PUTMSG(3)                  POSIX Programmer's Manual                 PUTMSG(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       putmsg, putpmsg -- send a message on a STREAM (STREAMS)

SYNOPSIS
       #include <stropts.h>

       int putmsg(int fildes, const struct strbuf *ctlptr,
           const struct strbuf *dataptr, int flags);
       int putpmsg(int fildes, const struct strbuf *ctlptr,
           const struct strbuf *dataptr, int band, int flags);

DESCRIPTION
       The putmsg() function shall create a message from a process buffer(s)
       and send the message to a STREAMS file. The message may contain either
       a data part, a control part, or both. The data and control parts are
       distinguished by placement in separate buffers, as described below. The
       semantics of each part are defined by the STREAMS module that receives
       the message.

       The putpmsg() function is equivalent to putmsg(), except that the
       process can send messages in different priority bands.  Except where
       noted, all requirements on putmsg() also pertain to putpmsg().

       The fildes argument specifies a file descriptor referencing an open
       STREAM. The ctlptr and dataptr arguments each point to a strbuf
       structure.

       The ctlptr argument points to the structure describing the control
       part, if any, to be included in the message. The buf member in the
       strbuf structure points to the buffer where the control information
       resides, and the len member indicates the number of bytes to be sent.
       The maxlen member is not used by putmsg().  In a similar manner, the
       argument dataptr specifies the data, if any, to be included in the
       message. The flags argument indicates what type of message should be
       sent and is described further below.

       To send the data part of a message, the application shall ensure that
       dataptr is not a null pointer and the len member of dataptr is 0 or
       greater. To send the control part of a message, the application shall
       ensure that the corresponding values are set for ctlptr.  No data
       (control) part shall be sent if either dataptr(ctlptr) is a null
       pointer or the len member of dataptr(ctlptr) is set to -1.

       For putmsg(), if a control part is specified and flags is set to
       RS_HIPRI, a high priority message shall be sent. If no control part is
       specified, and flags is set to RS_HIPRI, putmsg() shall fail and set
       errno to [EINVAL].  If flags is set to 0, a normal message (priority
       band equal to 0) shall be sent.  If a control part and data part are
       not specified and flags is set to 0, no message shall be sent and 0
       shall be returned.

       For putpmsg(), the flags are different. The flags argument is a bitmask
       with the following mutually-exclusive flags defined: MSG_HIPRI and
       MSG_BAND. If flags is set to 0, putpmsg() shall fail and set errno to
       [EINVAL].  If a control part is specified and flags is set to MSG_HIPRI
       and band is set to 0, a high-priority message shall be sent. If flags
       is set to MSG_HIPRI and either no control part is specified or band is
       set to a non-zero value, putpmsg() shall fail and set errno to
       [EINVAL].  If flags is set to MSG_BAND, then a message shall be sent in
       the priority band specified by band.  If a control part and data part
       are not specified and flags is set to MSG_BAND, no message shall be
       sent and 0 shall be returned.

       The putmsg() function shall block if the STREAM write queue is full due
       to internal flow control conditions, with the following exceptions:

        *  For high-priority messages, putmsg() shall not block on this
           condition and continues processing the message.

        *  For other messages, putmsg() shall not block but shall fail when
           the write queue is full and O_NONBLOCK is set.

       The putmsg() function shall also block, unless prevented by lack of
       internal resources, while waiting for the availability of message
       blocks in the STREAM, regardless of priority or whether O_NONBLOCK has
       been specified. No partial message shall be sent.

RETURN VALUE
       Upon successful completion, putmsg() and putpmsg() shall return 0;
       otherwise, they shall return -1 and set errno to indicate the error.

ERRORS
       The putmsg() and putpmsg() functions shall fail if:

       EAGAIN A non-priority message was specified, the O_NONBLOCK flag is
              set, and the STREAM write queue is full due to internal flow
              control conditions; or buffers could not be allocated for the
              message that was to be created.

       EBADF  fildes is not a valid file descriptor open for writing.

       EINTR  A signal was caught during putmsg().

       EINVAL An undefined value is specified in flags, or flags is set to
              RS_HIPRI or MSG_HIPRI and no control part is supplied, or the
              STREAM or multiplexer referenced by fildes is linked (directly
              or indirectly) downstream from a multiplexer, or flags is set to
              MSG_HIPRI and band is non-zero (for putpmsg() only).

       ENOSR  Buffers could not be allocated for the message that was to be
              created due to insufficient STREAMS memory resources.

       ENOSTR A STREAM is not associated with fildes.

       ENXIO  A hangup condition was generated downstream for the specified
              STREAM.

       EPIPE or EIO
              The fildes argument refers to a STREAMS-based pipe and the other
              end of the pipe is closed. A SIGPIPE signal is generated for the
              calling thread.

       ERANGE The size of the data part of the message does not fall within
              the range specified by the maximum and minimum packet sizes of
              the topmost STREAM module. This value is also returned if the
              control part of the message is larger than the maximum
              configured size of the control part of a message, or if the data
              part of a message is larger than the maximum configured size of
              the data part of a message.

       In addition, putmsg() and putpmsg() shall fail if the STREAM head had
       processed an asynchronous error before the call. In this case, the
       value of errno does not reflect the result of putmsg() or putpmsg(),
       but reflects the prior error.

       The following sections are informative.

EXAMPLES
   Sending aa High-Priority Message
       The value of fd is assumed to refer to an open STREAMS file. This call
       to putmsg() does the following:

        1. Creates a high-priority message with a control part and a data
           part, using the buffers pointed to by ctrlbuf and databuf,
           respectively.

        2. Sends the message to the STREAMS file identified by fd.


           #include <stropts.h>
           #include <string.h>
           ...
           int fd;
           char *ctrlbuf = "This is the control part";
           char *databuf = "This is the data part";
           struct strbuf ctrl;
           struct strbuf data;
           int ret;

           ctrl.buf = ctrlbuf;
           ctrl.len = strlen(ctrlbuf);

           data.buf = databuf;
           data.len = strlen(databuf);

           ret = putmsg(fd, &ctrl, &data, MSG_HIPRI);

   Using putpmsg()
       This example has the same effect as the previous example. In this
       example, however, the putpmsg() function creates and sends the message
       to the STREAMS file.


           #include <stropts.h>
           #include <string.h>
           ...
           int fd;
           char *ctrlbuf = "This is the control part";
           char *databuf = "This is the data part";
           struct strbuf ctrl;
           struct strbuf data;
           int ret;

           ctrl.buf = ctrlbuf;
           ctrl.len = strlen(ctrlbuf);

           data.buf = databuf;
           data.len = strlen(databuf);

           ret = putpmsg(fd, &ctrl, &data, 0, MSG_HIPRI);

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       The putmsg() and putpmsg() functions may be removed in a future
       version.

SEE ALSO
       Section 2.6, STREAMS, getmsg(), poll(), read(), write()

       The Base Definitions volume of POSIX.1-2017, <stropts.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                            PUTMSG(3)
