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PUTMSG(2)                     System Calls Manual                    PUTMSG(2)



NAME
       putmsg - send a message on a stream

SYNOPSIS
       #include <&lt;stropts.h>&gt;

       int putmsg(fd, ctlptr, dataptr, flags)
       int fd;
       struct strbuf *ctlptr;
       struct strbuf *dataptr;
       int flags;

DESCRIPTION
       putmsg() creates a message (see intro(2)) from user specified buffer(s)
       and sends the message to a  STREAMS  file.   The  message  may  contain
       either a data part, a control part or both.  The data and control parts
       to be sent are distinguished  by  placement  in  separate  buffers,  as
       described  below.  The semantics of each part is defined by the STREAMS
       module that receives the message.

       fd specifies a file descriptor referencing an open stream.  ctlptr  and
       dataptr  each  point  to a strbuf structure that contains the following
       members:

              int maxlen;      /* not used */
              int len;         /* length of data */
              char *buf;       /* ptr to buffer */

       ctlptr points to the structure describing the control part, if any,  to
       be  included  in  the  message.   The buf field in the strbuf structure
       points to the buffer where the control information resides, and the len
       field  indicates  the  number of bytes to be sent.  The maxlen field is
       not used in putmsg() (see getmsg(2)).  In  a  similar  manner,  dataptr
       specifies  the  data, if any, to be included in the message.  flags may
       be set to the values 0 or RS_HIPRI and is used as described below.

       To send the data part of a message, dataptr must not be a NULL  pointer
       and  the  len  field  of dataptr must have a value of 0 or greater.  To
       send the control part of a message, the corresponding  values  must  be
       set  for ctlptr.  No data (control) part will be sent if either dataptr
       (ctlptr) is a NULL pointer or the len field of dataptr (ctlptr) is  set
       to -1.

       If  a control part is specified, and flags is set to RS_HIPRI, a prior-
       ity message is sent.  If flags is set to 0, a non-priority  message  is
       sent.   If  no control part is specified, and flags is set to RS_HIPRI,
       putmsg() fails and sets errno to EINVAL.  If no  control  part  and  no
       data part are specified, and flags is set to 0, no message is sent, and
       0 is returned.

       For non-priority messages, putmsg() will  block  if  the  stream  write
       queue  is  full  due to internal flow control conditions.  For priority
       messages, putmsg() does not block on this condition.  For  non-priority
       messages,  putmsg()  does  not  block  when the write queue is full and
       O_NDELAY is set.  Instead, it fails and sets errno to EAGAIN.

       putmsg() also blocks, unless prevented by lack of  internal  resources,
       waiting  for  the availability of message blocks in the stream, regard-
       less of priority or whether O_NDELAY has been  specified.   No  partial
       message is sent.

RETURN VALUES
       putmsg() returns:

       0      on success.

       -1     on failure and sets errno to indicate the error.

ERRORS
       EAGAIN         A  non-priority message was specified, the O_NDELAY flag
                      is set and the stream write queue is full due to  inter-
                      nal flow control conditions.

                      Buffers  could not be allocated for the message that was
                      to be created.

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

       EFAULT         ctlptr or dataptr points outside the  allocated  address
                      space.

       EINTR          A signal was caught during the putmsg() system call.

       EINVAL         An undefined value was specified in flags.

                      flags  is  set  to RS_HIPRI and no control part was sup-
                      plied.

                      The stream referenced by fd is  linked  below  a  multi-
                      plexor.

       ENOSTR         A stream is not associated with fd.

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

       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.

                      The control part of the message is larger than the maxi-
                      mum configured size of the control part of a message.

                      The  data part of the message is larger than the maximum
                      configured size of the data part of a message.

       A putmsg() also fails if a STREAMS error message had been processed  by
       the stream head before the call to putmsg().  The error returned is the
       value contained in the STREAMS error message.

SEE ALSO
       getmsg(2), intro(2), poll(2), read(2V), write(2V)



                                21 January 1990                      PUTMSG(2)