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A file cloned with "cp --reflink" different from the original one?

From: Jian Lin
Subject: A file cloned with "cp --reflink" different from the original one?
Date: Mon, 23 Nov 2009 18:08:56 +0800

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?


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# cat /proc/filesystems | grep btrfs

address@hidden:/mnt# mount | grep btrfs
/dev/sda4 on /mnt type btrfs (rw)

address@hidden:/mnt# cp --version
cp (GNU coreutils) 8.1
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Torbjorn Granlund, David MacKenzie, and Jim Meyering.

address@hidden:/mnt# cp linjian-test-1-x86 linjian-test-1-x86-ref -R --reflink

address@hidden:/mnt# ls -la linjian-test-1-x86/* linjian-test-1-x86-ref/*
-rw------- 1 root root 419430400 Oct 10 14:21
-rwxr-xr-x 1 root root      1297 Oct 10 14:21
-rw------- 1 root root 419430400 Nov 23 14:59
-rwxr-xr-x 1 root root      1297 Nov 23 14:59

address@hidden:/mnt# md5sum linjian-test-1-x86/* linjian-test-1-x86-ref/*
c34b30f94d220d38e7bfcd2ff6a36f46  linjian-test-1-x86/linjian-test-1-x86.vmdk
64841a05c4112aebec9c25d6d4daecdc  linjian-test-1-x86/linjian-test-1-x86.vmx
2eedfae0f1381de1525ab10eae56d032  linjian-test-1-x86-ref/linjian-test-1-x86.vmdk
64841a05c4112aebec9c25d6d4daecdc  linjian-test-1-x86-ref/linjian-test-1-x86.vmx

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

Jian LIN

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