MSGCTL(2-SVR4)      RISC/os Reference Manual       MSGCTL(2-SVR4)



NAME
     msgctl - message control operations

SYNOPSIS
     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/msg.h>

     int msgctl(int msqid, int cmd, .../* struct msqid_ds *buf */);

DESCRIPTION
     msgctl provides a variety of message control operations as
     specified by cmd.  The following cmds are available:

     IPC_STAT    Place the current value of each member of the
                 data structure associated with msqid into the
                 structure pointed to by buf.  The contents of
                 this structure are defined in intro(2).

     IPC_SET     Set the value of the following members of the
                 data structure associated with msqid to the
                 corresponding value found in the structure
                 pointed to by buf:
                       msg_perm.uid
                       msg_perm.gid
                       msg_perm.mode  /* only access permission bits */
                       msg_qbytes

                 This cmd can only be executed by a process that
                 has an effective user ID equal to either that of
                 superuser, or to the value of msg_perm.cuid or
                 msg_perm.uid in the data structure associated
                 with msqid.  Only superuser can raise the value
                 of msg_qbytes.

     IPC_RMID    Remove the message queue identifier specified by
                 msqid from the system and destroy the message
                 queue and data structure associated with it.
                 This cmd can only be executed by a process that
                 has an effective user ID equal to either that of
                 superuser, or to the value of msg_perm.cuid or
                 msg_perm.uid in the data structure associated
                 with msqid.

     msgctl fails if one or more of the following are true:

     EACCES         cmd is IPC_STAT and operation permission is
                    denied to the calling process [see intro(2)].

     EFAULT         buf points to an illegal address.

     EINVAL         msqid is not a valid message queue



                        Printed 11/19/92                   Page 1

MSGCTL(2-SVR4)      RISC/os Reference Manual       MSGCTL(2-SVR4)



                    identifier.

     EINVAL         cmd is not a valid command.

     EINVAL         cmd is IPC_SET and msg_perm.uid or
                    msg_perm.gid is not valid.

     EOVERFLOW      cmd is IPC_STAT and uid or gid is too large
                    to be stored in the structure pointed to by
                    buf.

     EPERM          cmd is IPC_RMID or IPC_SET. The effective
                    user ID of the calling process is not that of
                    super user, or the value of msg_perm.cuid or
                    msg_perm.uid in the data structure associated
                    with msqid.

     EPERM          cmd is IPC_SET, an attempt is being made to
                    increase to the value of msg_qbytes, and the
                    effective user ID of the calling process is
                    not that of superuser.

SEE ALSO
     intro(2), msgget(2), msgop(2).

DIAGNOSTICS
     Upon successful completion, a value of 0 is returned. Other-
     wise, a value of -1 is returned and errno is set to indicate
     the error.


























 Page 2                 Printed 11/19/92