PUTMSG(P) POSIX Programmer's Manual PUTMSG(P)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 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 mes‐
sage. 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 (con‐
trol) 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 [EIN‐
VAL]. 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 condi‐
tion 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; oth‐
erwise, 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 config‐
ured 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, respec‐
tively.
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 exam‐
ple, 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 Technology
-- 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(P)
