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

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Date:	Sun, 2 Oct 2011 14:41:07 +0800
From:	Jeff liu <jeff.liu@...cle.com>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	"Ted Ts'o" <tytso@....edu>,
	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 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:
>>> 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.

Actually, upstream cp(1) using FIEMAP only if the source file is sparse,  or else, it will do normal copy, i.e, block based.


Thanks,
-Jeff
> 
> 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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