How to specific volume in window in os file?

[hotrungnhan]

I using backend package to use local file.
Issue is vfs keep the temp file in C drive, because i put my source code in D drive ,so vfs will make a file in D drive. but when i close the file vfs can't rename it back output file due to difference drive.

[funkyshu]

Thanks for your bug report. One area of real neglect with vfs is interacting with Windows. I'm fairly certain our tests would fail miserably on Windows. I'll try to take a look this weekend.

[funkyshu]

Thanks for reporting this! You’re right—on Windows, os.Rename() fails when trying to move files across different volumes (e.g., from C:\ to D:). This is a platform-level limitation that’s causing issues when VFS creates temp files using the system temp directory but the target file is on another drive.

We’ve avoided creating temp files in the same directory as the destination because many VFS users are watching those directories with polling or file events, and intermediate files can trigger noisy or misleading events.

✅ Proposed Strategy

We’re planning to update the os backend to use the following fallback order when writing temp files:
1. Use Options.TempDir if explicitly provided
2. Use os.TempDir() if it lives on the same volume or filesystem as the destination
3. Use a .vfs-temp/ directory at the root of the destination volume
4. Use a .vfs-temp/ subdirectory of the destination file’s parent
5. As a final fallback: create the temp file in the same directory as the destination

All approaches ensure that:
• The rename is safe across volumes or filesystems
• We minimize accidental watcher triggers
• Cleanup is predictable

We’ll also add platform-aware logic to detect volume boundaries on Windows and filesystem boundaries on Unix (via syscall.Statfs()).