[Libguestfs] [PATCH virt-v2v] v2v: Allow temporary directory to be set on a global basis.

[Richard W.M. Jones]

On Tue, Apr 07, 2020 at 01:25:39PM +0100, Daniel P. Berrangé wrote:
> On Tue, Apr 07, 2020 at 01:18:47PM +0100, Richard W.M. Jones wrote:
> > Another issue, incidental to this but related, is that we cannot use
> > the fixed appliance because docker/podman have broken support for
> > sparse files.  (It's possible to configure libguestfs to use qcow2 for
> > fixed appliances, but we don't do this now, we never really tested it,
> > and it both greatly slows down and adds more dependencies to the
> > supermin build step.)
> 
> I feel like we ought to be able to solve the slow down issue with
> qcow2, because libguestfs has a pretty narrow usage scenario.

I realize I was wrong here actually.

I meant the slow down in creating it not using it :-)

Currently supermin creates the image by truncating a raw file to the
required size and opening it directly with libext2fs.  If we use qcow2
we'd need the extra qemu-img convert step.

https://github.com/libguestfs/supermin/blob/master/src/ext2fs-c.c

Normally this is a critical path because it's the bit you wait for
when you're waiting for libguestfs to start up the first time.

However as we're talking about the fixed appliance, of course this is
done when the container is built, so it wouldn't affect the critical
path.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-df lists disk usage of guests without needing to install any
software inside the virtual machine.  Supports Linux and Windows.
http://people.redhat.com/~rjones/virt-df/