Libguestfs - Oct 2017 - relaunching libguestfs with the same overlay

On Mon, Oct 02, 2017 at 11:50:42AM +0300, Maxim Kozover
wrote:
> Hi Richard!
> Could you tell me, please, if there is a way to relaunch libguestfs with
> the same overlay from the last run? The documentation tells the overlay is
> removed when the handle to libguestfs is closed.
Right, the overlay is created by libguestfs itself and thrown away
when the handle is closed:

  https://github.com/libguestfs/libguestfs/blob/master/lib/drives.c#L68
  https://github.com/libguestfs/libguestfs/blob/master/lib/launch-direct.c#L78

However you can simply create your own overlay and use that.  Run
something like:

  qemu-img create -b orig_disk -f qcow2 my_overlay

and change the guestfs_add_drive_opts call to use ?my_overlay? and
don't use the readonly flag.
> I'm talking about read-only mode so the real disks are not touched.
The above won't touch the original disk, as long as you do _not_ run
any commands such as ?qemu-img commit?.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v

Many thanks for your prompt and extensive reply, Richard!

Thanks much,

Maxim.

On Oct 2, 2017 12:22 PM, "Richard W.M. Jones" <rjones at
redhat.com> wrote:
> On Mon, Oct 02, 2017 at 11:50:42AM +0300, Maxim Kozover wrote:
> > Hi Richard!
> > Could you tell me, please, if there is a way to relaunch libguestfs
with
> > the same overlay from the last run? The documentation tells the
overlay
> is
> > removed when the handle to libguestfs is closed.
>
> Right, the overlay is created by libguestfs itself and thrown away
> when the handle is closed:
>
>   https://github.com/libguestfs/libguestfs/blob/master/lib/drives.c#L68
>   https://github.com/libguestfs/libguestfs/blob/master/lib/
> launch-direct.c#L78
>
> However you can simply create your own overlay and use that.  Run
> something like:
>
>   qemu-img create -b orig_disk -f qcow2 my_overlay
>
> and change the guestfs_add_drive_opts call to use ?my_overlay? and
> don't use the readonly flag.
>
> > I'm talking about read-only mode so the real disks are not
touched.
>
> The above won't touch the original disk, as long as you do _not_ run
> any commands such as ?qemu-img commit?.
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~
> rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-p2v converts physical machines to virtual machines.  Boot with a
> live CD or over the network (PXE) and turn machines into KVM guests.
> http://libguestfs.org/virt-v2v
>
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