Most barbecue sauces have either a ketchup or mustard base; this one has both.
Soak wood in water 1 hour.
Cook mustard and next 6 ingredients in a large saucepan over low heat, stirring often, 20 minutes; remove from heat, and set aside.
Cut several deep slits in roast using a paring knife. Stir together garlic, salt, and pepper; rub on all sides of roast.
Prepare charcoal fire in smoker; let burn 15 to 20 minutes.
Drain wood; place on coals. Place water pan in smoker; add water to fill line.
Place pork roast in center of lower food rack. Pour 1 cup mustard mixture over roast.
Cook, covered with smoker lid, 6 to 7 hours or until a meat thermometer inserted into thickest portion registers 165°, adding additional wood and charcoal every hour as needed. Remove roast from smoker; cool slightly. Chop and serve with remaining mustard sauce.