Tribblix: manual page: putmsg.2

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.