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ERROR_FLT_INSTANCE_NOT_FOUND
An instance is more specific than a filter
ERROR_FLT_INSTANCE_NOT_FOUND means that Filter Manager could not locate an attached instance matching the requested filter, volume, and optional instance name. A registered filter can exist without an instance on a particular volume, and a filter can have multiple instances. This is why a successful filter lookup does not prove that a later instance lookup or detach operation will succeed.
FltGetVolumeInstanceFromName searches the attached instances on the specified volume from higher to lower altitude. If no instance name is supplied, it returns the highest matching instance. That selection rule is important when an administrative tool assumes that a default instance is the only one.
What to check
- Verify all three lookup dimensions: registered filter, current volume object, and instance name. A valid value for any two does not identify the third.
- Use
fltmc instancesto inspect actual attachments before asking a driver to detach or query a named instance. - Account for time-of-check changes. The instance may have been intentionally declined during setup, detached, or begun teardown between discovery and use.
- Do not replace this status with a retry loop that assumes attachment must happen. Check the instance setup policy and the volume eligibility rules first.
References
- Microsoft: FltGetVolumeInstanceFromName
- Microsoft: FltDetachVolume
- OSR: the Filter Manager instance model
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