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PROLOG

       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

       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 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

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

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

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2013 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX),  The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/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 .