msg(FP)                        6 January 1993                        msg(FP)


 Name

    msg - IPC message structures

 Syntax


    #include <sys/msg.h>


 Description

    A message queue identifier (msqid) is a unique positive integer created
    by a msgget(S) system call.  Each msqid has a message queue and a data
    structure associated with it.  The data structure is referred to as
    msqidds and contains the following members:

       struct  ipc_perm msg_perm;       /* operation permission struct */
       struct  msg *msg_first;          /* ptr to first message on q */
       struct  msg *msg_last;           /* ptr to last message on q */
       ushort  msg_cbytes;              /* current number of bytes on q */
       ushort  msg_qnum;                /* number of msgs on q */
       ushort  msg_qbytes;              /* max number of bytes on q */
       ushort  msg_lspid;               /* pid of last msgsnd operation */
       ushort  msg_lrpid;               /* pid of last msgrcv operation */
       time_t  msg_stime;               /* last msgsnd time */
       time_t  msg_rtime;               /* last msgrcv time */
       time_t  msg_ctime;               /* last change time */
                                        /* Times measured in secs since */
                                        /* 00:00:00 GMT, Jan. 1, 1970 */


    msgperm is an ipcperm structure that specifies the message operation
    permission.  The structure includes the following members:

       ushort  uid;        /* owner's user id */
       ushort  gid;        /* owner's group id */
       ushort  cuid;       /* creator's user id */
       ushort  cgid;       /* creator's group id */
       ushort  mode;       /* r/w permission */
       ushort  seq;        /* slot usage sequence number */
       key_t   key;        /* key */


    msgqnum is the number of messages currently on the queue. msgqbytes is
    the maximum number of bytes allowed on the queue. msglspid is the pro-
    cess ID of the last process that performed a msgsnd operation. msglrpid
    is the process ID of the last process that performed a msgrcv operation.
    msgstime is the time of the last msgsnd operation, msgrtime is the time
    of the last msgrcv operation, and msgctime is the time of the last
    msgctl(S) operation that changed a member in the preceding structure.

 See also

    msgctl(S), msgget(S), msgop(S)