vuid_q_node
struct vuid_q_node *top; /* input queue head (first in line) */
struct vuid_q_node *bottom; /* input queue head (last in line) */
struct vuid_q_node *free; /* input queue free list */
struct vuid_q_node *next; /* Next item in queue */
struct vuid_q_node *prev; /* Previous item in queue */