PUTMSG(2) INTERACTIVE UNIX System PUTMSG(2)
NAME
putmsg - send a message on a stream
SYNOPSIS
#include <stropts.h>
int putmsg (fd, ctlptr, dataptr, flags)
int fd;
struct strbuf *ctlptr;
struct strbuf *dataptr;
int flags;
DESCRIPTION
The putmsg system call 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 which
contains the following members:
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 be non-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 (con-
trol) part will be sent if either dataptr (ctlptr) is NULL
or the len field of dataptr (ctlptr) is set to -1.
If a control part is specified, and flags is set to
RS_HIPRI, a priority 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.
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PUTMSG(2) INTERACTIVE UNIX System PUTMSG(2)
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 condi-
tion. 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.
The putmsg system call also blocks, unless prevented by lack
of internal resources, waiting for the availability of mes-
sage blocks in the stream, regardless of priority or whether
O_NDELAY has been specified. No partial message is sent.
The putmsg system call fails if one or more of the following
is true:
[EAGAIN] A non-priority message was specified, the
O_NDELAY flag is set, and the stream write
queue is full due to internal flow control con-
ditions.
[EAGAIN] 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 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
multiplexer.
[ENOSTR] A stream is not associated with fd.
[ENXIO] A hangup condition was generated downstream for
the specified stream.
[ERANGE] The size of the data part of the message does
not fall within the range specified by the max-
imum 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.
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PUTMSG(2) INTERACTIVE UNIX System PUTMSG(2)
A putmsg also fails if a STREAMS error message had been pro-
cessed by the stream head before the call to putmsg. The
error returned is the value contained in the STREAMS error
message.
SEE ALSO
intro(2), read(2), getmsg(2), poll(2), write(2).
STREAMS Primer.
STREAMS Programmer's Guide.
DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Oth-
erwise, a value of -1 is returned and errno is set to indi-
cate the error.
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