HP-UX Reference (11i v2 07/12) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

s
streamio(7) streamio(7)
NAME
streamio - STREAMS ioctl commands
SYNOPSIS
#include <sys/types.h>
#include <stropts.h>
int ioctl(int
fildes, int command,
... /* arg */);
DESCRIPTION
STREAMS ioctl commands are a subset of the
ioctl() system calls which perform a variety of control
functions on streams.
fildes is an open file descriptor that refers to a stream. command determines the control function to be per-
formed as described below. arg represents additional information that is needed by this command. The
type of arg depends upon the command, but it is generally an integer or a pointer to a command-specific
data structure. The command and arg are interpreted by the stream head. Certain combinations of these
arguments may be passed to a module or driver in the stream.
Since these STREAMS commands are a subset of
ioctl, they are subject to the errors described there. In
addition to those errors, the call will fail with errno set to [EINVAL], without processing a control func-
tion, if the stream referenced by fildes is linked below a multiplexor, or if command is not a valid value for
astream.
Also, as described in
ioctl, STREAMS modules and drivers can detect errors. In this case, the module or
driver sends an error message to the stream head containing an error value. This causes subsequent sys-
tem calls to fail with errno set to this value.
The following ioctl commands, with error values indicated, are applicable to all STREAMS files:
I_ATMARK Allows the user to see if the current message on the stream head read queue is
"marked" by some module downstream. arg determines how the checking is done
when there are multiple marked messages on the stream head read queue. It may
take the following values:
ANYMARK Checks if the message is marked.
LASTMARK Checks if the message is the last one that is marked on the queue.
If both ANYMARK and LASTMARK are set, ANYMARK supersedes LASTMARK.
The return value is 1 if the mark condition is satisfied and 0 otherwise.
I_CANPUT Checks if a certain band is writable. arg is set to the priority band in question. The
return value is 0 if the priority band arg is flow controlled, 1 if the band is writable, or
-1 on error.
I_CKBAND Check if the message of a given priority band exists on the stream head read queue.
This returns 1 if a message of a given priority exists, or -1 on error. arg should be an
integer containing the value of the priority band in question.
I_FDINSERT Creates a message from user specified buffer(s), adds information about another
stream and sends the message downstream. The message contains a control part and
an optional data part. The data and control parts to be sent are distinguished by
placement in separate buffers, as described below.
arg points to a
strfdinsert structure which contains the following members:
struct strbuf ctlbuf;
struct strbuf databuf;
long options;
int fildes;
int offset;
The len field in the ctlbuf strbuf structure (see putmsg(2)) must be set to the
size of a pointer plus the number of bytes of control information to be sent with the
message. fildes in the strfdinsert structure specifies the file descriptor of the
other stream. offset, which must be word-aligned, specifies the number of bytes
beyond the beginning of the control buffer where I_FDINSERT will store a pointer.
This pointer will be the address of the read queue structure of the driver for the
HP-UX 11i Version 2: December 2007 Update − 1 − Hewlett-Packard Company 171