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ERROR_FLT_DO_NOT_ATTACH
An explicit per-volume policy decision
ERROR_FLT_DO_NOT_ATTACH is commonly a deliberate return value from a minifilter's InstanceSetupCallback. Filter Manager calls that callback when it considers automatic or manual attachment. Returning this status prevents creation of the instance on the selected volume; it does not say that the minifilter binary failed to load.
The callback receives the volume device type, filesystem type, and flags describing why attachment is being attempted. A filter can use those inputs to exclude unsupported filesystems, removable media, network filesystems, developer volumes, or any scope that its own policy intentionally leaves unfiltered.
What to check
- Log the decision together with the instance-setup flags and filesystem type, so an intentional policy exclusion is distinguishable from an accidental broad rejection.
- Keep the callback short. Microsoft specifically warns against thread synchronization and interprocess communication there because they can create deadlocks during attachment.
- Check the INF instance configuration and the filter's own eligibility rules before forcing a manual attach. A manual request still reaches the instance setup policy.
- Retry only when the reason for declining has changed, such as a newly mounted eligible volume or a corrected configuration. Repeated attachment attempts do not change the callback result by themselves.
References
- Microsoft: PFLT_INSTANCE_SETUP_CALLBACK
- Microsoft: minifilter load order groups and altitudes
- OSR: instances and Filter Manager attachment model
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