OVMF/QEMU shell based unit tests and writing to a virtual disk

["Sean" <spbrogan@outlook.com>]

Laszlo and others familiar with QEMU,

I am trying to write automation that boots QEMU/OVMF and then runs EFI 
applications and those efi applications then use the UEFI shell apis to 
write back to the disk their state.  I am seeing very inconsistent 
results with sometimes it working fine while other times the disk 
contents are invalid.  If i run multiple tests it seems like the first 
two work while the 3rd seems to start failing but overall it seems random.

Failing means:
	Disk contents corrupted but present.
	Disk contents wrong size (short).
	Files that show written in UEFI shell never show up on host.

I am trying to determine if this is a known limitation with QEMU or a 
bug i need to track down in the unit test code.

My setup:

This is on a Windows 10 x64 host.  I am running current 5.1 version of 
QEMU.

My script creates a folder in the Windows NTFS file system.  Copies the 
EFI executables and startup.nsh files to it.  Then starts QEMU with the 
following additional parameter.

  -drive file=fat:rw:{VirtualDrive},format=raw,media=disk

VirtualDrive is the Windows file path of the said mentioned folder.


If interested you should be able to reproduce the results by pulling my 
branch and/or you can review the above.

You can see the operations here:

PR: https://github.com/microsoft/mu_tiano_platforms/pull/1

My Branch: 
https://github.com/spbrogan/mu_tiano_platforms/tree/personal/sebrogan/shellunittests

Or if interested you can reproduce it by following steps defined here:

https://github.com/spbrogan/mu_tiano_platforms/blob/personal/sebrogan/shellunittests/Platforms/QemuQ35Pkg/Docs/building.md

and more details here
https://github.com/spbrogan/mu_tiano_platforms/blob/personal/sebrogan/shellunittests/Platforms/QemuQ35Pkg/Plugins/QemuRunner/ReadMe.md

After building qemu with the right parameters for your environment you 
can run <your stuart_build cmd> --flashonly MARK_STARTUP_NSH=TRUE 
RUN_UNIT_TESTS=TRUE

For example in my environment it looks like
stuart_build -c Platforms\QemuQ35Pkg\PlatformBuild.py 
TOOL_CHAIN_TAG=VS2019 --flashonly RUN_UNIT_TESTS=TRUE MAKE_STARTUP_NSH=TRUE


Anyway if i recall correctly last year when we talked briefly about 
automation there was some concern that this would happen. Any 
information and/or ideas would be greatly appreciated.

Thanks
Sean