PUTMSG(2)

NAME
putmsg - send a message on a stream

SYNOPSIS
#include <stropts.h>

int putmsg(fd, ctlptr, dataptr, flags)
int fd;
struct strbuf *ctlptr;
struct strbuf *dataptr;
int flags;

DESCRIPTION

putmsg() creates a message (see intro(2)) 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.

fd specifies a file descriptor referencing an open stream. ctlptr and dataptr each point to a strbuf structure that contains the following members:

    int maxlen;	/* not used */
    int len;  	/* length of data */
    char *buf;	/* ptr to buffer */

ctlptr points to the structure describing the control part, if any, to be included in the message. The buf field in the strbuf structure points to the buffer where the control information resides, and the len field indicates the number of bytes to be sent. The maxlen field is not used in putmsg() (see getmsg(2)). In a similar manner, dataptr specifies the data, if any, to be included in the message. flags may be set to the values 0 or RS_HIPRI and is used as described below.

To send the data part of a message, dataptr must not be a NULL pointer and the len field 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 will be sent if either dataptr (ctlptr) is a NULL pointer or the len field of dataptr (ctlptr) is set to -1.

If a control part is specified, and flags is set to RS_HIPRI, a priority message is sent. If flags is set to 0, a non-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 no control part and no data part are specified, and flags is set to 0, no message is sent, and 0 is returned.

For non-priority messages, putmsg() will block if the stream write queue is full due to internal flow control conditions. For priority messages, putmsg() does not block on this condition. For non-priority messages, putmsg() does not block when the write queue is full and O_NDELAY is set. Instead, it fails and sets errno to EAGAIN.

putmsg() 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 has been specified. No partial message is sent.

RETURN VALUES

putmsg() returns:

0   on success.

-1  on failure and sets errno to indicate the error.

ERRORS

EAGAIN
    A non-priority message was specified, the O_NDELAY flag is set and the stream write queue is full due to internal flow control conditions.

    Buffers could not be allocated for the message that was to be created.

EBADF
    fd is not a valid file descriptor open for writing.

EFAULT
    ctlptr or dataptr points outside the allocated address space.

EINTR
    A signal was caught during the putmsg() system call.

EINVAL
    An undefined value was specified in flags.

    flags is set to RS_HIPRI and no control part was supplied.

    The stream referenced by fd is linked below a multiplexor.

ENOSTR
    A stream is not associated with fd.

ENXIO
    A hangup condition was generated downstream for the specified stream.

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.

    The control part of the message is larger than the maximum configured size of the control part of a message.

    The data part of the message is larger than the maximum configured size of the data part of a message.

A putmsg() also fails if a STREAMS error message had been processed by the stream head before the call to putmsg(). The error returned is the value contained in the STREAMS error message.

SEE ALSO
getmsg(2), intro(2), poll(2), read(2V), write(2V)