VMS Help System Services, $CREMBX  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Creates a virtual mailbox device named MBAn and assigns an I/O
    channel to it. The system provides the unit number n when it
    creates the mailbox. If a logical name is specified and a mailbox
    with the specified name already exists, the $CREMBX service
    assigns a channel to the existing mailbox.

    Format

      SYS$CREMBX  [prmflg] ,chan ,[maxmsg] ,[bufquo] ,[promsk]

                  ,[acmode] ,[lognam] ,[flags] ,[nullarg]

    C Prototype

      int sys$crembx  (char prmflg, unsigned short int *chan,

                      unsigned int maxmsg, unsigned int bufquo,

                      unsigned int promsk, unsigned int acmode, void

                      *lognam,...);

1 - Arguments

 prmflg

    OpenVMS usage:boolean
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Indicator specifying whether the created mailbox is to be
    permanent or temporary. The prmflg argument is a longword value.
    The value 1 specifies a permanent mailbox; the value 0, which
    is the default, specifies a temporary mailbox. Any other values
    result in an error.

 chan

    OpenVMS usage:channel
    type:         word
    access:       write only
    mechanism:    by reference
    Channel number assigned by $CREMBX to the mailbox. The chan
    argument is the address of a word into which $CREMBX writes the
    channel number.

 maxmsg

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Maximum size (in bytes) of a message that can be sent to the
    mailbox. The maxmsg argument is a longword value containing this
    size.

    The maximum value you can specify for the maxmsg argument is
    65535. If you do not specify a value or specify the value as 0,
    the operating system provides a default value.

 bufquo

    OpenVMS usage:longword_unsigned
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Number of bytes of system dynamic memory that can be used to
    buffer messages sent to the mailbox. The bufquo argument is a
    word value containing this number. If you do not specify the
    bufquo argument or specify it as 0, the operating system provides
    a default value.

    The maximum value that you can specify with the bufquo argument
    is 60000. For a temporary mailbox, this value must be less than
    or equal to the process buffer quota.

 promsk

    OpenVMS usage:file_protection
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Protection mask to be associated with the created mailbox. The
    promsk argument is a longword value that is the combined value
    of the bits set in the protection mask. Cleared bits grant access
    and set bits deny access to each of the four classes of user:
    world, group, owner, and system. The following diagram depicts
    these protection bits:

            |------------|------------|------------|------------|
            |   World    |    Group   |   Owner    |   System   |
            |------------|------------|------------|------------|
            | L  P  W  R | L  P  W  R | L  P  W  R | L  P  W  R |
            |------------|------------|------------|------------|
             15 14 13 12  11 10  9  8   7  6  5  4   3  2  1  0

    If you do not specify the promsk argument or specify it as 0, the
    mailbox template is used.

    The logical access bit must be clear for the class of user
    requiring access to the mailbox. The access bit must be clear
    for all categories of user because logical access is required to
    read or write to a mailbox; thus, setting or clearing the read
    and write access bits is meaningless unless the logical access
    bit is also cleared.

    The physical access bit is ignored for all categories of user.

    Logical access also allows you to queue read or write attention
    ASTs.

 acmode

    OpenVMS usage:access_mode
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Access mode to be associated with the channel to which the
    mailbox is assigned. The acmode argument is a longword containing
    the access mode.

    The $PSLDEF macro defines the following symbols for the four
    access modes:

    Symbol         Access Mode    Numeric Value

    PSL$C_KERNEL   Kernel         0
    PSL$C_EXEC     Executive      1
    PSL$C_SUPER    Supervisor     2
    PSL$C_USER     User           3

    The most privileged access mode used is the access mode of
    the caller. The specified access mode and the access mode of
    the caller are compared. The less privileged (but the higher
    numeric valued) of the two access modes becomes the access
    mode associated with the assigned channel. I/O operations on
    the channel can be performed only from equal or more privileged
    access modes.

 lognam

    OpenVMS usage:logical_name
    type:         character-coded text string
    access:       read only
    mechanism:    by descriptor-fixed-length string descriptor
    Logical name to be assigned to the mailbox. The lognam argument
    is the address of a character string descriptor pointing to the
    logical name string.

    The equivalence name for the mailbox is MBAn. The equivalence
    name is marked with the terminal attribute. Processes can use the
    logical name to assign other I/O channels to the mailbox.

    For permanent mailboxes, the $CREMBX service enters the specified
    logical name, if any, in the LNM$PERMANENT_MAILBOX logical name
    table and, for temporary mailboxes, into the LNM$TEMPORARY_
    MAILBOX logical name table.

    You can specify any name from 1 to 43 characters. All processes
    mapping to the same global section must specify the same name.
    Note that the name is case sensitive.

    Use of characters valid in logical names is strongly encouraged.
    Valid values include alphanumeric characters, the dollar sign
    ($), and the underscore (_). If the name string begins with an
    underscore (_), the underscore is stripped and the resultant
    string is considered to be the actual name. Use of the colon (:)
    is not permitted.

    Names are first subject to a logical name translation, after
    the application of the prefix GBL$ to the name. If the result
    translates, it is used as the name of the section. If the
    resulting name does not translate, the name specified by the
    caller is used as the name of the section.

    Additional information on logical name translations and on
    section name processing is available in the OpenVMS Programming
    Concepts Manual.

 flags

    OpenVMS usage:mask_longword
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    The flags argument is used for specifying options for the
    assign operation that occurs in $CREMBX. The flags argument
    is a longword bit mask that enables the user to specify that
    the channel assigned to the mailbox is a READ ONLY or WRITE
    ONLY channel. If the flags argument is not specified, then the
    default channel behavior is READ/WRITE. The $CMBDEF macro defines
    a symbolic name for each flag bit.

    The following table describes each flag:

    Flag            Description

    CMB$M_          When this flag is specified, $CREMBX assigns
    READONLY        a read-only channel to the mailbox device.
                    An attempt to issue a QIO WRITE operation on
                    the mailbox channel results in an illegal I/O
                    operation error.
    CMB$M_          When this flag is specified, $CREMBX assigns
    WRITEONLY       a write-only channel to the mailbox device.
                    An attempt to issue a QIO READ operation on
                    the mailbox channel results in an illegal I/O
                    operation error.

    For more information about the flags argument, refer to the
    OpenVMS I/O User's Reference Manual.

 nullarg

    OpenVMS usage:null_arg
    type:         longword (unsigned)
    access:       read only
    mechanism:    by value
    Placeholding argument reserved by Compaq.