PUTMSG(3P) POSIX Programmer's Manual PUTMSG(3P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the correspond-
ing 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 struc-
ture.
The ctlptr argument points to the structure describing the control part, if any, to be included in the message. The buf member in the str-
buf 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
None.
SEE ALSO
STREAMS, getmsg(), poll(), read(), write(), the Base Definitions volume of IEEE Std 1003.1-2001, <stropts.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .
IEEE
/The Open Group 2003 PUTMSG(3P)