fix: improve logging while unmount external mount

[raj-prince]

Description

• Adding info unmount logs when unmount failed for externally managed mount point.
• Corresponding jacobsa/fuse change - Returning custom error while unmounting /dev/fd/N kind of mount point jacobsa/fuse#179

Tested in GKE Environment:

I0717 16:45:04.019697       1 main.go:124] received SIGTERM signal, waiting for all the gcsfuse processes exit...
I0717 16:45:04.019728       1 main.go:127] the sidecar mounter is calling ctx.cancel
I0717 16:45:04.019768       1 sidecar_mounter.go:112] context marked as done, sleep for 5 seconds, to evaluate gcsfuse process 22 exit state
I0717 16:45:04.019778       1 sidecar_mounter.go:102] sending SIGTERM to gcsfuse process: /gcsfuse --app-name gke-gcs-fuse-csi --foreground --gid 0 --config-file /gcsfuse-tmp/.volumes/gcs-fuse-warp-test-volume/config.yaml --enable-cloud-profiling --log-severity trace --uid 0 --temp-dir /gcsfuse-buffer/.volumes/gcs-fuse-warp-test-volume/temp-dir --prometheus-port 62990 --implicit-dirs gcs-fuse-warp-test-bucket /dev/fd/3
{"timestamp":{"seconds":1752770704,"nanos":20034872},"severity":"INFO","message":"Received SIGTERM, attempting to unmount..."}
{"timestamp":{"seconds":1752770704,"nanos":20203944},"severity":"INFO","message":"Mount point /dev/fd/3 is externally managed; gcsfuse will not unmount it."}
W0717 16:45:09.021438       1 sidecar_mounter.go:115] after 5 seconds, process with id 22 has not exited, force kill the process
E0717 16:45:09.023106       1 logger.go:60] gcsfuse exited with error: signal: killed
I0717 16:45:09.023207       1 main.go:133] exiting sidecar mounter...

Link to the issue in case of a bug fix.

b/431732751

Testing details

1. Manual - Tested in GKE environment.
2. Unit tests - NA
3. Integration tests - NA

Any backward incompatible change? If so, please explain.

[gemini-code-assist]

Summary of Changes

Hello @raj-prince, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on refining the logging behavior during the unmount process, particularly for scenarios involving externally managed mount points. The change aims to reduce noise in error logs by classifying expected unmount failures as informational messages, thereby improving the clarity and actionability of system logs. It also includes a necessary dependency update to facilitate this logging improvement.

Highlights

• Improved Logging for Unmount Failures: I've updated the unmount logic to provide more granular logging. Specifically, if an unmount operation fails because the mount point is externally managed (i.e., not controlled by gcsfuse), it will now be logged as an INFO message rather than an ERROR. This helps distinguish expected unmount scenarios from actual issues.
• Dependency Update: To support the new fuse.ErrExternallyManagedMountPoint error type used in the improved logging, I've updated the github.com/jacobsa/fuse dependency to a newer version.

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[gemini-code-assist]

Code Review

This pull request improves the logging for a specific unmount error, which is a good enhancement to reduce log noise. The dependency updates in go.mod and go.sum are appropriate for this change.

My main feedback is on the signal handler's control flow in cmd/legacy_main.go. The current implementation, both before and after this change, can cause the process to hang if an unmount operation fails. I've added a suggestion to address this for the new case being handled, which will improve the shutdown behavior.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 79.56%. Comparing base (93ca472) to head (0a68cf1).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
cmd/legacy_main.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3540      +/-   ##
==========================================
- Coverage   79.56%   79.56%   -0.01%     
==========================================
  Files         141      141              
  Lines       18920    18929       +9     
==========================================
+ Hits        15053    15060       +7     
- Misses       3359     3362       +3     
+ Partials      508      507       -1     

Flag	Coverage Δ
unittests	79.56% <0.00%> (-0.01%)	⬇️

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[raj-prince]