linux-ext4 - Re: [BUG] copy file result with zero

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Message-ID: <20111001143900.GH28234@thunk.org>
Date:	Sat, 1 Oct 2011 10:39:00 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-ext4@...r.kernel.org
Subject: Re: [BUG] copy file result with zero

On Sat, Oct 01, 2011 at 10:01:35PM +0800, Dave Young wrote:
> Hi,
> 
> Weird problem, when I build app from source,
> make; make install
> run the command, but got "cannot execute binary file"
> 
> hexdump shows the installed binary is full of zero
> 
> Is it related to ext4 fiemap problem described below?
> http://lwn.net/Articles/429349/

There is general agreement that /bin/cp should not have been relying
on FIEMAP, and I believe the more recent versions of /bin/cp have
removed that code by default pending implementation of
SEEK_HOLE/SEEK_DATA.  That being said, ext4 had a workaround to its
FIEMAP implementation that landed in 2.6.39, and you're using
3.1.0-rc6.

> I finally managed to find the way to reproduce this:
> just cp a elf binary A  to file B, then cp B to file C,  then you will get:
> A == B != C
> 
> ie.
> cp /bin/ls ls1
> cp ls1 ls2
> 
> ls2 will be filled with zero

If you add a "sync" between the two copies, does that work around the
problem?  I bet it will...

My suggestion is to upgrade to a newer version of coreutils that
doesn't try to use FIEMAP.

					- Ted
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