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

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Message-Id: <CA140AD1-B715-46BF-81B3-EA2069CBC131@dilger.ca>
Date:	Sun, 2 Oct 2011 01:02:04 -0700
From:	Andreas Dilger <aedilger@...il.com>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	Jeff liu <jeff.liu@...cle.com>, Ted Ts'o <tytso@....edu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [BUG] copy file result with zero

On 2011-10-01, at 11:41 PM, Jeff liu wrote:
>> On Sat, Oct 1, 2011 at 10:39 PM, Ted Ts'o <tytso@....edu> wrote:
>>> On Sat, Oct 01, 2011 at 10:01:35PM +0800, Dave Young wrote:
>>>> 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.
> 
> Actually, upstream cp(1) using FIEMAP only if the source file is sparse,  or else, it will do normal copy, i.e, block based.

Are there any distros that are shipping with a version of cp that depends on FIEMAP?  That would dramatically increase the severity of this problem, since orders of magnitude more users will hit the problem.

Dave, what distro were you seeing this problem on, and had you installed/upgraded your coreutils and/or kernel yourself?

>> Do you means It should work in 3.1.0-rc6 even with cp which depends fiemap?
>> 
>>> 
>>>> 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...
>> 
>> Yes, it works
>> 
>>> 
>>> My suggestion is to upgrade to a newer version of coreutils that
>>> doesn't try to use FIEMAP.
>> 
>> Thanks, will try
>> 
>>> 
>>>                                       - Ted
>>> 
>> 
>> 
>> 
>> -- 
>> Regards
>> Dave
>> --
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> 
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Cheers, Andreas





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