.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "IOCTL" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" ioctl 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
ioctl \- control a STREAMS device (\fBSTREAMS\fP)
.SH SYNOPSIS
.LP
\fB#include <stropts.h>
.br
.sp
int ioctl(int\fP \fIfildes\fP\fB, int\fP \fIrequest\fP\fB, ... /*
arg */); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIioctl\fP() function shall perform a variety of control functions
on STREAMS devices. For non-STREAMS devices, the
functions performed by this call are unspecified. The \fIrequest\fP
argument and an optional third argument (with varying type)
shall be passed to and interpreted by the appropriate part of the
STREAM associated with \fIfildes\fP.
.LP
The \fIfildes\fP argument is an open file descriptor that refers to
a device.
.LP
The \fIrequest\fP argument selects the control function to be performed
and shall depend on the STREAMS device being
addressed.
.LP
The \fIarg\fP argument represents additional information that is needed
by this specific STREAMS device to perform the
requested function. The type of \fIarg\fP depends upon the particular
control request, but it shall be either an integer or a
pointer to a device-specific data structure.
.LP
The \fIioctl\fP() commands applicable to STREAMS, their arguments,
and error conditions that apply to each individual command
are described below.
.LP
The following \fIioctl\fP() commands, with error values indicated,
are applicable to all STREAMS files:
.TP 7
I_PUSH
Pushes the module whose name is pointed to by \fIarg\fP onto the top
of the current STREAM, just below the STREAM head. It
then calls the \fIopen\fP() function of the newly-pushed module. 
.LP
The \fIioctl\fP() function with the I_PUSH command shall fail if:
.TP 7
.B EINVAL
.RS
Invalid module name.
.RE
.TP 7
.B ENXIO
.RS
Open function of new module failed.
.RE
.TP 7
.B ENXIO
.RS
Hangup received on \fIfildes\fP.
.RE
.sp
.TP 7
I_POP
Removes the module just below the STREAM head of the STREAM pointed
to by \fIfildes\fP. The \fIarg\fP argument should be 0 in
an I_POP request. 
.LP
The \fIioctl\fP() function with the I_POP command shall fail if:
.TP 7
.B EINVAL
.RS
No module present in the STREAM.
.RE
.TP 7
.B ENXIO
.RS
Hangup received on \fIfildes\fP.
.RE
.sp
.TP 7
I_LOOK
Retrieves the name of the module just below the STREAM head of the
STREAM pointed to by \fIfildes\fP, and places it in a
character string pointed to by \fIarg\fP. The buffer pointed to by
\fIarg\fP should be at least FMNAMESZ+1 bytes long, where
FMNAMESZ is defined in \fI<stropts.h>\fP. 
.LP
The \fIioctl\fP() function with the I_LOOK command shall fail if:
.TP 7
.B EINVAL
.RS
No module present in the STREAM.
.RE
.sp
.TP 7
I_FLUSH
Flushes read and/or write queues, depending on the value of \fIarg\fP.
Valid \fIarg\fP values are: 
.TP 7
FLUSHR
.RS
Flush all read queues.
.RE
.TP 7
FLUSHW
.RS
Flush all write queues.
.RE
.TP 7
FLUSHRW
.RS
Flush all read and all write queues.
.RE
.sp
.LP
The \fIioctl\fP() function with the I_FLUSH command shall fail if:
.TP 7
.B EINVAL
.RS
Invalid \fIarg\fP value.
.RE
.TP 7
.B EAGAIN \fRor\fP ENOSR
.RS
.sp
Unable to allocate buffers for flush message.
.RE
.TP 7
.B ENXIO
.RS
Hangup received on \fIfildes\fP.
.RE
.sp
.TP 7
I_FLUSHBAND
Flushes a particular band of messages. The \fIarg\fP argument points
to a \fBbandinfo\fP structure. The \fIbi_flag\fP member
may be one of FLUSHR, FLUSHW, or FLUSHRW as described above. The \fIbi_pri\fP
member determines the priority band to be
flushed.
.TP 7
I_SETSIG
Requests that the STREAMS implementation send the SIGPOLL signal to
the calling process when a particular event has occurred on
the STREAM associated with \fIfildes\fP. I_SETSIG supports an asynchronous
processing capability in STREAMS. The value of
\fIarg\fP is a bitmask that specifies the events for which the process
should be signaled. It is the bitwise-inclusive OR of any
combination of the following constants: 
.TP 7
S_RDNORM
.RS
A normal (priority band set to 0) message has arrived at the head
of a STREAM head read queue. A signal shall be generated even
if the message is of zero length.
.RE
.TP 7
S_RDBAND
.RS
A message with a non-zero priority band has arrived at the head of
a STREAM head read queue. A signal shall be generated even
if the message is of zero length.
.RE
.TP 7
S_INPUT
.RS
A message, other than a high-priority message, has arrived at the
head of a STREAM head read queue. A signal shall be generated
even if the message is of zero length.
.RE
.TP 7
S_HIPRI
.RS
A high-priority message is present on a STREAM head read queue. A
signal shall be generated even if the message is of zero
length.
.RE
.TP 7
S_OUTPUT
.RS
The write queue for normal data (priority band 0) just below the STREAM
head is no longer full. This notifies the process that
there is room on the queue for sending (or writing) normal data downstream.
.RE
.TP 7
S_WRNORM
.RS
Equivalent to S_OUTPUT.
.RE
.TP 7
S_WRBAND
.RS
The write queue for a non-zero priority band just below the STREAM
head is no longer full. This notifies the process that there
is room on the queue for sending (or writing) priority data downstream.
.RE
.TP 7
S_MSG
.RS
A STREAMS signal message that contains the SIGPOLL signal has reached
the front of the STREAM head read queue.
.RE
.TP 7
S_ERROR
.RS
Notification of an error condition has reached the STREAM head.
.RE
.TP 7
S_HANGUP
.RS
Notification of a hangup has reached the STREAM head.
.RE
.TP 7
S_BANDURG
.RS
When used in conjunction with S_RDBAND, SIGURG is generated instead
of SIGPOLL when a priority message reaches the front of the
STREAM head read queue.
.RE
.sp
.LP
If \fIarg\fP is 0, the calling process shall be unregistered and shall
not receive further SIGPOLL signals for the stream
associated with \fIfildes\fP.
.LP
Processes that wish to receive SIGPOLL signals shall ensure that they
explicitly register to receive them using I_SETSIG. If
several processes register to receive this signal for the same event
on the same STREAM, each process shall be signaled when the
event occurs.
.LP
The \fIioctl\fP() function with the I_SETSIG command shall fail if:
.TP 7
.B EINVAL
.RS
The value of \fIarg\fP is invalid.
.RE
.TP 7
.B EINVAL
.RS
The value of \fIarg\fP is 0 and the calling process is not registered
to receive the SIGPOLL signal.
.RE
.TP 7
.B EAGAIN
.RS
There were insufficient resources to store the signal request.
.RE
.sp
.TP 7
I_GETSIG
Returns the events for which the calling process is currently registered
to be sent a SIGPOLL signal. The events are returned
as a bitmask in an \fBint\fP pointed to by \fIarg\fP, where the events
are those specified in the description of I_SETSIG above. 
.LP
The \fIioctl\fP() function with the I_GETSIG command shall fail if:
.TP 7
.B EINVAL
.RS
Process is not registered to receive the SIGPOLL signal.
.RE
.sp
.TP 7
I_FIND
Compares the names of all modules currently present in the STREAM
to the name pointed to by \fIarg\fP, and returns 1 if the
named module is present in the STREAM, or returns 0 if the named module
is not present. 
.LP
The \fIioctl\fP() function with the I_FIND command shall fail if:
.TP 7
.B EINVAL
.RS
\fIarg\fP does not contain a valid module name.
.RE
.sp
.TP 7
I_PEEK
Retrieves the information in the first message on the STREAM head
read queue without taking the message off the queue. It is
analogous to \fIgetmsg\fP() except that this command does not remove
the message from the
queue. The \fIarg\fP argument points to a \fBstrpeek\fP structure.
.LP
The application shall ensure that the \fImaxlen\fP member in the \fBctlbuf\fP
and \fBdatabuf strbuf\fP structures is set to
the number of bytes of control information and/or data information,
respectively, to retrieve. The \fIflags\fP member may be
marked RS_HIPRI or 0, as described by \fIgetmsg\fP(). If the process
sets \fIflags\fP to
RS_HIPRI, for example, I_PEEK shall only look for a high-priority
message on the STREAM head read queue.
.LP
I_PEEK returns 1 if a message was retrieved, and returns 0 if no message
was found on the STREAM head read queue, or if the
RS_HIPRI flag was set in \fIflags\fP and a high-priority message was
not present on the STREAM head read queue. It does not wait
for a message to arrive. On return, \fBctlbuf\fP specifies information
in the control buffer, \fBdatabuf\fP specifies information
in the data buffer, and \fIflags\fP contains the value RS_HIPRI or
0.
.TP 7
I_SRDOPT
Sets the read mode using the value of the argument \fIarg\fP. Read
modes are described in \fIread\fP(). Valid \fIarg\fP flags are: 
.TP 7
RNORM
.RS
Byte-stream mode, the default.
.RE
.TP 7
RMSGD
.RS
Message-discard mode.
.RE
.TP 7
RMSGN
.RS
Message-nondiscard mode.
.RE
.sp
.LP
The bitwise-inclusive OR of RMSGD and RMSGN shall return [EINVAL].
The bitwise-inclusive OR of RNORM and either RMSGD or RMSGN
shall result in the other flag overriding RNORM which is the default.
.LP
In addition, treatment of control messages by the STREAM head may
be changed by setting any of the following flags in
\fIarg\fP:
.TP 7
RPROTNORM
.RS
Fail \fIread\fP() with [EBADMSG] if a message containing a control
part is at the front
of the STREAM head read queue.
.RE
.TP 7
RPROTDAT
.RS
Deliver the control part of a message as data when a process issues
a \fIread\fP().
.RE
.TP 7
RPROTDIS
.RS
Discard the control part of a message, delivering any data portion,
when a process issues a \fIread\fP().
.RE
.sp
.LP
The \fIioctl\fP() function with the I_SRDOPT command shall fail if:
.TP 7
.B EINVAL
.RS
The \fIarg\fP argument is not valid.
.RE
.sp
.TP 7
I_GRDOPT
Returns the current read mode setting, as described above, in an \fBint\fP
pointed to by the argument \fIarg\fP. Read modes
are described in \fIread\fP().
.TP 7
I_NREAD
Counts the number of data bytes in the data part of the first message
on the STREAM head read queue and places this value in
the \fBint\fP pointed to by \fIarg\fP. The return value for the command
shall be the number of messages on the STREAM head read
queue. For example, if 0 is returned in \fIarg\fP, but the \fIioctl\fP()
return value is greater than 0, this indicates that a
zero-length message is next on the queue.
.TP 7
I_FDINSERT
Creates a message from 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. The \fIarg\fP argument points
to a \fBstrfdinsert\fP structure. 
.LP
The application shall ensure that the \fIlen\fP member in the \fBctlbuf
strbuf\fP structure is set to the size of a
\fBt_uscalar_t\fP plus the number of bytes of control information
to be sent with the message. The \fIfildes\fP member specifies
the file descriptor of the other STREAM, and the \fIoffset\fP member,
which must be suitably aligned for use as a
\fBt_uscalar_t\fP, specifies the offset from the start of the control
buffer where I_FDINSERT shall store a \fBt_uscalar_t\fP
whose interpretation is specific to the STREAM end. The application
shall ensure that the \fIlen\fP member in the \fBdatabuf
strbuf\fP structure is set to the number of bytes of data information
to be sent with the message, or to 0 if no data part is to
be sent.
.LP
The \fIflags\fP member specifies the type of message to be created.
A normal message is created if \fIflags\fP is set to 0,
and a high-priority message is created if \fIflags\fP is set to RS_HIPRI.
For non-priority messages, I_FDINSERT shall block if the
STREAM write queue is full due to internal flow control conditions.
For priority messages, I_FDINSERT does not block on this
condition. For non-priority messages, I_FDINSERT does not block when
the write queue is full and O_NONBLOCK is set. Instead, it
fails and sets \fIerrno\fP to [EAGAIN].
.LP
I_FDINSERT 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_NONBLOCK has been specified.
No partial message is sent.
.LP
The \fIioctl\fP() function with the I_FDINSERT command shall fail
if:
.TP 7
.B EAGAIN
.RS
A non-priority message is specified, the O_NONBLOCK flag is set, and
the STREAM write queue is full due to internal flow
control conditions.
.RE
.TP 7
.B EAGAIN \fRor\fP ENOSR
.RS
.sp
Buffers cannot be allocated for the message that is to be created.
.RE
.TP 7
.B EINVAL
.RS
One of the following: 
.RS
.IP " *" 3
The \fIfildes\fP member of the \fBstrfdinsert\fP structure is not
a valid, open STREAM file descriptor.
.LP
.IP " *" 3
The size of a \fBt_uscalar_t\fP plus \fIoffset\fP is greater than
the \fIlen\fP member for the buffer specified through
\fBctlbuf\fP.
.LP
.IP " *" 3
The \fIoffset\fP member does not specify a properly-aligned location
in the data buffer.
.LP
.IP " *" 3
An undefined value is stored in \fIflags\fP.
.LP
.RE
.RE
.TP 7
.B ENXIO
.RS
Hangup received on the STREAM identified by either the \fIfildes\fP
argument or the \fIfildes\fP member of the
\fBstrfdinsert\fP structure.
.RE
.TP 7
.B ERANGE
.RS
The \fIlen\fP member for the buffer specified through \fBdatabuf\fP
does not fall within the range specified by the maximum
and minimum packet sizes of the topmost STREAM module; or the \fIlen\fP
member for the buffer specified through \fBdatabuf\fP is
larger than the maximum configured size of the data part of a message;
or the \fIlen\fP member for the buffer specified through
\fBctlbuf\fP is larger than the maximum configured size of the control
part of a message.
.RE
.sp
.TP 7
I_STR
Constructs an internal STREAMS \fIioctl\fP() message from the data
pointed to by \fIarg\fP, and sends that message
downstream. 
.LP
This mechanism is provided to send \fIioctl\fP() requests to downstream
modules and drivers. It allows information to be sent
with \fIioctl\fP(), and returns to the process any information sent
upstream by the downstream recipient. I_STR shall block until
the system responds with either a positive or negative acknowledgement
message, or until the request times out after some period of
time. If the request times out, it shall fail with \fIerrno\fP set
to [ETIME].
.LP
At most, one I_STR can be active on a STREAM. Further I_STR calls
shall block until the active I_STR completes at the STREAM
head. The default timeout interval for these requests is 15 seconds.
The O_NONBLOCK flag has no effect on this call.
.LP
To send requests downstream, the application shall ensure that \fIarg\fP
points to a \fBstrioctl\fP structure.
.LP
The \fIic_cmd\fP member is the internal \fIioctl\fP() command intended
for a downstream module or driver and \fIic_timout\fP
is the number of seconds (-1=infinite, 0=use implementation-defined
timeout interval, >0=as specified) an I_STR request shall
wait for acknowledgement before timing out. \fIic_len\fP is the number
of bytes in the data argument, and \fIic_dp\fP is a
pointer to the data argument. The \fIic_len\fP member has two uses:
on input, it contains the length of the data argument passed
in, and on return from the command, it contains the number of bytes
being returned to the process (the buffer pointed to by
\fIic_dp\fP should be large enough to contain the maximum amount of
data that any module or the driver in the STREAM can
return).
.LP
The STREAM head shall convert the information pointed to by the \fBstrioctl\fP
structure to an internal \fIioctl\fP() command
message and send it downstream.
.LP
The \fIioctl\fP() function with the I_STR command shall fail if:
.TP 7
.B EAGAIN \fRor\fP ENOSR
.RS
.sp
Unable to allocate buffers for the \fIioctl\fP() message.
.RE
.TP 7
.B EINVAL
.RS
The \fIic_len\fP member is less than 0 or larger than the maximum
configured size of the data part of a message, or
\fIic_timout\fP is less than -1.
.RE
.TP 7
.B ENXIO
.RS
Hangup received on \fIfildes\fP.
.RE
.TP 7
.B ETIME
.RS
A downstream \fIioctl\fP() timed out before acknowledgement was received.
.RE
.sp
.LP
An I_STR can also fail while waiting for an acknowledgement if a message
indicating an error or a hangup is received at the
STREAM head. In addition, an error code can be returned in the positive
or negative acknowledgement message, in the event the
\fIioctl\fP() command sent downstream fails. For these cases, I_STR
shall fail with \fIerrno\fP set to the value in the
message.
.TP 7
I_SWROPT
Sets the write mode using the value of the argument \fIarg\fP. Valid
bit settings for \fIarg\fP are: 
.TP 7
SNDZERO
.RS
Send a zero-length message downstream when a \fIwrite\fP() of 0 bytes
occurs. To not
send a zero-length message when a \fIwrite\fP() of 0 bytes occurs,
the application shall
ensure that this bit is not set in \fIarg\fP (for example, \fIarg\fP
would be set to 0).
.RE
.sp
.LP
The \fIioctl\fP() function with the I_SWROPT command shall fail if:
.TP 7
.B EINVAL
.RS
\fIarg\fP is not the above value.
.RE
.sp
.TP 7
I_GWROPT
Returns the current write mode setting, as described above, in the
\fBint\fP that is pointed to by the argument
\fIarg\fP.
.TP 7
I_SENDFD
Creates a new reference to the open file description associated with
the file descriptor \fIarg\fP, and writes a message on
the STREAMS-based pipe \fIfildes\fP containing this reference, together
with the user ID and group ID of the calling process. 
.LP
The \fIioctl\fP() function with the I_SENDFD command shall fail if:
.TP 7
.B EAGAIN
.RS
The sending STREAM is unable to allocate a message block to contain
the file pointer; or the read queue of the receiving STREAM
head is full and cannot accept the message sent by I_SENDFD.
.RE
.TP 7
.B EBADF
.RS
The \fIarg\fP argument is not a valid, open file descriptor.
.RE
.TP 7
.B EINVAL
.RS
The \fIfildes\fP argument is not connected to a STREAM pipe.
.RE
.TP 7
.B ENXIO
.RS
Hangup received on \fIfildes\fP.
.RE
.sp
.TP 7
I_RECVFD
Retrieves the reference to an open file description from a message
written to a STREAMS-based pipe using the I_SENDFD command,
and allocates a new file descriptor in the calling process that refers
to this open file description. The \fIarg\fP argument is a
pointer to a \fBstrrecvfd\fP data structure as defined in \fI<stropts.h>\fP.
.LP
The \fIfd\fP member is a file descriptor. The \fIuid\fP and \fIgid\fP
members are the effective user ID and effective group
ID, respectively, of the sending process.
.LP
If O_NONBLOCK is not set, I_RECVFD shall block until a message is
present at the STREAM head. If O_NONBLOCK is set, I_RECVFD
shall fail with \fIerrno\fP set to [EAGAIN] if no message is present
at the STREAM head.
.LP
If the message at the STREAM head is a message sent by an I_SENDFD,
a new file descriptor shall be allocated for the open file
descriptor referenced in the message. The new file descriptor is placed
in the \fIfd\fP member of the \fBstrrecvfd\fP structure
pointed to by \fIarg\fP.
.LP
The \fIioctl\fP() function with the I_RECVFD command shall fail if:
.TP 7
.B EAGAIN
.RS
A message is not present at the STREAM head read queue and the O_NONBLOCK
flag is set.
.RE
.TP 7
.B EBADMSG
.RS
The message at the STREAM head read queue is not a message containing
a passed file descriptor.
.RE
.TP 7
.B EMFILE
.RS
The process has the maximum number of file descriptors currently open
that it is allowed.
.RE
.TP 7
.B ENXIO
.RS
Hangup received on \fIfildes\fP.
.RE
.sp
.TP 7
I_LIST
Allows the process to list all the module names on the STREAM, up
to and including the topmost driver name. If \fIarg\fP is a
null pointer, the return value shall be the number of modules, including
the driver, that are on the STREAM pointed to by
\fIfildes\fP. This lets the process allocate enough space for the
module names. Otherwise, it should point to a \fBstr_list\fP
structure. 
.LP
The \fIsl_nmods\fP member indicates the number of entries the process
has allocated in the array. Upon return, the
\fIsl_modlist\fP member of the \fBstr_list\fP structure shall contain
the list of module names, and the number of entries that
have been filled into the \fIsl_modlist\fP array is found in the \fIsl_nmods\fP
member (the number includes the number of modules
including the driver). The return value from \fIioctl\fP() shall be
0. The entries are filled in starting at the top of the STREAM
and continuing downstream until either the end of the STREAM is reached,
or the number of requested modules ( \fIsl_nmods\fP) is
satisfied.
.LP
The \fIioctl\fP() function with the I_LIST command shall fail if:
.TP 7
.B EINVAL
.RS
The \fIsl_nmods\fP member is less than 1.
.RE
.TP 7
.B EAGAIN \fRor\fP ENOSR
.RS
.sp
Unable to allocate buffers.
.RE
.sp
.TP 7
I_ATMARK
Allows the process to see if the message at the head of the STREAM
head read queue is marked by some module downstream. The
\fIarg\fP argument determines how the checking is done when there
may be multiple marked messages on the STREAM head read queue.
It may take on the following values: 
.TP 7
ANYMARK
.RS
Check if the message is marked.
.RE
.TP 7
LASTMARK
.RS
Check if the message is the last one marked on the queue.
.RE
.sp
.LP
The bitwise-inclusive OR of the flags ANYMARK and LASTMARK is permitted.
.LP
The return value shall be 1 if the mark condition is satisfied; otherwise,
the value shall be 0.
.LP
The \fIioctl\fP() function with the I_ATMARK command shall fail if:
.TP 7
.B EINVAL
.RS
Invalid \fIarg\fP value.
.RE
.sp
.TP 7
I_CKBAND
Checks if the message of a given priority band exists on the STREAM
head read queue. This shall return 1 if a message of the
given priority exists, 0 if no such message exists, or -1 on error.
\fIarg\fP should be of type \fBint\fP. 
.LP
The \fIioctl\fP() function with the I_CKBAND command shall fail if:
.TP 7
.B EINVAL
.RS
Invalid \fIarg\fP value.
.RE
.sp
.TP 7
I_GETBAND
Returns the priority band of the first message on the STREAM head
read queue in the integer referenced by \fIarg\fP. 
.LP
The \fIioctl\fP() function with the I_GETBAND command shall fail if:
.TP 7
.B ENODATA
.RS
No message on the STREAM head read queue.
.RE
.sp
.TP 7
I_CANPUT
Checks if a certain band is writable. \fIarg\fP is set to the priority
band in question. The return value shall be 0 if the
band is flow-controlled, 1 if the band is writable, or -1 on error.
.LP
The \fIioctl\fP() function with the I_CANPUT command shall fail if:
.TP 7
.B EINVAL
.RS
Invalid \fIarg\fP value.
.RE
.sp
.TP 7
I_SETCLTIME
This request allows the process to set the time the STREAM head shall
delay when a STREAM is closing and there is data on the
write queues. Before closing each module or driver, if there is data
on its write queue, the STREAM head shall delay for the
specified amount of time to allow the data to drain. If, after the
delay, data is still present, it shall be flushed. The
\fIarg\fP argument is a pointer to an integer specifying the number
of milliseconds to delay, rounded up to the nearest valid
value. If I_SETCLTIME is not performed on a STREAM, an implementation-defined
default timeout interval is used. 
.LP
The \fIioctl\fP() function with the I_SETCLTIME command shall fail
if:
.TP 7
.B EINVAL
.RS
Invalid \fIarg\fP value.
.RE
.sp
.TP 7
I_GETCLTIME
Returns the close time delay in the integer pointed to by \fIarg\fP.
.sp
.SS Multiplexed STREAMS Configurations
.LP
The following commands are used for connecting and disconnecting multiplexed
STREAMS configurations. These commands use an
implementation-defined default timeout interval.
.TP 7
I_LINK
Connects two STREAMs, where \fIfildes\fP is the file descriptor of
the STREAM connected to the multiplexing driver, and
\fIarg\fP is the file descriptor of the STREAM connected to another
driver. The STREAM designated by \fIarg\fP is connected below
the multiplexing driver. I_LINK requires the multiplexing driver to
send an acknowledgement message to the STREAM head regarding
the connection. This call shall return a multiplexer ID number (an
identifier used to disconnect the multiplexer; see I_UNLINK) on
success, and -1 on failure. 
.LP
The \fIioctl\fP() function with the I_LINK command shall fail if:
.TP 7
.B ENXIO
.RS
Hangup received on \fIfildes\fP.
.RE
.TP 7
.B ETIME
.RS
Timeout before acknowledgement message was received at STREAM head.
.RE
.TP 7
.B EAGAIN \fRor\fP ENOSR
.RS
.sp
Unable to allocate STREAMS storage to perform the I_LINK.
.RE
.TP 7
.B EBADF
.RS
The \fIarg\fP argument is not a valid, open file descriptor.
.RE
.TP 7
.B EINVAL
.RS
The \fIfildes\fP argument does not support multiplexing; or \fIarg\fP
is not a STREAM or is already connected downstream from
a multiplexer; or the specified I_LINK operation would connect the
STREAM head in more than one place in the multiplexed
STREAM.
.RE
.sp
.LP
An I_LINK can also fail while waiting for the multiplexing driver
to acknowledge the request, if a message indicating an error
or a hangup is received at the STREAM head of \fIfildes\fP. In addition,
an error code can be returned in the positive or negative
acknowledgement message. For these cases, I_LINK fails with \fIerrno\fP
set to the value in the message.
.TP 7
I_UNLINK
Disconnects the two STREAMs specified by \fIfildes\fP and \fIarg\fP.
\fIfildes\fP is the file descriptor of the STREAM
connected to the multiplexing driver. The \fIarg\fP argument is the
multiplexer ID number that was returned by the I_LINK
\fIioctl\fP() command when a STREAM was connected downstream from
the multiplexing driver. If \fIarg\fP is MUXID_ALL, then all
STREAMs that were connected to \fIfildes\fP shall be disconnected.
As in I_LINK, this command requires acknowledgement. 
.LP
The \fIioctl\fP() function with the I_UNLINK command shall fail if:
.TP 7
.B ENXIO
.RS
Hangup received on \fIfildes\fP.
.RE
.TP 7
.B ETIME
.RS
Timeout before acknowledgement message was received at STREAM head.
.RE
.TP 7
.B EAGAIN \fRor\fP ENOSR
.RS
.sp
Unable to allocate buffers for the acknowledgement message.
.RE
.TP 7
.B EINVAL
.RS
Invalid multiplexer ID number.
.RE
.sp
.LP
An I_UNLINK can also fail while waiting for the multiplexing driver
to acknowledge the request if a message indicating an error
or a hangup is received at the STREAM head of \fIfildes\fP. In addition,
an error code can be returned in the positive or negative
acknowledgement message. For these cases, I_UNLINK shall fail with
\fIerrno\fP set to the value in the message.
.TP 7
I_PLINK
Creates a \fIpersistent connection\fP between two STREAMs, where \fIfildes\fP
is the file descriptor of the STREAM connected
to the multiplexing driver, and \fIarg\fP is the file descriptor of
the STREAM connected to another driver. This call shall create
a persistent connection which can exist even if the file descriptor
\fIfildes\fP associated with the upper STREAM to the
multiplexing driver is closed. The STREAM designated by \fIarg\fP
gets connected via a persistent connection below the
multiplexing driver. I_PLINK requires the multiplexing driver to send
an acknowledgement message to the STREAM head. This call
shall return a multiplexer ID number (an identifier that may be used
to disconnect the multiplexer; see I_PUNLINK) on success, and
-1 on failure. 
.LP
The \fIioctl\fP() function with the I_PLINK command shall fail if:
.TP 7
.B ENXIO
.RS
Hangup received on \fIfildes\fP.
.RE
.TP 7
.B ETIME
.RS
Timeout before acknowledgement message was received at STREAM head.
.RE
.TP 7
.B EAGAIN \fRor\fP ENOSR
.RS
.sp
Unable to allocate STREAMS storage to perform the I_PLINK.
.RE
.TP 7
.B EBADF
.RS
The \fIarg\fP argument is not a valid, open file descriptor.
.RE
.TP 7
.B EINVAL
.RS
The \fIfildes\fP argument does not support multiplexing; or \fIarg\fP
is not a STREAM or is already connected downstream from
a multiplexer; or the specified I_PLINK operation would connect the
STREAM head in more than one place in the multiplexed
STREAM.
.RE
.sp
.LP
An I_PLINK can also fail while waiting for the multiplexing driver
to acknowledge the request, if a message indicating an error
or a hangup is received at the STREAM head of \fIfildes\fP. In addition,
an error code can be returned in the positive or negative
acknowledgement message. For these cases, I_PLINK shall fail with
\fIerrno\fP set to the value in the message.
.TP 7
I_PUNLINK
Disconnects the two STREAMs specified by \fIfildes\fP and \fIarg\fP
from a persistent connection. The \fIfildes\fP argument
is the file descriptor of the STREAM connected to the multiplexing
driver. The \fIarg\fP argument is the multiplexer ID number
that was returned by the I_PLINK \fIioctl\fP() command when a STREAM
was connected downstream from the multiplexing driver. If
\fIarg\fP is MUXID_ALL, then all STREAMs which are persistent connections
to \fIfildes\fP shall be disconnected. As in I_PLINK,
this command requires the multiplexing driver to acknowledge the request.
.LP
The \fIioctl\fP() function with the I_PUNLINK command shall fail if:
.TP 7
.B ENXIO
.RS
Hangup received on \fIfildes\fP.
.RE
.TP 7
.B ETIME
.RS
Timeout before acknowledgement message was received at STREAM head.
.RE
.TP 7
.B EAGAIN \fRor\fP ENOSR
.RS
.sp
Unable to allocate buffers for the acknowledgement message.
.RE
.TP 7
.B EINVAL
.RS
Invalid multiplexer ID number.
.RE
.sp
.LP
An I_PUNLINK can also fail while waiting for the multiplexing driver
to acknowledge the request if a message indicating an error
or a hangup is received at the STREAM head of \fIfildes\fP. In addition,
an error code can be returned in the positive or negative
acknowledgement message. For these cases, I_PUNLINK shall fail with
\fIerrno\fP set to the value in the message.
.sp
.SH RETURN VALUE
.LP
Upon successful completion, \fIioctl\fP() shall return a value other
than -1 that depends upon the STREAMS device control
function. Otherwise, it shall return -1 and set \fIerrno\fP to indicate
the error.
.SH ERRORS
.LP
Under the following general conditions, \fIioctl\fP() shall fail if:
.TP 7
.B EBADF
The \fIfildes\fP argument is not a valid open file descriptor.
.TP 7
.B EINTR
A signal was caught during the \fIioctl\fP() operation.
.TP 7
.B EINVAL
The STREAM or multiplexer referenced by \fIfildes\fP is linked (directly
or indirectly) downstream from a multiplexer.
.sp
.LP
If an underlying device driver detects an error, then \fIioctl\fP()
shall fail if:
.TP 7
.B EINVAL
The \fIrequest\fP or \fIarg\fP argument is not valid for this device.
.TP 7
.B EIO
Some physical I/O error has occurred.
.TP 7
.B ENOTTY
The \fIfildes\fP argument is not associated with a STREAMS device
that accepts control functions.
.TP 7
.B ENXIO
The \fIrequest\fP and \fIarg\fP arguments are valid for this device
driver, but the service requested cannot be performed on
this particular sub-device.
.TP 7
.B ENODEV
The \fIfildes\fP argument refers to a valid STREAMS device, but the
corresponding device driver does not support the
\fIioctl\fP() function.
.sp
.LP
If a STREAM is connected downstream from a multiplexer, any \fIioctl\fP()
command except I_UNLINK and I_PUNLINK shall set
\fIerrno\fP to [EINVAL].
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
The implementation-defined timeout interval for STREAMS has historically
been 15 seconds.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fISTREAMS\fP, \fIclose\fP(), \fIfcntl\fP(), \fIgetmsg\fP(), \fIopen\fP(),
\fIpipe\fP(), \fIpoll\fP(), \fIputmsg\fP(), \fIread\fP(), \fIsigaction\fP(),
\fIwrite\fP(), the
Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<stropts.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .