putmsg(2) putmsg(2)
NAME
putmsg - send a message on a stream
SYNOPSIS
#include <stropts.h>
int putmsg(int fd, const struct strbuf *ctlptr,
const struct strbuf *dataptr, int flags);
int putpmsg(int fd, const struct strbuf *ctlptr,
const struct strbuf *dataptr, int band, int flags);
DESCRIPTION
putmsg 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 function putpmsg 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.
fd specifies a file descriptor referencing an open stream. ctlptr
and dataptr each point to a strbuf structure, which contains the
following members:
int maxlen; /* not used */
int len; /* length of data */
void *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
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 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 is sent if either dataptr (ctlptr) is
NULL or the len field 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 (non-priority) message is
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putmsg(2) putmsg(2)
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. flags 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.
putmsg or putpmsg 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.
putmsg fails if one or more of the following are true:
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 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, or flags is
set to RS_HIPRI and no control part was supplied.
EINVAL The stream referenced by fd is linked below a
multiplexor.
EINVAL For putpmsg, if flags is set to MSG_HIPRI and band is
nonzero.
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putmsg(2) putmsg(2)
ENOSR Buffers could not be allocated for the message that was
to be created due to insufficient STREAMS memory
resources.
ENOSTR A stream is not associated with fd.
ENXIO A hangup condition was generated downstream for the
specified stream, or the other end of the pipe is
closed.
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.
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), putmsg(2), read(2), write(2).
Programmer's Guide: STREAMS.
DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Otherwise, a
value of -1 is returned and errno is set to indicate the error.
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