Re: [Qemu-devel] [PATCH 2/2] qemu-nbd: Add --image-size option

["Richard W.M. Jones" <rjones@redhat.com>]

On Tue, Sep 20, 2016 at 01:35:29PM +0200, Tomáš Golembiovský wrote:
> The second patch tries to solve the situation when you have file:
> 
>     || some data ; image ; some more data ||
> 
> In this case there is no way to say where the image ends and client may
> also access content in the "some more data" area. Thus corrupting the
> data outside the image.

Some background:

A use case for this is to be able to access a disk image which is
located inside an OVA file, without unpacking the OVA.  An OVA file is
[usually, not always] an uncompressed tar file.  It is relatively easy
to find the offset and size of the contained disk image, since tar
files are essentially concatenations of header + data + header + ...

OVA files may be terabytes in size, so avoiding unpacking is desirable
since it can save masses of disk space and time.

One place we could use this feature would be in virt-v2v.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html