[Libguestfs] [PATCH v2v 0/5] convert: Find out if Windows guest is expecting BIOS localtime or UTC

[Alice: See patch 2] [This patch is a bit rough, it could do with better commit messages and some tests. Please test it to see if it solves the Windows conversion issue described in the thread below.] We currently do not set any <clock/> field in guest output. Most Windows guests expect the BIOS to be set to localtime, whereas almost all Linux guests would expect it to be set to UTC. It is also possible to configure a Windows guest to expect BIOS set to UTC. The default is usually BIOS set to UTC, so for many Windows guests this would be wrong. This specifically may cause problems when scheduling qemu-ga installation, see the thread here: https://listman.redhat.com/archives/libguestfs/2023-September/thread.html... but could cause other general issues with time in the guest. One way to implement this would be to copy the source hypervisor information across; however I'm not confident this information is read correctly. A better way is to read out what the guest is expecting from the Windows registry. (For Linux we just assume BIOS is always UTC, since that's the default for almost any Linux guest which hasn't been dual-booted with Windows, which for VMs would be incredibly rare.) Rich.