#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 putpmsg() function is equivalent to putmsg(), except that 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 structure.
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 to be 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, the application shall ensure that dataptr is not a null pointer and the len member of dataptr is 0 or greater. To send the control part of a message, the application shall ensure that the corresponding values are set for ctlptr. No data (control) part shall be sent if either dataptr(ctlptr) is a null pointer or the len member 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 shall be sent. If no control part is specified, and flags is set to RS_HIPRI, putmsg() shall fail and set errno to [EINVAL]. If flags is set to 0, a normal message (priority band equal to 0) shall be sent. If a control part and data part are not specified and flags is set to 0, no message shall be sent and 0 shall be returned.
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()
shall fail and set
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 shall be 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()
shall fail and set
errno
to
[EINVAL].
If
flags
is set to MSG_BAND, then a message shall be 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 shall be sent and 0 shall be returned.
The putmsg() function shall block if the STREAM write queue is full due to internal flow control conditions, with the following exceptions:
The putmsg() function shall also block, unless prevented by lack of internal resources, while waiting for the availability of message blocks in the STREAM, regardless of priority or whether O_NONBLOCK has been specified. No partial message shall be sent.
In addition,
putmsg()
and
putpmsg()
shall 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.
The following sections are informative.
The value of fd is assumed to refer to an open STREAMS file. This call to putmsg() does the following:
#include <stropts.h> #include <string.h> ... int fd; char *ctrlbuf = "This is the control part"; char *databuf = "This is the data part"; struct strbuf ctrl; struct strbuf data; int ret; ctrl.buf = ctrlbuf; ctrl.len = strlen(ctrlbuf); data.buf = databuf; data.len = strlen(databuf); ret = putmsg(fd, &ctrl, &data, MSG_HIPRI);
This example has the same effect as the previous example. In this example, however, the putpmsg() function creates and sends the message to the STREAMS file.
#include <stropts.h> #include <string.h> ... int fd; char *ctrlbuf = "This is the control part"; char *databuf = "This is the data part"; struct strbuf ctrl; struct strbuf data; int ret; ctrl.buf = ctrlbuf; ctrl.len = strlen(ctrlbuf); data.buf = databuf; data.len = strlen(databuf); ret = putpmsg(fd, &ctrl, &data, 0, MSG_HIPRI);
The Base Definitions volume of POSIX.1-2017, <stropts.h>
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .