putmsg - send a message on a stream
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);
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
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
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 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:
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_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
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
EIO fildes is open to a device that is in the process of
closing, or the other end of the pipe is closed.
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
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.
getmsg(2), intro(2), poll(2), putmsg(2), read(2), write(2)
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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