PUTMSG(2) System Calls 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 pertains to
putpmsg().
The
fildes argument specifies a file descriptor referencing an open
stream. The
ctlptr and
dataptr arguments each point to a
strbuf structure, 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
strbuf 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 message. 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
specified, 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 bitmask
with the following mutually-exclusive flags defined:
MSG_HIPRI and
MSG_BAND. If
flags is set to 0,
putpmsg() fails and sets
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 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
multiplexor.
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 condition
occurs only with SUS-conforming applications. See
standards(7).
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(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
SEE ALSO
Intro(2),
getmsg(2),
poll(2),
read(2),
write(2),
attributes(7),
standards(7) STREAMS Programming Guide November 1, 2003
PUTMSG(2)