mv fails to preserve COW on btrfs

[Charlie Todd]

the /bin/mv command fails to preserve extended attributes, specifically the COW (lsattr; chattr +C) on btrfs, for both files and directories. Affects virtual machine images in VirtualBox which perform POORLY if hosted on btrfs without COW set.

Workaround:
1. Set the folder to have the COW flag (chattr +C .)
2. Back up all of the files (for c in *; do mv $c $c.old; done)
3. Copy the files to the same folder, assuming that there is space, and delete the backup upon success (for c in $.old; do cp $c ${c/.old/} && rm $c)

User has to copy the file to a COW flagged directory before VirtualBox will talk correctly to the block device images.

coreutils, 8.21-1ubuntu5, amd64
btrfs-tools, 3.12-1, amd64
kernel 3.13.0-32-generic

Filesystem was created under Trusty (14.04.1 LTS).

$ apt-cache policy coreutils
coreutils:
  Installed: 8.21-1ubuntu5
  Candidate: 8.21-1ubuntu5
  Version table:
 *** 8.21-1ubuntu5 0
        500 http://us.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
        100 /var/lib/dpkg/status

Thanks

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: coreutils 8.21-1ubuntu5
ProcVersionSignature: Ubuntu 3.13.0-32.57-generic 3.13.11.4
Uname: Linux 3.13.0-32-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.14.1-0ubuntu3.5
Architecture: amd64
CurrentDesktop: Unity
Date: Sat Dec 6 15:33:07 2014
InstallationDate: Installed on 2014-11-06 (30 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
SourcePackage: coreutils
UpgradeStatus: No upgrade log present (probably fresh install)