putmsg, putpmsg - send a message on a stream
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);
The putmsg() function creates a message from user-specified
buffer(s) and sends the message to a STREAMS file. The mes-
sage may contain either a data part, a control part, or
both. The data and control parts to be sent are dis-
tinguished 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 pertain-
ing 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 indi-
cates 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 (con-
trol) 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 mes-
sage 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 condi-
tion. 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 speci-
fied. No partial message is sent.
Upon successful completion, 0 is returned. Otherwise, -1 is
returned and errno is set to indicate the error.
The putmsg() and putpmsg() functions will fail if:
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.
The ctlptr or dataptr argument points to an illegal
EINTR A signal was caught during the execution of the
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 mul-
ENOSR Buffers could not be allocated for the message that
was to be created due to insufficient STREAMS memory
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
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 process. This error con-
dition occurs only with SUS-compliant applications.
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:
The flags argument is set to MSG_HIPRI and band is
intro(2), getmsg(2), poll(2), read(2), write(2), stan-
STREAMS Programming Guide
Man(1) output converted with