Date: Thu, 4 Aug 2011 12:03:44 -0400
To: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Cc: Chuck Lever <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org,
        Trond.Myklebust@netapp.com
Subject: Re: State of NFSv4 VolatileFilehandles
Message-ID: <20110804160344.GC12445@fieldses.org>
References: <4E37E66D.90102@linux.vnet.ibm.com>
 <45F4FC20-ED44-4430-A5A9-E06459A194F3@oracle.com>
 <4E38F894.4070003@linux.vnet.ibm.com>
 <2DD1BC2B-6113-4D00-9DD4-C5D431EA1F8A@oracle.com>
 <4E3A8225.1020309@linux.vnet.ibm.com>
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In-Reply-To: <4E3A8225.1020309@linux.vnet.ibm.com>
From: "J. Bruce Fields" <bfields@fieldses.org>
Sender: linux-nfs-owner@vger.kernel.org
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On Thu, Aug 04, 2011 at 04:27:33AM -0700, Venkateswararao Jujjuri wrote:
> One of the usecase is rsync between two physical filesystems; but in
> this particular use case the export
> is readonly (rootfs).  As trond mentioned Volatile FHs are fine in
> the case of readonly exports.
> Is it something we can consider for upstream? VFH only for readonly
> exports.?

The client has no way of knowing that an export is read only.  (Or that
the server guarantees the safety of looking up names again in the more
general cases Neil describes.)  Unless we decide that a server is making
an implicit guarantee of that just by exposing volatile filehandles at
all.  Doesn't sound like the existing spec really says that, though.

If an examination of existing implementations and/or some sort of new
spec language could reassure us that servers will only ever expose
volatile filehandles when it's safe to do so, then maybe it would make
sense for the client to implement volatile filehandle recovery?

But if there's a chance of "unsafe" servers out there, then it would
seem like a trap for the unwary user....

Your rootfs's probably aren't terribly large--could you copy around
compressed block-level images instead of doing rsync?

--b.