otw !!!
Glen "Big Baby" Davis posted a farewell message to his fans on Tuesday just before he was thrown behind prison bars ... and the former NBA star was surprisingly in good spirits despite what's in store for him.
Check out footage that Davis posted to his Instagram page while he said he was on his way to FPC Duluth in Minnesota ... he had a big smile on his face -- even though he's now about serve the 40-month prison sentence he was hit with earlier this year for his role in a scheme that defrauded the NBA's Players' Health and Benefit Welfare Plan.