1PUTMSG(P) POSIX Programmer's Manual PUTMSG(P)
2
6 putmsg, putpmsg - send a message on a STREAM (STREAMS)
7
9 #include <stropts.h>
10 int putmsg(int fildes, const struct strbuf *ctlptr,
12 const struct strbuf *dataptr, int flags);
13 int putpmsg(int fildes, const struct strbuf *ctlptr,
14 const struct strbuf *dataptr, int band, int flags);
15
18 The putmsg() function shall create a message from a process buffer(s)
19 and send the message to a STREAMS file. The message may contain either
20 a data part, a control part, or both. The data and control parts are
21 distinguished by placement in separate buffers, as described below. The
22 semantics of each part are defined by the STREAMS module that receives
23 the message.
24 The putpmsg() function is equivalent to putmsg(), except that the
26 process can send messages in different priority bands. Except where
27 noted, all requirements on putmsg() also pertain to putpmsg().
28 The fildes argument specifies a file descriptor referencing an open
30 STREAM. The ctlptr and dataptr arguments each point to a strbuf struc‐
31 ture.
32 The ctlptr argument points to the structure describing the control
34 part, if any, to be included in the message. The buf member in the str‐
35 buf structure points to the buffer where the control information
36 resides, and the len member indicates the number of bytes to be sent.
37 The maxlen member is not used by putmsg(). In a similar manner, the
38 argument dataptr specifies the data, if any, to be included in the mes‐
39 sage. The flags argument indicates what type of message should be sent
40 and is described further below.
41 To send the data part of a message, the application shall ensure that
43 dataptr is not a null pointer and the len member of dataptr is 0 or
44 greater. To send the control part of a message, the application shall
45 ensure that the corresponding values are set for ctlptr. No data (con‐
46 trol) part shall be sent if either dataptr( ctlptr) is a null pointer
47 or the len member of dataptr( ctlptr) is set to -1.
48 For putmsg(), if a control part is specified and flags is set to
50 RS_HIPRI, a high priority message shall be sent. If no control part is
51 specified, and flags is set to RS_HIPRI, putmsg() shall fail and set
52 errno to [EINVAL]. If flags is set to 0, a normal message (priority
53 band equal to 0) shall be sent. If a control part and data part are not
54 specified and flags is set to 0, no message shall be sent and 0 shall
55 be returned.
56 For putpmsg(), the flags are different. The flags argument is a bitmask
58 with the following mutually-exclusive flags defined: MSG_HIPRI and
59 MSG_BAND. If flags is set to 0, putpmsg() shall fail and set errno to
60 [EINVAL]. If a control part is specified and flags is set to MSG_HIPRI
61 and band is set to 0, a high-priority message shall be sent. If flags
62 is set to MSG_HIPRI and either no control part is specified or band is
63 set to a non-zero value, putpmsg() shall fail and set errno to [EIN‐
64 VAL]. If flags is set to MSG_BAND, then a message shall be sent in the
65 priority band specified by band. If a control part and data part are
66 not specified and flags is set to MSG_BAND, no message shall be sent
67 and 0 shall be returned.
68 The putmsg() function shall block if the STREAM write queue is full due
70 to internal flow control conditions, with the following exceptions:
71 * For high-priority messages, putmsg() shall not block on this condi‐
73 tion and continues processing the message.
74 * For other messages, putmsg() shall not block but shall fail when the
76 write queue is full and O_NONBLOCK is set.
77 The putmsg() function shall also block, unless prevented by lack of
79 internal resources, while waiting for the availability of message
80 blocks in the STREAM, regardless of priority or whether O_NONBLOCK has
81 been specified. No partial message shall be sent.
82
84 Upon successful completion, putmsg() and putpmsg() shall return 0; oth‐
85 erwise, they shall return -1 and set errno to indicate the error.
86
88 The putmsg() and putpmsg() functions shall fail if:
89 EAGAIN A non-priority message was specified, the O_NONBLOCK flag is
91 set, and the STREAM write queue is full due to internal flow
92 control conditions; or buffers could not be allocated for the
93 message that was to be created.
94 EBADF fildes is not a valid file descriptor open for writing.
96 EINTR A signal was caught during putmsg().
98 EINVAL An undefined value is specified in flags, or flags is set to
100 RS_HIPRI or MSG_HIPRI and no control part is supplied, or the
101 STREAM or multiplexer referenced by fildes is linked (directly
102 or indirectly) downstream from a multiplexer, or flags is set to
103 MSG_HIPRI and band is non-zero (for putpmsg() only).
104 ENOSR Buffers could not be allocated for the message that was to be
106 created due to insufficient STREAMS memory resources.
107 ENOSTR A STREAM is not associated with fildes.
109 ENXIO A hangup condition was generated downstream for the specified
111 STREAM.
112 EPIPE or EIO
114 The fildes argument refers to a STREAMS-based pipe and the other
115 end of the pipe is closed. A SIGPIPE signal is generated for the
116 calling thread.
117 ERANGE The size of the data part of the message does not fall within
119 the range specified by the maximum and minimum packet sizes of
120 the topmost STREAM module. This value is also returned if the
121 control part of the message is larger than the maximum config‐
122 ured size of the control part of a message, or if the data part
123 of a message is larger than the maximum configured size of the
124 data part of a message.
125 In addition, putmsg() and putpmsg() shall fail if the STREAM head had
128 processed an asynchronous error before the call. In this case, the
129 value of errno does not reflect the result of putmsg() or putpmsg(),
130 but reflects the prior error.
131 The following sections are informative.
133
135 Sending a High-Priority Message
136 The value of fd is assumed to refer to an open STREAMS file. This call
137 to putmsg() does the following:
138 1. Creates a high-priority message with a control part and a data
140 part, using the buffers pointed to by ctrlbuf and databuf, respec‐
141 tively.
142 2. Sends the message to the STREAMS file identified by fd.
144 #include <stropts.h>
146 #include <string.h>
147 ...
148 int fd;
149 char *ctrlbuf = "This is the control part";
150 char *databuf = "This is the data part";
151 struct strbuf ctrl;
152 struct strbuf data;
153 int ret;
154 ctrl.buf = ctrlbuf;
157 ctrl.len = strlen(ctrlbuf);
158 data.buf = databuf;
161 data.len = strlen(databuf);
162 ret = putmsg(fd, &ctrl, &data, MSG_HIPRI);
165 Using putpmsg()
167 This example has the same effect as the previous example. In this exam‐
168 ple, however, the putpmsg() function creates and sends the message to
169 the STREAMS file.
170 #include <stropts.h>
173 #include <string.h>
174 ...
175 int fd;
176 char *ctrlbuf = "This is the control part";
177 char *databuf = "This is the data part";
178 struct strbuf ctrl;
179 struct strbuf data;
180 int ret;
181 ctrl.buf = ctrlbuf;
184 ctrl.len = strlen(ctrlbuf);
185 data.buf = databuf;
188 data.len = strlen(databuf);
189 ret = putpmsg(fd, &ctrl, &data, 0, MSG_HIPRI);
192
194 None.
195
197 None.
198
200 None.
201
203 STREAMS , getmsg() , poll() , read() , write() , the Base Definitions
204 volume of IEEE Std 1003.1-2001, <stropts.h>
205
207 Portions of this text are reprinted and reproduced in electronic form
208 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
209 -- Portable Operating System Interface (POSIX), The Open Group Base
210 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
211 Electrical and Electronics Engineers, Inc and The Open Group. In the
212 event of any discrepancy between this version and the original IEEE and
213 The Open Group Standard, the original IEEE and The Open Group Standard
214 is the referee document. The original Standard can be obtained online
215 at http://www.opengroup.org/unix/online.html .
216IEEE/The Open Group 2003 PUTMSG(P)