putmsg(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

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

NAME         top

       putmsg, putpmsg — send a message on a STREAM (STREAMS)

SYNOPSIS         top

       #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         top

       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         top

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

ERRORS         top

       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         top

   Sending a 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         top

       None.

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

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

SEE ALSO         top

       Section 2.6, STREAMS, getmsg(3p), poll(3p), read(3p), write(3p)

       The Base Definitions volume of POSIX.1‐2017, stropts.h(0p)

COPYRIGHT         top

       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(3P)

Pages that refer to this page: stropts.h(0p)getmsg(3p)ioctl(3p)poll(3p)