df(windows): fix Avail/Use% by using number_of_free_clusters for bavail

[naoNao89]

Fix Windows df incorrectly reporting 0 bytes available and 100% usage for all filesystems. The issue was caused by hardcoding bavail (blocks available to non-privileged processes) to 0 instead of using the actual free clusters from Windows API.

On Windows, all mounted filesystems displayed:

• Avail: 0 bytes (always)
• Use%: 100% (always)
• --total flag: Completely broken aggregation

This made df output useless for Windows users.

Before (Broken)

Filesystem               Size  Used Avail Use%
\Device\HarddiskVolume2  256G  180G     0 100%
\Device\HarddiskVolume3  677G  494G     0 100%
\Device\HarddiskVolume4  1.9T  1.8T     0 100%
\Device\HarddiskVolume1   50M   35M     0 100%
\Device\HarddiskVolume8   11T  5.9T     0 100%

After (Fixed)

Filesystem               Size  Used Avail Use%
\Device\HarddiskVolume2  256G  180G  76G  70%
\Device\HarddiskVolume3  677G  494G 183G  73%
\Device\HarddiskVolume4  1.9T  1.8T 100G  95%
\Device\HarddiskVolume1   50M   35M  15M  70%
\Device\HarddiskVolume8   11T  5.9T 5.1T  54%

Windows API Context

The fix correctly implements POSIX semantics on Windows:

POSIX	Windows	Meaning
f_bfree	lpNumberOfFreeClusters (no quota consideration)	Total free clusters
f_bavail	lpNumberOfFreeClusters (quota-aware)	Free clusters available to user

Windows GetDiskFreeSpaceW() already respects disk quotas, making this fix semantically correct.

Fixes

Closes #7461

Related Issues

• test_file_column_width_if_filename_contains_unicode_chars started to fail recently #5015: df tests failing on Windows (tests were disabled) - can now be re-enabled
• df: Fix overflow error on WSL. Default to 0 when the values are non-sense. #5381: df overflow error on WSL (fixed) - works better with correct bavail

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

[sylvestre]

could you please add a test to make sure we don't regress in the future? thanks

[naoNao89]

done assert!(fs_usage.bavail >= 0);

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)

[sylvestre]

@naoNao89 i was thinking about tests/by-util/test_df.rs

[codspeed-hq]

CodSpeed Performance Report

Merging #9470 will not alter performance

_{Comparing naoNao89:fix/df-windows-bavail (586f6b7) with main (b9f97d4)}

Summary

✅ 126 untouched
⏩ 6 skipped¹

Footnotes

1. 6 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)