Function measure_verity_opt 

pub fn measure_verity_opt<H: FsVerityHashValue>(
    fd: impl AsFd,
) -> Result<Option<H>, MeasureVerityError>

Measures fs-verity on the given file.

This essentially boils down to the FS_IOC_MEASURE_VERITY ioctl.

This is the _opt() variant of measure_verity(). If the file doesn’t have fs-verity enabled, or resides on a filesystem where fs-verity is unsupported, this function returns None. Other errors are still passed through.