Kernel msg structure

The kernel stores each message in the queue within the framework of the msg structure. It is defined for us in linux/msg.h as follows:

/* one msg structure for each message */
struct msg {
    struct msg *msg_next;   /* next message on queue */
    long  msg_type;
    char *msg_spot;         /* message text address */
    short msg_ts;           /* message text size */
};

msg_next

This is a pointer to the next message in the queue. They are stored as a singly linked list within kernel addressing space.

msg_type

This is the message type, as assigned in the user structure msgbuf.

msg_spot

A pointer to the beginning of the message body.

msg_ts

The length of the message text, or body.