S3CSI-225: Port prefix parsing fix from upstream PR #658

[anurag4DSB]

Summary

• Fix S3 bucket prefix parsing that could silently mount the wrong prefix or fail
• Root cause: old parser always tried = split first, corrupting prefixes with = characters
• New parser finds both separator positions, uses whichever appears first

Changes

• pkg/mountpoint/args.go: Replace ParseArgs() parsing logic with upstream fix
• pkg/mountpoint/args_test.go: Add 4 new regression test cases for prefixes with =

Test Plan

• 14/14 TestParsingMountpointArgs unit tests pass (including 4 new)
• Regression case: "prefix kwk3-di/sub=vault/" correctly parses to --prefix=kwk3-di/sub=vault/
• E2E test: New test verifies prefix values containing = signs (e.g., prefix=env=prod/) work correctly end-to-end — files stored under the full prefix in S3
• CI E2E: Mount options suite has 3 existing prefix tests: isolation, prefix usage, and bidirectional S3 API visibility.

Issue: S3CSI-225

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.92%. Comparing base (75ee0ef) to head (f46bc9b).
✅ All tests successful. No failed tests found.

Additional details and impacted files

Files with missing lines	Coverage Δ
pkg/mountpoint/args.go	100.00% <100.00%> (ø)

@@            Coverage Diff             @@
##             main     #324      +/-   ##
==========================================
+ Coverage   71.89%   71.92%   +0.02%     
==========================================
  Files          47       47              
  Lines        2669     2671       +2     
==========================================
+ Hits         1919     1921       +2     
  Misses        622      622              
  Partials      128      128