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putmsg(2)
putmsg(2) System Calls putmsg(2)
NAME
putmsg, putpmsg - send a message on a stream
SYNOPSIS
#include <stropts.h>
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);
DESCRIPTION
The putmsg() function creates a message from user-specified buffer(s)
and sends the message to a STREAMS file. The message may contain either
a data part or a control part, or even both. The data and control parts
to be sent are distinguished by placement in separate buffers, as de‐
scribed 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. Ex‐
cept where noted, all information pertaining 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 struc‐
ture, 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 str‐
buf structure points to the buffer where the control information re‐
sides, and the len member indicates 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 mes‐
sage. The flags argument indicates what type of message should be sent
and is described later.
To send the data part of a message, dataptr is not NULL, and the len
member of dataptr has a value of 0 or greater. To send the control part
of a message, the corresponding values are set for ctlptr. No data
(control) 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 speci‐
fied, 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. 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 EIN‐
VAL. 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.
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 specified. No partial message is sent.
RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, −1 is returned
and errno is set to indicate the error.
ERRORS
The putmsg() and putpmsg() functions will fail if:
EADI The user-specified buffer for the data part of a mes‐
sage is enabled for ADI, and an ADI version mismatch is
detected while the system reads data from the buffer.
For more information, see the adi(3C) man page.
EAGAIN A non-priority message is 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.
EFAULT The ctlptr or dataptr argument points to an illegal ad‐
dress.
EINTR A signal is caught during the execution of the putmsg()
function.
EINVAL An undefined value is 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 multi‐
plexor.
ENOSR Buffers are not allocated for the message that are not
to be created due to insufficient streams memory re‐
sources.
ENOSTR The fildes argument is not associated with a stream.
ENXIO A hangup condition is generated downstream for the
specified stream, or the other end of the pipe is
closed.
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 thread. This error condi‐
tion occurs only with SUS-conforming applications. See
standards(7).
ERANGE The size of the data part of the message is not 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() fail if the stream head has
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:
EINVAL The flags argument is set to MSG_HIPRI and band is non-zero.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ StandardSee stan‐
dards(7).
SEE ALSO
getmsg(2), Intro(2), poll(2), read(2), write(2), attributes(7), stan‐
dards(7)
STREAMS Programming Guide
HISTORY
The putmsg() function has been included in all Sun and Oracle releases
of Solaris.
The putpmsg() function has been included in Solaris since the Solaris
2.0 release.
Oracle Solaris 11.4 30 Jan 2023 putmsg(2)