Laszlo Ersek
2023-Sep-25 15:48 UTC
[Libguestfs] [PATCH v2v 0/5] convert: Find out if Windows guest is expecting BIOS localtime or UTC
On 9/25/23 16:04, Richard W.M. Jones wrote:> [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#32556 > > 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.)I think the word "BIOS" is incorrectly used all over the series; I'd rather say "RTC" / "real time clock". Laszlo
Laszlo Ersek
2023-Sep-25 15:49 UTC
[Libguestfs] [PATCH v2v 0/5] convert: Find out if Windows guest is expecting BIOS localtime or UTC
On 9/25/23 17:48, Laszlo Ersek wrote:> On 9/25/23 16:04, Richard W.M. Jones wrote: >> [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#32556 >> >> 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.) > > I think the word "BIOS" is incorrectly used all over the series; I'd > rather say "RTC" / "real time clock".... meaning patch subject lines, commit message bodies, and code.