PUTMSG(2)PUTMSG(2)NAME
putmsg, putpmsg - send a message on a stream
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 creates a message 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.
The putpmsg() function does the same thing as putmsg(), but provides
the user the ability to send messages in different priority bands.
Except where noted, all information pertaining to putmsg() also per‐
tains 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, which contains the following members:
int maxlen; /* not used here */
int len; /* length of data */
void *buf; /* ptr to buffer */
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 in putmsg() (see getmsg(2)). In a similar
manner, 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 later.
To send the data part of a message, dataptr must not be NULL, and the
len member 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 is sent if either dataptr (ctlptr) is
NULL or the len member of dataptr (ctlptr) is negative.
For putmsg(), if a control part is specified, and flags is set to
RS_HIPRI, a high priority message is sent. If no control part is speci‐
fied, and flags is set to RS_HIPRI, putmsg() fails and sets errno to
EINVAL. If flags is set to 0, a normal (non-priority) message is sent.
If no control part and no data part are specified, and flags is set to
0, no message is sent, and 0 is returned.
The stream head guarantees that the control part of a message generated
by putmsg() is at least 64 bytes in length.
For putpmsg(), the flags are different. The flags argument is a bit‐
mask with the following mutually-exclusive flags defined: MSG_HIPRI and
MSG_BAND. If flags is set to 0, putpmsg() fails and sets errno to EIN‐
VAL. If a control part is specified and flags is set to MSG_HIPRI and
band is set to 0, a high-priority message is 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() fails and sets errno to EINVAL. If flags is
set to MSG_BAND, then a message is 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 is sent and 0 is returned.
Normally, putmsg() will block if the stream write queue is full due to
internal flow control conditions. For high-priority messages, putmsg()
does not block on this condition. For other messages, putmsg() does
not block when the write queue is full and O_NDELAY or O_NONBLOCK is
set. Instead, it fails and sets errno to EAGAIN.
The putmsg() or putpmsg() function also blocks, unless prevented by
lack of internal resources, waiting for the availability of message
blocks in the stream, regardless of priority or whether O_NDELAY or
O_NONBLOCK has been specified. No partial message is sent.
RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, −1 is returned
and errno is set to indicate the error.
ERRORS
The putmsg() and putpmsg() functions will fail if:
EAGAIN
A non-priority message was specified, the O_NDELAY or
O_NONBLOCK flag is set and the stream write queue is
full due to internal flow control conditions.
EBADF
The fildes argument is not a valid file descriptor open
for writing.
EFAULT
The ctlptr or dataptr argument points to an illegal
address.
EINTR
A signal was caught during the execution of the
putmsg() function.
EINVAL
An undefined value was specified in flags; flags is set
to RS_HIPRI and no control part was supplied; or the
stream referenced by fildes is linked below a multi‐
plexor.
ENOSR
Buffers could not be allocated for the message that was
to be created due to insufficient streams memory
resources.
ENOSTR
The fildes argument is not associated with a stream.
ENXIO
A hangup condition was generated downstream for the
specified stream, or the other end of the pipe is
closed.
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. This error condi‐
tion occurs only with SUS-conforming applications. See
standards(5).
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() will 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 putpmsg() function will fail if:
EINVAL
The flags argument is set to MSG_HIPRI and band is non-zero.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬─────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼─────────────────┤
│Interface Stability │ Standard │
└────────────────────┴─────────────────┘
SEE ALSOIntro(2), getmsg(2), poll(2), read(2), write(2), attributes(5), stan‐
dards(5)
STREAMS Programming Guide
Nov 1, 2003 PUTMSG(2)
