Re: Status of mount.nfs

[Chuck Lever <chuck.lever@oracle.com>]

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Hi Steinar-

Steinar H. Gunderson wrote:
> On Mon, Jul 23, 2007 at 06:13:42PM -0400, Chuck Lever wrote:
>> It would help if we could take a look at a clean network trace of the bad 
>> and the good mount operations.
> 
> It was quite simple to test this myself. I started the kernel server on a
> machine, then shut down portmap. First I did:
> 
>   fugl:~> sudo mount -t nfs -o port=2049,mountport=901,nfsvers=3 192.168.0.101:/ /mnt
>   mount: mount to NFS server '192.168.0.101' failed: System Error: Connection refused.
> 
> The dump is attached as "default.dump". Then I did
> 
>   fugl:~> sudo mount -t nfs -o port=2049,mountport=901,nfsvers=3,udp 192.168.0.101:/ /mnt 
> 
> which is attached as "udp.dump".
> 
> Note that in default.dump, UDP is simply never tried at all. I believe that
> to be a bug.

I'm looking at probe_nfsport() and probe_mntport() and I see that the 
portmapper call is avoided iff the protocol version, transport protocol, 
and the port number are all specified in advance.

So if you specify:

    -o mountport=650,port=2049

mount will still contact the server's portmapper to determine which 
transport protocols are available (and this breaks through a firewall 
that doesn't pass portmapper requests).  Only if you specify:

    -o tcp,mountport=650,port=2049

or

    -o udp,mountport=650,port=2049

then the portmapper calls are avoided entirely.  For some reason 
probe_bothports() sets the default NFS version to 3 but does not set a 
default transport protocol.

The transport protocols are probed differently for NFS and MNT: for MNT, 
UDP is probed first then TCP; for NFS, the opposite is true.  The mount 
command is supposed to try both transport protocol types both for NFS 
and MNT, but it appears that it is failing to try the other type if the 
first fails... I see this is also problematic for umount.nfs.

So yes, I think the logic is there, but it's broken.  I recall that the 
transport protocol probing logic was added recently.

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