I'm not necessarily saying this is a bug, but a change in behaviour in qemu has caused virt-v2v to fail. The reproducer is quite simple.
Create sparse and preallocated qcow2 files of the same size: $ qemu-img create -f qcow2 sparse.qcow2 50M Formatting 'sparse.qcow2', fmt=qcow2 size=52428800 cluster_size=65536 lazy_refcounts=off refcount_bits=16 $ qemu-img create -f qcow2 prealloc.qcow2 50M -o preallocation=falloc,compat=1.1 Formatting 'prealloc.qcow2', fmt=qcow2 size=52428800 compat=1.1 cluster_size=65536 preallocation=falloc lazy_refcounts=off refcount_bits=16 $ du -m sparse.qcow2 prealloc.qcow2 1 sparse.qcow2 51 prealloc.qcow2 Now copy the sparse file into the preallocated file using the -n option so qemu-img doesn't create the target: $ qemu-img convert -p -n -f qcow2 -O qcow2 sparse.qcow2 prealloc.qcow2 (100.00/100%) In new qemu that makes the target file sparse: $ du -m sparse.qcow2 prealloc.qcow2 1 sparse.qcow2 1 prealloc.qcow2 <-- should still be 51 In old qemu the target file remained preallocated, which is what I and virt-v2v are expecting. I bisected this to the following commit: 4d7c487eac1652dfe4498fe84f32900ad461d61b is the first bad commit commit 4d7c487eac1652dfe4498fe84f32900ad461d61b Author: Max Reitz <mre...@redhat.com> Date: Wed Jul 24 19:12:29 2019 +0200 qemu-img: Fix bdrv_has_zero_init() use in convert bdrv_has_zero_init() only has meaning for newly created images or image areas. If qemu-img convert did not create the image itself, it cannot rely on bdrv_has_zero_init()'s result to carry any meaning. Signed-off-by: Max Reitz <mre...@redhat.com> Message-id: 20190724171239.8764-2-mre...@redhat.com Reviewed-by: Maxim Levitsky <mlevi...@redhat.com> Reviewed-by: Stefano Garzarella <sgarz...@redhat.com> Signed-off-by: Max Reitz <mre...@redhat.com> qemu-img.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) Reverting this commit on the current master branch restores the expected behaviour. Thoughts? 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, bindings from many languages. http://libguestfs.org