putmsg(2) putmsg(2)
NAME
putmsg, putpmsg - 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
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putmsg(2) putmsg(2)
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 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_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_NONBLOCK has been specified. No partial message is sent.
Return Values
On success, putmsg returns 0. On failure, putmsg returns -1
and sets errno to identify the error.
Errors
In the following conditions, putmsg fails and sets errno to:
Copyright 1994 Novell, Inc. Page 2
putmsg(2) putmsg(2)
EACCES fildes is open to a dynamic device, and write
permission on the device is denied.
EAGAIN A non-priority message was specified, the
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.
EIO fildes is open to a device that is in the process
of closing.
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.
EIO 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
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putmsg(2) putmsg(2)
larger than the maximum configured size of the
data part of a message.
ENODEV fildes points to a device that does not support
the putmsg(2) operation.
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.
REFERENCES
getmsg(2), intro(2), poll(2), putmsg(2), read(2), write(2)
NOTICES
Considerations for Threads Programming
Open file descriptors are a process resource and available to
any sibling thread; if used concurrently, actions by one
thread can interfere with those of a sibling.
While one thread is blocked, siblings might still be
executing.
Copyright 1994 Novell, Inc. Page 4