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Message-ID: <1345555236.2231.28.camel@iscandar.digidescorp.com>
Subject: Re: [PATCH 0/4] fat: fix ESTALE errors
From: "Steven J. Magnani" <steve@digidescorp.com>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Namjae Jeon <linkinjeon@gmail.com>,
        OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
        Al Viro <viro@zeniv.linux.org.uk>, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, Namjae Jeon <namjae.jeon@samsung.com>
Date: Tue, 21 Aug 2012 08:20:36 -0500
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On Mon, 2012-08-20 at 16:52 -0400, J. Bruce Fields wrote:

> Fo somebody that knows more about fat than me--is there really any hope
> of making it play well with nfs?

I spent a lot of time looking into FAT ESTALE issues and had proposed
something similar to Namjae (https://lkml.org/lkml/2012/7/3/378). In the
discussions and experiments that followed, I eventually came to the
conclusion that the best I could do was make FAT play "better" with NFS
(https://lkml.org/lkml/2012/7/10/252).

If you define "well" as an absence of server-reported ESTALE due purely
to inode/dentry cache eviction I'm skeptical that this is possible in
any way that would be accepted into the mainline kernel. Code that
addresses ESTALE on the client side (https://lkml.org/lkml/2012/8/8/244)
seems to be successful, but since not everyone has control of the client
code there are cases where a server-side solution is desirable. 

There's just no unique way to identify FAT inodes that works across all
the possible scenarios (renames, power cycles, zero-length files,
deletion of an object and creation of another - potentially of a
different type - at the same on-disk position, etc.). Also,  clients are
sensitive to changes in a file handle - any server "reconstitution" of
an evicted inode must result in a NFS file handle that is identical to
the "original" reported to the client, or the client will cry ESTALE
despite the server's best efforts.

------------------------------------------------------------------------
Steven J. Magnani               "I claim this network for MARS!
www.digidescorp.com              Earthling, return my space modulator!"

#include <standard.disclaimer>


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