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fix: false success in unmount flow #182

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Merged
stapelberg merged 2 commits into from
Aug 29, 2025
Merged

fix: false success in unmount flow #182

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891da64
fix: false success in unmount flow
raj-prince Aug 27, 2025
365a485
review comments.
raj-prince Aug 28, 2025
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1 change: 1 addition & 0 deletions unmount_linux.go
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ func unmount(dir string) error {
if strings.HasPrefix(dir, "/dev/fd/") {
return fmt.Errorf("%w: %s", ErrExternallyManagedMountPoint, err)
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@gargnitingoogle gargnitingoogle Aug 27, 2025

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Is it not possible or not desirable to wrap both errors here ? e.g. something like

Suggested change
return fmt.Errorf("%w: %s", ErrExternallyManagedMountPoint, err)
return fmt.Errorf("%w: %w", ErrExternallyManagedMountPoint, err)

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@raj-prince raj-prince Aug 28, 2025

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I think, not desirable. Also, Unwrap doesn't work in multi %w scenario - https://go.dev/play/p/3aixFmasPAK

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@gargnitingoogle gargnitingoogle Aug 29, 2025 •
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In the sample you attached (thanks for it BTW), I see that the errors.Is returns true for both errors on the combined error, but errors.Wrap return nil on it, which is surprizing a bit.

Error: externally managed mount point: EOF
  errors.Is(errWW, ErrExternallyManagedMountPoint): true
  errors.Is(errWW, ErrUnderlying): true
  errors.Unwrap(errWW): <nil>

I am just worried that not wrapping the returned error on the original error would just lose information. There is a way to wrap multiple errors, that can be also be returned using UnWrap e.g. in this sample https://go.dev/play/p/VarDGW6zVe6 , but it's definitely not very easy to use. It returns this:

  errors.Is(errWW, ErrExternallyManagedMountPoint): true
  errors.Is(errWW, ErrUnderlying): true
Unwrapped error 1: externally managed mount point
Unwrapped error 2: EOF

}
return err
}
return nil
}
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7 changes: 5 additions & 2 deletions unmount_linux_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,10 @@ func Test_umountNoCustomError(t *testing.T) {
t.Setenv("PATH", "") // Clear PATH to fail unmount with fusermount is not found

err := unmount("/dev")
if err != nil && errors.Is(err, ErrExternallyManagedMountPoint) {
t.Errorf("Not expected custom error.")
if err == nil {
t.Fatal("Expected error but got none.")
}
if errors.Is(err, ErrExternallyManagedMountPoint) {
t.Error("Custom error was not expected.")
}
}
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