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Re: A file cloned with "cp --reflink" different from the original one?
From: |
Pádraig Brady |
Subject: |
Re: A file cloned with "cp --reflink" different from the original one? |
Date: |
Mon, 23 Nov 2009 13:36:01 +0000 |
User-agent: |
Thunderbird 2.0.0.6 (X11/20071008) |
Jian Lin wrote:
> I installed BtrFS 0.19 and GNU coreutils 8.1 on my Ubuntu 9.10.
> I tried to clone some files with "cp --reflink" to make them "copy-on-write".
> However, I found some of the files cloned have different MD5s to the
> original one.
>
> Is BtrFS (or cp with reflink) buggy?
> Or it is indeed a feature that I used incorrectly?
>
> Thanks!
>
> address@hidden:/mnt# uname -a
> Linux lj-laptop 2.6.31-15-generic #50-Ubuntu SMP Tue Nov 10 14:54:29
> UTC 2009 i686 GNU/Linux
>
> address@hidden:/mnt# mount | grep btrfs
> /dev/sda4 on /mnt type btrfs (rw)
>
> address@hidden:/mnt# cp --version
> cp (GNU coreutils) 8.1
>
> address@hidden:/mnt# cd WinXP_CHS/
> address@hidden:/mnt/WinXP_CHS# cp WinXP_CHS.vmdk WinXP_CHS-ref.vmdk --reflink
>
> address@hidden:/mnt/WinXP_CHS# ls -la WinXP_CHS.vmdk WinXP_CHS-ref.vmdk
> -rwxr-xr-x 1 root root 1713766400 Nov 23 15:11 WinXP_CHS-ref.vmdk
> -rwxr-xr-x 1 root root 1713766400 Nov 23 13:32 WinXP_CHS.vmdk
>
> address@hidden:/mnt/WinXP_CHS# md5sum WinXP_CHS.vmdk WinXP_CHS-ref.vmdk
> f6da592d056167a44b089d70fa46f863 WinXP_CHS.vmdk
> e3ee0c2c17771811c80eed088c20987d WinXP_CHS-ref.vmdk
Yikes. Are you 100% sure nothing is changing those vm files?
Note I wouldn't 100% trust the mtime, so an md5sum before
and after would be good to confirm.
You could try this simple prog to do the clones to
implicate coreutils or otherwise:
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#define BTRFS_IOC_CLONE 1074041865
int main(int argc, const char **argv)
{
int in = open(argv[1], O_RDONLY);
int out = open(argv[2], O_CREAT|O_TRUNC|O_WRONLY, 0644);
if (ioctl(out, BTRFS_IOC_CLONE, in)==-1) {
fprintf(stderr, "ioctl error = %m\n");
}
close(in);
close(out);
return 0;
}
cheers,
Pádraig.