Use this for VHD and VMDK to avoid allocating space in the image
for empty sectors.
Note that this negatively affects performance because mkimg uses a
temporary file for the intermediate storage. When mkimg has better
internal book keeping, performance can be significantly improved.
among others.
Add an undocumented option for unit testing (-y). When given, the image
will have UUIDs and timestamps synthesized in a way that gives identical
results across runs. As such, UUIDs stop being unique, globally or
otherwise.
VHD support requested by: gjb@
Add support for different output formats:
1. The output file that was previously written is now called the raw format.
2. Add the vmdk output format to create VMDK images.
When the format is not given, the raw output format is assumed.
