Win32 app can't open file on WSL file system - potential causes?

[Joshua-Schroijen]

Hello everyone,

I am facing a weird problem. In my corporate environment we have a proprietary Win32 CLI program (which I can't disclose a lot about and is also a black box to us) that I would like to invoke like this from inside WSL2:

foo.exe '\\wsl.localhost\Ubuntu\tmp\bar.baz'

This doesn't work: foo says it can't open \\wsl.localhost\Ubuntu\tmp\bar.baz

However, if I copy bar.baz to a different network share and execute

foo.exe '\\ourtrustynetworkshare\stuff\bar.baz'

foo.exe can work with the file just fine.
I can also work with \\wsl.localhost\Ubuntu\tmp\bar.baz using different Win32 applications such as Notepad without any issues.
Finally, creating a symbolic link on the C: drive or mapping \\wsl.localhost\Ubuntu to a drive letter doesn't help.

So to recap:

• My file of interest on the WSL2 file system appears to be accessible to any Windows program using its UNC path
• My application of interest can access files on a network share using a UNC path
• • ... but my application of interest for some bizarre reason can't access my file of interest, neither through a UNC path nor over a symbolic link on the system root to a UNC path

I was wondering whether anyone has some general knowledge on why Win32 programs could face these challenges and how this could be worked around

I thought about implementing a sort of "copy on read" scheme to copy the needed file to the Windows file system before invoking foo.exe but this could incur too high a performance penalty.

Thanks so much in advance for your input!