Re: [PATCH - v3] mount.nfs: Fix fallback from tcp to udp

From: NeilBrown <neilb@suse.de>
To: Steve Dickson <steved@redhat.com>
Cc: Linux NFS Mailing list <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH - v3] mount.nfs: Fix fallback from tcp to udp
Date: Wed, 12 Mar 2014 16:55:26 +1100	[thread overview]
Message-ID: <20140312165526.76332207@notabene.brown> (raw)
In-Reply-To: <1394551050-14571-1-git-send-email-steved@redhat.com>

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On Tue, 11 Mar 2014 11:17:30 -0400 Steve Dickson <steved@redhat.com> wrote:

> From: NeilBrown <neilb@suse.de>
> 
> Protocol negotiation in mount.nfs does not correctly negotiate with a
> server which only supports NFSv3 and UDP.
> 
> When mount.nfs attempts an NFSv4 mount and fails with ECONNREFUSED
> it does not fall back to NFSv3, as this is not recognised as a
> "does not support NFSv4" error.
> However ECONNREFUSED is a clear indication that the server doesn't
> support TCP, and ipso facto does not support NFSv4.
> So ECONNREFUSED should trigger a fallback from v4 to v2/3.
> 
> However ECONNREFUSED may simply indicate that NFSv4 isn't supported
> *yet*.  i.e. the server is still booting and isn't responding to NFS
> requests yet.  So if we subsequently find that NFSv3 is supported, we
> need to check with the server to confirm that NFSv4 really isn't
> supported.
> 
> If server reports that v4 is not supported after reporting that v3
> is, we can safely use v4.  If it reports that v4 is supported, we need
> to retry v4.
> 
> Signed-off-by: Steve Dickson <steved@redhat.com>
> Reported-by: Carsten Ziepke <kieltux@gmail.com>
> ---

> +		memcpy(&save_sa, sap, salen);
> +
> +		ret = nfs_probe_port(sap, salen, pmap,
> +				     probe_nfs3_only, probe_proto);
> +		if (!ret || !checkv4 || probe_proto != probe_tcp_first)
> +			return ret;
> +
> +		nfs_set_port((struct sockaddr *)&save_sa, NFS_PORT);
> +		ret =  nfs_rpc_ping((struct sockaddr *)&save_sa, salen, 
> +			NFS_PROGRAM, 4, IPPROTO_TCP, NULL);

That turns out to be very neat, doesn't it?
I'm quite happy with this version instead.

Thanks,
NeilBrown

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