linux-kernel - Re: [PATCH] vfs: pass struct file to do_truncate on O

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Message-ID: <1268692288.3040.2.camel@localhost.localdomain>
Date:	Mon, 15 Mar 2010 18:31:28 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-nfs@...r.kernel.org
Subject: Re: [PATCH] vfs: pass struct file to do_truncate on O_TRUNC opens

On Mon, 2010-03-15 at 17:39 -0400, Jeff Layton wrote: 
> When a file is opened with O_TRUNC, the truncate processing is handled
> by handle_truncate(). This function however doesn't receive any info
> about the newly instantiated filp, and therefore can't pass that info
> along so that the setattr can use it.
> 
> This makes NFSv4 misbehave. The client does an open and gets a valid
> stateid, and then doesn't use that stateid on the subsequent truncate.
> It uses the zero-stateid instead. Most servers ignore this fact and
> just do the truncate anyway, but some don't like it (notably, RHEL4).
> 
> It seems more correct that since we have a fully instantiated file at
> the time that handle_truncate is called, that we pass that along so
> that the truncate operation can properly use it.

At least in the O_CREAT|O_TRUNC case, we really should modify
nfs4_opendata_alloc() to set the attrs.ia_size to zero, so that the
server does an atomic open(O_CREAT|O_TRUNC) for us (see the DESCRIPTION
paragraph in RFC3530 section 14.2.16). There shouldn't be any need for
an extra truncate RPC call.

Plain open(O_TRUNC) probably does need something along the lines of what
you propose, however.

Cheers
  Trond 

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