PUTMSG(2) System Calls Manual PUTMSG(2)
putmsg - send a message on a stream
int putmsg(fd, ctlptr, dataptr, flags)
struct strbuf *ctlptr;
struct strbuf *dataptr;
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
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
If a control part is specified, and flags is set to RS_HIPRI, a prior-
ity 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, regard-
less of priority or whether O_NDELAY has been specified. No partial
message is sent.
0 on success.
-1 on failure and sets errno to indicate the error.
EAGAIN A non-priority message was specified, the O_NDELAY flag
is set and the stream write queue is full due to inter-
nal 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
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 sup-
The stream referenced by fd is linked below a multi-
ENOSTR A stream is not associated with fd.
ENXIO A hangup condition was generated downstream for the
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 maxi-
mum 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.
getmsg(2), intro(2), poll(2), read(2V), write(2V)
21 January 1990 PUTMSG(2)