linux-kernel - Re: [NFS] blocks of zeros (NULLs) in NFS files in kernels >= 2.6.20

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Date:	Mon, 22 Sep 2008 12:35:22 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Hans-Peter Jansen <hpj@...la.net>
Cc:	linux-kernel@...r.kernel.org, Aaron Straus <aaron@...finllc.com>,
	Chuck Lever <chuck.lever@...cle.com>,
	Neil Brown <neilb@...e.de>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [NFS] blocks of zeros (NULLs) in NFS files in kernels >= 2.6.20

On Mon, 2008-09-22 at 18:05 +0200, Hans-Peter Jansen wrote:
> For what is worth, this behavior is visible in bog standard writing/reading 
> files, (log files in my case, via the python logging package). It obviously 
> deviates from local filesystem behavior, and former state of the linux 
> nfs-client. Should we add patches to less, tail, and all other instruments 
> for watching/analysing log files (just to pick the tip of the ice rock) in 
> order to throw away runs of zeros, when reading from nfs mounted files? Or 
> should we ask their maintainers to add locking code for the nfs "read 
> files, which are written at the same time" case, just to work around 
> __some__ of the consequences of this bug? Imagine, how ugly this is going 
> to look! 
> 
> The whole issue is what I call a major regression, thus I strongly ask for a 
> reply from Trond on this matter.
> 
> I even vote for sending a revert request for this hunk to the stable team, 
> where it is applicable, after Trond sorted it out (for 2.6.27?).
> 
> Thanks, Aaron and Chuck for the detailed analysis - it demystified a wired 
> behavior, I observed here. When you're in a process to get real work done 
> in a fixed timeline, such things could make you mad..

Revert _what_ exactly?

Please assume that I've been travelling for the past 5 weeks, and have
only a sketchy idea of what has been going on.
My understanding was that this is a consequence of unordered writes
causing the file to be extended while some other task is reading.
AFAICS, this sort of behaviour has _always_ been possible. I can't see
how reverting anything will fix it.

  Trond

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