Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:44945 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932070AbaBUPAA (ORCPT ); Fri, 21 Feb 2014 10:00:00 -0500 Date: Fri, 21 Feb 2014 09:59:56 -0500 From: "J. Bruce Fields" To: NeilBrown Cc: Steve Dickson , Chuck Lever , NFS , Carsten Ziepke Subject: Re: [PATCH - nfs-utils] Fix fallback from tcp to udp Message-ID: <20140221145956.GE13433@fieldses.org> References: <20140218104307.34205fc8@notabene.brown> <53064057.70703@RedHat.com> <20140220203701.GA13433@fieldses.org> <20140221142641.20e72abe@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20140221142641.20e72abe@notabene.brown> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, Feb 21, 2014 at 02:26:41PM +1100, NeilBrown wrote: > On Thu, 20 Feb 2014 15:37:02 -0500 "J. Bruce Fields" > wrote: > > Any NFS server has to support either tcp or rpcbind. But it's OK for a > > server to support only of those two. So the only way to handle both > > cases while continuing to retry after ECONNREFUSED is to alternate > > between trying nfs4/tcp and rpcbind until you can connect to one or the > > other. > > > > If it's the rpcbind call that succeeds first then I think we want to do > > one more try of nfs4/tcp just to make sure it didn't just come up, > > before falling back to v3. > > > > The rpcbind call is done in userspace, if I understand right, so I think > > this is doable. Looking at utils/mount/ I don't understand the mount > > process well enough to understand exactly how to do it. Maybe > > everything but the final nfs_sys_mount needs to be moved out of > > nfs_do_mount_v3v2 into a new nfs_do_probe_v3v2 and nfs_autonegotiate > > should alternate between nfs_try_mount_v4 and nfs_do_probe_v3v2 as long > > as both return ECONNREFUSED, calling nfs_try_mount_v3v2 only if > > nfs_try_mount_v4 has failed after a succesful nfs_do_probe_v3v2? > > > > Except the v3v2 mount logic seems to actually modify the mount_options, > > so probably that doesn't quite work. > > I had come to much the same conclusion after reading Steve's mail: when TCP > fails we need rpcbind to be sure what to do. > I suspect it should be fairly straight forward to implement (I'm less > pessimistic than you). I'll have a go on Monday. OK, great! Yeah, the mount code looked like a maze for me but I probably spent less than an hour trying to trace through it, I'm sure it's not that bad. --b.