virtofs: errors when accessing with c++ std::filesystem

[MichaelDietzel]

Describe the bug
I am trying to launch the game factorio (1.1.87) from my virtiofs. However I get an error message that apparently originates from c++ std::filesystem. Translated to english it is something like: "weakly_canonical: There is no file system detected on the disk. Make sure all required file system drivers are loaded and the disk is not damaged." Launching from a real ntfs works flawlessly.

I tried the following, but it did not help:

• I tried the factorio-version from steam as well as the paid version and the free demo directly downloaded from factorio.com (afaik without drm).
• I first tried the drivers from virtio-win-0.1.229.iso from fedora, then I copiled them myself from master.
• I set the registry key for virtiofs to be case insensitive (does not seem to work well with the drivers from virtio-win-0.1.229.iso, works kind of ok with master)
• I set the registry key for virtiofs to report itself as nfts (does not work at all with the drivers from virtio-win-0.1.229.iso, but it works with master).

My bug report in the factorio forums where they tell they just use c++ std::filesystem.

To Reproduce
Steps to reproduce the behaviour:

1. set up a windows 10 vm that can run factorio from a regular ntfs. It probably needs graphics acceleration, I passed through a Nvidia GTX 1060. Maybe you do not even need the graphics acceleration as the error may trigger before needing any. I have not tested it without, though.
2. install virtiofs using winfsp 2.0
3. set up virtiofs on Z:, configured to be case insensitive + report to be ntfs
4. download the zip-version of the free demo of factorio from factorio.com and unpack it on Z:
5. launch factorio (\bin\x64\factorio.exe)

Expected behavior
Factorio launches without any error message. As do a few other steam-games I tested.

Screenshots

Host:

• Disto: Ubuntu 22.04
• Kernel version: 5.15.0-67 with a patch for creative x-fi soundcard passthrough
• QEMU version: 6.2.0
• libvirt version: 8.0.0
• The storage for virtiofs is on zfs

VM:

• Windows 10 21H2
• virtiofs
• Driver version or commit hash that was used to build the driver: 0.1.229.iso and 65cea19

[viktor-prutyanov]

The issue is the same as #517

#include <iostream>
#include <filesystem>

int main()
{
	auto p = std::filesystem::path("Z:\\");

	try
	{
		auto p2 = std::filesystem::weakly_canonical(p);
		std::cout << p2 << std::endl;
	}
	catch (const std::exception& ex)
	{
		std::cout << ex.what() << std::endl;
	}

	return 0;
}

With -m Z:

weakly_canonical: The volume does not contain a recognized file system.                                                 Please make sure that all required file system drivers are loaded and that the volume is not corrupted.: "Z:\" 

With -m \\.\Z (global mount):

Z:\\

[viktor-prutyanov]

@MichaelDietzel
There is a workaround for your use: use global mount (i.e. mount \\.\Z: instead of Z:\)