putmsg(2)

DESCRIPTION

The putmsg() function creates a message from a process 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 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 things as putmsg(), but the process can send messages in different priority bands. Except where noted, all requirements on putmsg() also pertain to putpmsg().

The fildes argument specifies a file descriptor referencing an open stream. The ctlptr and dataptr arguments each point to a strbuf structure.

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 sent. The maxlen member is not used by putmsg(). In a similar manner, the argument 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 further below.

To send the data part of a message, dataptr must not be a null pointer and the len member of dataptr must be 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 member of dataptr (ctlptr) is set to -1.

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 message (priority band equal to 0) is sent. If a control part and data part are not 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 set 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.

The putmsg() function blocks 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_NONBLOCK is set.

The putmsg() function also blocks, unless prevented by lack of internal resources, while for the availability of message blocks in the stream, regardless of priority of whether O_NONBLOCK has been specified. No partial message is sent.

MULTITHREAD USAGE

The putmsg() and putpmsg() functions are safe to be called by multithreaded applications, and they are thread-safe for both POSIX Threads and DCE User Threads. The putmsg() and putpmsg() functions have cancellation points. They are async-signal safe and fork-safe. They are not async-cancel safe.

RETURN VALUE

Upon successful completion, putmsg() and putpmsg() return 0. Otherwise, they return -1 and set errno to indicate the error.

ERRORS

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.

SEE ALSO

getmsg(2), poll(2), read(2), write(2), <stropts.h>, streamio(7).