putmsg, putpmsg - send a message on a stream
struct strbuf *ctlptr,
struct strbuf *dataptr,
struct strbuf *ctlptr,
struct strbuf *dataptr,
The putmsg() function creates a message from a process 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 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 putpmsg() function does the same things as putmsg(), but the
process can send messages in different priority bands. Except where
noted, all requirements on putmsg() also pertain to putpmsg().
The fildes argument specifies a file descriptor referencing an open
stream. The ctlptr and dataptr arguments each point to a strbuf
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 indicates the number of bytes sent. The
maxlen member is not used by putmsg(). In a similar manner, the
argument 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 further below.
To send the data part of a message, dataptr must not be a null pointer
and the len member of dataptr must be 0 or greater. To send the
control part of a message, the corresponding values must be set for
ctlptr. No data (control) part will be sent if either dataptr
(ctlptr) is a null pointer or the len member of dataptr (ctlptr) is
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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 message (priority band
equal to 0) is sent. If a control part and data part are not
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
[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 set 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
The putmsg() function blocks 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
The putmsg() function also blocks, unless prevented by lack of
internal resources, while for the availability of message blocks in
the stream, regardless of priority of whether O_NONBLOCK has been
specified. No partial message is sent.
The putmsg() and putpmsg() functions are safe to be called by
multithreaded applications, and they are thread-safe for both POSIX
Threads and DCE User Threads. The putmsg() and putpmsg() functions
have cancellation points. They are async-signal safe and fork-safe.
They are not async-cancel safe.
Upon successful completion, putmsg() and putpmsg() return 0.
Otherwise, they return -1 and set errno to indicate the error.
[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, or buffers could not
be allocated for the message that was to be created.
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[EBADF] fildes is not a valid file descriptor open for writing.
[EINTR] A signal was caught during putmsg() or putpmsg().
[EINVAL] An undefined value is specified in flags, or flags is
set to RS_HIPRI or MSG_HIPRI and no control part is
supplied, or the stream or multiplexor referenced by
fildes is linked (directly or indirectly) downstream
from a multiplexor, or flags is set to MSG_HIPRI and
band is non-zero (for putpmsg() only).
[ENOSTR] A stream is not associated with fildes.
[ENXIO] A hangup condition was generated downstream for the
[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.
[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 STREAMS 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 the 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.
getmsg(2), poll(2), read(2), write(2), <stropts.h>, streamio(7).
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