wslbridge hangs when running elevated and non-elevated WSL instances simultaneously

[rprichard]

See mintty/wsltty#43 (comment).

wslbridge won't work in this situation, but it should try to fail gracefully.

[rprichard]

Survey of Windows versions:
10586: no WSL feature
14393: simultaneous elevated and non-elevated instances allowed, redirecting stdout is not (Error: 0x80070057)
15063: simultaneous elevated and non-elevated instances not allowed, redirecting stdout is

I guess wslbridge can detect 15063 and up (how?), then redirect stdout to a pipe and detect the error.

[mintty]

  FILE * pf = popen("cmd /C ver", "r");
  fgets(line, sizeof line, pf)); fgets(line, sizeof line, pf));

[rprichard]

 FILE * pf = popen("cmd /C ver", "r");
 fgets(line, sizeof line, pf)); fgets(line, sizeof line, pf));

Maybe. I wonder about: (a) performance, (b) security/reliability, and (c) localization. I think I'd prefer if it queried the System32 directory and invoked cmd.exe without doing a PATH lookup. I'm guessing localization isn't an issue, because the string is "\nMicrosoft Windows [Version 10.0.15063]\n". Maybe the Version part is translated, but I suppose it'd be possible to look for a trailing version-and-right-bracket at the end of the second line. I benchmarked it in my Win10 VM, and it usually took ~11ms on repeated runs, but it sometimes took up to ~30ms.

I tried GetVersionEx, and it worked fine (e.g. returned the 15063 dwBuildNumber) with fully-updated MSYS2 and Cygwin compilers. I guess they automatically provide the necessary manifest, so I'm currently preferring this approach.

[rprichard]

If the EXE had no manifest at all, then GetVersionEx would return Windows 8. Windows 8 doesn't have WSL, so the program could abort.

[mintty]

Wow! What a tremendous effort to capture an error message. Thanks a lot for committing this.

[mintty]

@rprichard, can you make this a release, please? So I can again refer to a well-defined version from wsltty?

[rprichard]

Ok, the fix for this issue is now released in version 0.2.2.