kdmsg_msg
msg = kmalloc(offsetof(struct kdmsg_msg, any) + hbytes,
struct kdmsg_msg;
int (*func)(struct kdmsg_state *, struct kdmsg_msg *);
TAILQ_ENTRY(kdmsg_msg) qentry; /* serialized queue */
typedef struct kdmsg_msg kdmsg_msg_t;
TAILQ_HEAD(, kdmsg_msg) msgq; /* transmit queue */