Libguestfs - Jun 2013 - Re: libguestfs support snapshot based virutal disk analysis?

Hi dear all:
  I have browsed almost all architecture of libGuestFs and use it on Fedora 18.
It really seems greate!
  However, 
  1. No virtual disk (*.vdi, *.vmdk...) based snashot analysis code
   Current LibGuestFs could recognize and virtual disk format (e.g. *.VDI) and
the file syste inside it (e.g. NTFS ), but find no support for snapshot virtual
disk.
   Virtual Machine such VirtualBox will generate snapshot (*.VDI for virtual
disk diff, *.sav for virtual memory diff), and these snapshots are always diff
towards based virtutual disk.
  2. So I missed this feature? Or these feature not supported now?
   If not support, so does libguestFs will support it in the future? 
   What is the effort or difficulty for this part development? Or you have any
other opitions?
  Thnaks very much for your kind reply.
Best regards

On Sun, Jun 09, 2013 at 03:40:42PM +0800, 雨居轩 wrote:
> Hi dear all:
>   I have browsed almost all architecture of libGuestFs and use it on Fedora
18. It really seems greate!
>   However, 
>   1. No virtual disk (*.vdi, *.vmdk...) based snashot analysis code
> Current LibGuestFs could recognize and virtual disk format
> (e.g. *.VDI) and the file syste inside it (e.g. NTFS ), but find
> no support for snapshot virtual disk.
libguestfs relies on qemu for all disk / format support.  So we
support whatever qemu supports.  As qemu doesn't appear to be able to
read snapshots (except for the "top" one obviously) from a VMDK or VDI
file, we can't read them either.  If support for this was added to
qemu, then libguestfs would get it for free, or nearly for free.
> Virtual Machine such VirtualBox will generate snapshot (*.VDI for
> virtual disk diff, *.sav for virtual memory diff), and these
> snapshots are always diff towards based virtutual disk.
>
>   2. So I missed this feature? Or these feature not supported now?
>    If not support, so does libguestFs will support it in the future? 
It totally depends on qemu.  You or someone would have to add this
feature to qemu.  libguestfs would get it for free after that.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org

I've used QEMU to read .vmdk snapshots.  The VM directory layout in my case
(Fusion, and I've seen Workstation do the same) created a .vmdk file per
snapshot, and qemu-img could use that .vmdk file and the base .vmdk to
convert the disk image to a raw image. IIRC there is a manifest file that
ties .vmdk files to the snapshot they represent.

So, from my experience, qemu does read disk snapshots in the .vmdk
format. It might need a little extending to also look for and parse that
manifest file, to treat a directory with .vmdk's as a snapshot tree.

Does this help?

--Alex


On Sunday, June 9, 2013, Richard W.M. Jones wrote:
> On Sun, Jun 09, 2013 at 03:40:42PM +0800, 雨居轩 wrote:
> > Hi dear all:
> >   I have browsed almost all architecture of libGuestFs and use it on
> Fedora 18. It really seems greate!
> >   However,
> >   1. No virtual disk (*.vdi, *.vmdk...) based snashot analysis code
> > Current LibGuestFs could recognize and virtual disk format
> > (e.g. *.VDI) and the file syste inside it (e.g. NTFS ), but find
> > no support for snapshot virtual disk.
>
> libguestfs relies on qemu for all disk / format support.  So we
> support whatever qemu supports.  As qemu doesn't appear to be able to
> read snapshots (except for the "top" one obviously) from a VMDK
or VDI
> file, we can't read them either.  If support for this was added to
> qemu, then libguestfs would get it for free, or nearly for free.
>
> > Virtual Machine such VirtualBox will generate snapshot (*.VDI for
> > virtual disk diff, *.sav for virtual memory diff), and these
> > snapshots are always diff towards based virtutual disk.
> >
> >   2. So I missed this feature? Or these feature not supported now?
> >    If not support, so does libguestFs will support it in the future?
>
> It totally depends on qemu.  You or someone would have to add this
> feature to qemu.  libguestfs would get it for free after that.
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> libguestfs lets you edit virtual machines.  Supports shell scripting,
> bindings from many languages.  http://libguestfs.org
>
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