#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);
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().
fildes 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 here */ 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 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 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:
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.