msgctl(PCI)                    6 January 1993                    msgctl(PCI)


 Name

    msgctl - message control operations

 Syntax


    #include <pcilib.h>


    #include <memmdl.h>


    #include <ipc.h>

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


 Description

    msgctl provides a variety of message control operations as specified by
    cmd.  The operations are performed on the current host (as specified in
    the most recent dflthost call).  The following cmds are available:

    IPCSTAT  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(PCI).

    IPCSET   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 low nine bits */
                 msg_qbytes


    This cmd can only be executed by a process with an effective user ID
    equal to either the super-user or the value of msgperm.[c]uid in the
    data structure associated with msqid.  Only the super-user can raise the
    value of msgqbytes.

    IPCRMID  Remove the message queue identifier specified by msqid from the
              UNIX operating 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
              super-user or to the value of msgperm.[c]uid in the data
              structure associated with msqid.

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

    [EINVAL]  msqid is not a valid message queue identifier.

    [EINVAL]  cmd is not a valid command.

    [EACCES]  cmd is equal to IPCSTAT and read operation permission is
              denied to the calling process (see Intro(PCI).

    [EPERM]   cmd is equal to IPCRMID or IPCSET, and the effective user ID
              of the calling process is not equal to that of super-user and
              is not equal to the value of msgperm.[c]uid in the data struc-
              ture associated with msqid.

    [EPERM]   cmd is equal to IPCSET, an attempt is being made to increase
              to the value of msgqbytes, and the effective user ID of the
              calling process is not equal to that of super-user.

    [EFAULT]  buf points to an illegal address.


 Return value

    On successful completion, a value of 0 returns.  If the call fails for
    any reason, a value of -1 returns and errno is set to indicate the error.

 See also

    dflthost(PCI), Intro(PCI), msgget(PCI), msgrcv(PCI), msgsnd(PCI)