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putmsg.3p (9149B)

'\" et
.TH PUTMSG "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH 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.
.\"
.SH NAME
putmsg,
putpmsg
\(em send a message on a STREAM (\fBSTREAMS\fP)
.SH SYNOPSIS
.LP
.nf
#include <stropts.h>
.P
int putmsg(int \fIfildes\fP, const struct strbuf *\fIctlptr\fP,
    const struct strbuf *\fIdataptr\fP, int \fIflags\fP);
int putpmsg(int \fIfildes\fP, const struct strbuf *\fIctlptr\fP,
    const struct strbuf *\fIdataptr\fP, int \fIband\fP, int \fIflags\fP);
.fi
.SH DESCRIPTION
The
\fIputmsg\fR()
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.
.P
The
\fIputpmsg\fR()
function is equivalent to
\fIputmsg\fR(),
except that the process can send messages in different priority bands.
Except where noted, all requirements on
\fIputmsg\fR()
also pertain to
\fIputpmsg\fR().
.P
The
.IR fildes
argument specifies a file descriptor referencing an open STREAM. The
.IR ctlptr
and
.IR dataptr
arguments each point to a
.BR strbuf
structure.
.P
The
.IR ctlptr
argument points to the structure describing the control part, if any,
to be included in the message. The
.IR buf
member in the
.BR strbuf
structure points to the buffer where the control information resides,
and the
.IR len
member indicates the number of bytes to be sent. The
.IR maxlen
member is not used by
\fIputmsg\fR().
In a similar manner, the argument
.IR dataptr
specifies the data, if any, to be included in the message. The
.IR flags
argument indicates what type of message should be sent and is described
further below.
.P
To send the data part of a message, the application shall ensure that
.IR dataptr
is not a null pointer and the
.IR len
member of
.IR dataptr
is 0 or greater. To send the control part of a message, the application
shall ensure that the corresponding values are set for
.IR ctlptr .
No data (control) part shall be sent if either
.IR dataptr (\c
.IR ctlptr )
is a null pointer or the
.IR len
member of
.IR dataptr (\c
.IR ctlptr )
is set to \-1.
.P
For
\fIputmsg\fR(),
if a control part is specified and
.IR flags
is set to RS_HIPRI, a high
priority message shall be sent. If no control part is specified, and
.IR flags
is set to RS_HIPRI,
\fIputmsg\fR()
shall fail and set
.IR errno
to
.BR [EINVAL] .
If
.IR 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
.IR flags
is set to 0, no message shall be sent and 0 shall be returned.
.P
For
\fIputpmsg\fR(),
the flags are different. The
.IR flags
argument is a bitmask with the following mutually-exclusive flags
defined: MSG_HIPRI and MSG_BAND. If
.IR flags
is set to 0,
\fIputpmsg\fR()
shall fail and set
.IR errno
to
.BR [EINVAL] .
If a control part is specified and
.IR flags
is set to MSG_HIPRI and
.IR band
is set to 0, a high-priority message shall be sent. If
.IR flags
is set to MSG_HIPRI and either no control part is specified or
.IR band
is set to a non-zero value,
\fIputpmsg\fR()
shall fail and set
.IR errno
to
.BR [EINVAL] .
If
.IR flags
is set to MSG_BAND, then a message shall be sent in the priority band
specified by
.IR band .
If a control part and data part are not specified and
.IR flags
is set to MSG_BAND, no message shall be sent and 0 shall be returned.
.br
.P
The
\fIputmsg\fR()
function shall block if the STREAM write queue is full due to internal
flow control conditions, with the following exceptions:
.IP " *" 4
For high-priority messages,
\fIputmsg\fR()
shall not block on this condition and continues processing the message.
.IP " *" 4
For other messages,
\fIputmsg\fR()
shall not block but shall fail when the write queue is full and
O_NONBLOCK is set.
.P
The
\fIputmsg\fR()
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.
.SH "RETURN VALUE"
Upon successful completion,
\fIputmsg\fR()
and
\fIputpmsg\fR()
shall return 0; otherwise, they shall return \-1 and set
.IR errno
to indicate the error.
.SH ERRORS
The
\fIputmsg\fR()
and
\fIputpmsg\fR()
functions shall fail if:
.TP
.BR 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.
.TP
.BR EBADF
.IR fildes
is not a valid file descriptor open for writing.
.TP
.BR EINTR
A signal was caught during
\fIputmsg\fR().
.TP
.BR EINVAL
An undefined value is specified in
.IR flags ,
or
.IR flags
is set to RS_HIPRI or MSG_HIPRI and no control part is supplied, or the
STREAM or multiplexer referenced by
.IR fildes
is linked (directly or indirectly) downstream from a multiplexer, or
.IR flags
is set to MSG_HIPRI and
.IR band
is non-zero (for
\fIputpmsg\fR()
only).
.TP
.BR ENOSR
Buffers could not be allocated for the message that was to be created
due to insufficient STREAMS memory resources.
.TP
.BR ENOSTR
A STREAM is not associated with
.IR fildes .
.TP
.BR ENXIO
A hangup condition was generated downstream for the specified STREAM.
.TP
.BR EPIPE " or " EIO
The
.IR 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.
.TP
.BR 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.
.P
In addition,
\fIputmsg\fR()
and
\fIputpmsg\fR()
shall fail if the STREAM head had processed an asynchronous error
before the call. In this case, the value of
.IR errno
does not reflect the result of
\fIputmsg\fR()
or
\fIputpmsg\fR(),
but reflects the prior error.
.br
.LP
.IR "The following sections are informative."
.SH EXAMPLES
.SS "Sending a High-Priority Message"
.P
The value of
.IR fd
is assumed to refer to an open STREAMS file. This call to
\fIputmsg\fR()
does the following:
.IP " 1." 4
Creates a high-priority message with a control part and a data part,
using the buffers pointed to by
.IR ctrlbuf
and
.IR databuf ,
respectively.
.IP " 2." 4
Sends the message to the STREAMS file identified by
.IR fd .
.sp
.RS 4
.nf
#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;
.P
ctrl.buf = ctrlbuf;
ctrl.len = strlen(ctrlbuf);
.P
data.buf = databuf;
data.len = strlen(databuf);
.P
ret = putmsg(fd, &ctrl, &data, MSG_HIPRI);
.fi
.P
.RE
.SS "Using putpmsg(\|)"
.P
This example has the same effect as the previous example. In this
example, however, the
\fIputpmsg\fR()
function creates and sends the message to the STREAMS file.
.sp
.RS 4
.nf
#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;
.P
ctrl.buf = ctrlbuf;
ctrl.len = strlen(ctrlbuf);
.P
data.buf = databuf;
data.len = strlen(databuf);
.P
ret = putpmsg(fd, &ctrl, &data, 0, MSG_HIPRI);
.fi
.P
.RE
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
The
\fIputmsg\fR()
and
\fIputpmsg\fR()
functions may be removed in a future version.
.SH "SEE ALSO"
.IR "Section 2.6" ", " "STREAMS",
.IR "\fIgetmsg\fR\^(\|)",
.IR "\fIpoll\fR\^(\|)",
.IR "\fIread\fR\^(\|)",
.IR "\fIwrite\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<stropts.h>\fP"
.\"
.SH COPYRIGHT
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 .
.PP
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 .