[Libguestfs] libguestfs-tools and NTFS compression attribute

[Richard W.M. Jones]

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On Mon, Jun 13, 2016 at 04:03:20PM +0200, Vlastimil Burián wrote:
> Hello Richard,
> 
> I need a little help with libguestfs-tools
> 
> I used it as follows:
> 
> |sudo guestmount -a thevirtualdisk.vhdx -i /mnt/anydirectory |
> 
> 
> But so far I have no clue as to if it is possible and if yes, then how
> to clear the NTFS compression attribute(?) supposing I have mounted a
> virt. disk NTFS compressed.
> 
> https://serverfault.com/questions/783548/hyper-v-how-to-connect-compressed-ntfs-storage-or-convert-it

If you just want to do it with libguestfs and don't need to automate
the process (ie. you're only doing it one-off for a few disks), then
it's better to use virt-rescue.  Something like this:

$ virt-rescue -a thedisk
><rescue> mount /dev/sda2 /sysroot
><rescue> cd /sysroot
><rescue> setfattr -h -v 0x00000000 -n system.ntfs_attrib directory-name

(See also:
http://www.tuxera.com/community/ntfs-3g-advanced/data-compression/)

You can also use the regular getfattr command to list the attribute,
although the format seems to need a bit of decoding:

><rescue> mkdir compressed
><rescue> setfattr -h -v 0x00080000 -n system.ntfs_attrib compressed
><rescue> mkdir uncompressed
><rescue> setfattr -h -v 0x00000000 -n system.ntfs_attrib uncompressed
><rescue> getfattr -n system.ntfs_attrib compressed 
# file: compressed
system.ntfs_attrib=0sEAgAAA==
><rescue> getfattr -n system.ntfs_attrib uncompressed/
# file: uncompressed/
system.ntfs_attrib=0sEAAAAA==

Unfortunately these attributes are not passed through FUSE.  I suspect
that is because they are in the system.* namespace which the kernel
handles specially, but there are also a bunch of bugs associated with
extended attributes & guestmount and maybe this is one of them.

It should be possible to read and set the attributes through the API
(eg. using guestfish).  See the APIs guestfs_lsetxattr and
guestfs_lgetxattr and related.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
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