layton <jlayton@redhat.com>
To: Steve Dickson <SteveD@redhat.com>
Cc: Linux NFS Mailing list <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH 0/3] mountd: disabling turning off TCP listeners (v2)
Message-ID: <20131025074316.2affe9e9@tlielax.poochiereds.net>
In-Reply-To: <526978BF.7020202@RedHat.com>
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On Thu, 24 Oct 2013 15:45:03 -0400
Steve Dickson <SteveD@redhat.com> wrote:

> 
> 
> On 24/10/13 14:45, Jeff Layton wrote:
> > On Thu, 24 Oct 2013 14:17:10 -0400
> > Steve Dickson <steved@redhat.com> wrote:
> > 
> >> [ Here is the second try for these patches incorporating the code review..]
> >>
> >> Recently it was pointed out to me that the [-n | --no-tcp] flags 
> >> were broken in mountd. Sure enough they are and they broke 
> >> when nfs-utils moved to using libtirpc, which was years ago.
> >>
> >> Obviously nobody is using these flags since has not been 
> >> notice until now, but it seemed to me it no longer makes 
> >> any sense to have flags. We really want people to use TCP 
> >> so why should there be a way to turn it off? It should be
> >> the opposite... They should be able to turn off UDP listeners
> >> not TCP... 
> >>
> >>
> >> Steve Dickson (3):
> >>   mountd: Use protocol bit fields to turn protocols off.
> >>   mountd: Deprecate the ability to disable TCP listeners.
> >>   mountd: Add the ability to disable UDP listeners.
> >>
> >>  support/include/rpcmisc.h |  2 +-
> >>  support/nfs/rpcmisc.c     | 19 ++++++++++++++-----
> >>  support/nfs/svc_create.c  |  5 +++++
> >>  utils/mountd/mountd.c     | 17 ++++++++++++-----
> >>  utils/mountd/mountd.man   |  6 +++---
> >>  5 files changed, 35 insertions(+), 14 deletions(-)
> >>
> > 
> > Sorry I'm coming in late on this...
> np... I was expecting more push back! ;-) 
> 
> > 
> > I don't think we want to remove the ability to disable TCP listeners.
> > 
> > Why, you ask? We've been on a multi-year effort to move people to
> > NFSv4, and with that, there's no reason to have mountd listen on the
> > network at all.
> True...
> 
> > 
> > So personally, I think it would make sense to:
> > 
> > a) allow people to disable listening on UDP in addition to TCP
> I see no reason whatsoever to turn off TCP listeners especially
> since that is the protocol of choice... something we have 
> be spouting about for years...  
>  

There are reasons to be able to turn off TCP listeners:

If you're running a NFSv4-only server, there's no reason to allow it to
listen on TCP _or_ UDP sockets. I think that sort of environment is
going to become more prevalent in the future, not less.

> > 
> > ...or...
> > 
> > b) add an option that prevents it from listening on any sockets for a
> >    v4-only configuration
> In this case it would optimal to not even start mountd, unfortunately
> due to exports reasons, it not possible... but it should be!! :-) 
>   

Right, mountd has 2 jobs:

1) respond to MNT protocol requests from clients

...and...

2) feed exports info to the kernel

For v4, you obviously don't need the first role, so being able to
disable network listeners is a good thing in such a configuration.

> > 
> > In addition, we generally do want people to use UDP for the MNT
> > protocol because it's less apt to cause issues with reserved port
> > exhaustion. Given that it'll continue to listen on a UDP socket by
> > default, that last point is less of an issue, but that might be a good
> > reason to rethink this whole plan.
> > 
> I did think of this.... UDP is on by default... Is up the admin... 
> 

That's good. I have no objection to adding an option to disable UDP
listeners if the admin chooses. I just think it would be best to fix
the ability to disable TCP listeners as well instead of removing it.

-- 
Jeff Layton <jlayton@redhat.com>