streamio(7) UNIX System V streamio(7)
NAME
streamio - STREAMS ioctl commands
SYNOPSIS
#include <sys/types.h>
#include <stropts.h>
int ioctl (int fildes, int command, ... /* arg */);
DESCRIPTION
STREAMS [see intro(2)] ioctl commands are a subset of the ioctl(2) 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 performed 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 function, if
the stream referenced by fildes is linked below a multiplexor, or if
command is not a valid value for a stream.
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 system
calls to fail with errno set to this value.
COMMAND FUNCTIONS
The following ioctl commands, with error values indicated, are applicable
to all STREAMS files:
IPUSH Pushes the module whose name is pointed to by arg onto the
top of the current stream, just below the stream head. If
the stream is a pipe, the module will be inserted between
the stream heads of both ends of the pipe. It then calls
the open routine of the newly-pushed module. On failure,
errno is set to one of the following values:
EINVAL Invalid module name.
EFAULT arg points outside the allocated address space.
ENXIO Open routine of new module failed.
ENXIO Hangup received on fildes.
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streamio(7) UNIX System V streamio(7)
IPOP Removes the module just below the stream head of the stream
pointed to by fildes. To remove a module from a pipe
requires that the module was pushed on the side it is being
removed from. arg should be 0 in an IPOP request. On
failure, errno is set to one of the following values:
EINVAL No module present in the stream.
ENXIO Hangup received on fildes.
ILOOK Retrieves the name of the module just below the stream head
of the stream pointed to by fildes, and places it in a null
terminated character string pointed at by arg. The buffer
pointed to by arg should be at least FMNAMESZ+1 bytes long.
An (#include <sys/conf.h>) declaration is required. On
failure, errno is set to one of the following values:
EFAULT arg points outside the allocated address space.
EINVAL No module present in stream.
IFLUSH This request flushes all input and/or output queues,
depending on the value of arg. Legal arg values are:
FLUSHR Flush read queues.
FLUSHW Flush write queues.
FLUSHRW Flush read and write queues.
If a pipe or FIFO does not have any modules pushed, the read
queue of the stream head on either end is flushed depending
on the value of arg.
If FLUSHR is set and fildes is a pipe, the read queue for
that end of the pipe is flushed and the write queue for the
other end is flushed. If fildes is a FIFO, both queues are
flushed.
If FLUSHW is set and fildes is a pipe and the other end of
the pipe exists, the read queue for the other end of the
pipe is flushed and the write queue for this end is flushed.
If fildes is a FIFO, both queues of the FIFO are flushed.
If FLUSHRW is set, all read queues are flushed, that is, the
read queue for the FIFO and the read queue on both ends of
the pipe are flushed.
Correct flush handling of a pipe or FIFO with modules pushed
is achieved via the pipemod module. This module should be
the first module pushed onto a pipe so that it is at the
midpoint of the pipe itself.
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On failure, errno is set to one of the following values:
ENOSR Unable to allocate buffers for flush message
due to insufficient STREAMS memory resources.
EINVAL Invalid arg value.
ENXIO Hangup received on fildes.
IFLUSHBAND Flushes a particular band of messages. arg points to a
bandinfo structure that has the following members:
unsigned char bipri;
int biflag;
The biflag field may be one of FLUSHR, FLUSHW, or FLUSHRW
as described earlier.
ISETSIG Informs the stream head that the user wishes the kernel to
issue the SIGPOLL signal [see signal(2)] when a particular
event has occurred on the stream associated with fildes.
ISETSIG supports an asynchronous processing capability in
STREAMS. The value of arg is a bitmask that specifies the
events for which the user should be signaled. It is the
bitwise-OR of any combination of the following constants:
SINPUT Any message other than an MPCPROTO has arrived
on a stream head read queue. This event is
maintained for compatibility with prior UNIX
System V releases. This is set even if the
message is of zero length.
SRDNORM An ordinary (non-priority) message has arrived
on a stream head read queue. This is set even
if the message is of zero length.
SRDBAND A priority band message (band > 0) has arrived
on a stream head read queue. This is set even
if the message is of zero length.
SHIPRI A high priority message is present on the
stream head read queue. This is set even if
the message is of zero length.
SOUTPUT The write queue just below the stream head is
no longer full. This notifies the user that
there is room on the queue for sending (or
writing) data downstream.
SWRNORM This event is the same as SOUTPUT.
SWRBAND A priority band greater than 0 of a queue
downstream exists and is writable. This
notifies the user that there is room on the
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queue for sending (or writing) priority data
downstream.
SMSG A STREAMS signal message that contains the
SIGPOLL signal has reached the front of the
stream head read queue.
SERROR An MERROR message has reached the stream head.
SHANGUP An MHANGUP message has reached the stream
head.
SBANDURG When used in conjunction with SRDBAND, SIGURG
is generated instead of SIGPOLL when a priority
message reaches the front of the stream head
read queue.
A user process may choose to be signaled only of high
priority messages by setting the arg bitmask to the value
SHIPRI.
Processes that wish to receive SIGPOLL signals must
explicitly register to receive them using ISETSIG. If
several processes register to receive this signal for the
same event on the same stream, each process will be signaled
when the event occurs.
If the value of arg is zero, the calling process will be
unregistered and will not receive further SIGPOLL signals.
On failure, errno is set to one of the following values:
EINVAL arg value is invalid or arg is zero and process
is not registered to receive the SIGPOLL
signal.
EAGAIN Allocation of a data structure to store the
signal request failed.
IGETSIG Returns the events for which the calling process is
currently registered to be sent a SIGPOLL signal. The
events are returned as a bitmask pointed to by arg, where
the events are those specified in the description of
ISETSIG above. On failure, errno is set to one of the
following values:
EINVAL Process not registered to receive the SIGPOLL
signal.
EFAULT arg points outside the allocated address space.
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IFIND Compares the names of all modules currently present in the
stream to the name pointed to by arg, and returns 1 if the
named module is present in the stream. It returns 0 if the
named module is not present. On failure, errno is set to
one of the following values:
EFAULT arg points outside the allocated address space.
EINVAL arg does not contain a valid module name.
IPEEK Allows a user to retrieve the information in the first
message on the stream head read queue without taking the
message off the queue. IPEEK is analogous to getmsg(2)
except that it does not remove the message from the queue.
arg points to a strpeek structure which contains the
following members:
struct strbufctlbuf;
struct strbufdatabuf;
long flags;
The maxlen field in the ctlbuf and databuf strbuf structures
[see getmsg(2)] must be set to the number of bytes of
control information and/or data information, respectively,
to retrieve. flags may be set to RSHIPRI or 0. If
RSHIPRI is set, IPEEK will look for a high priority
message on the stream head read queue. Otherwise, IPEEK
will look for the first message on the stream head read
queue.
IPEEK returns 1 if a message was retrieved, and returns 0
if no message was found on the stream head read queue. It
does not wait for a message to arrive. On return, ctlbuf
specifies information in the control buffer, databuf
specifies information in the data buffer, and flags contains
the value RSHIPRI or 0. On failure, errno is set to the
following value:
EFAULT arg points, or the buffer area specified in
ctlbuf or databuf is, outside the allocated
address space.
EBADMSG Queued message to be read is not valid for
IPEEK
EINVAL Illegal value for flags.
ISRDOPT Sets the read mode [see read(2)] using the value of the
argument arg. Legal arg values are:
RNORM Byte-stream mode, the default.
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RMSGD Message-discard mode.
RMSGN Message-nondiscard mode.
In addition, treatment of control messages by the stream
head may be changed by setting the following flags in arg:
RPROTNORM Fail read() with EBADMSG if a control message
is at the front of the stream head read queue.
This is the default behavior.
RPROTDAT Deliver the control portion of a message as
data when a user issues read().
RPROTDIS Discard the control portion of a message,
delivering any data portion, when a user issues
a read().
On failure, errno is set to the following value:
EINVAL arg is not one of the above legal values.
IGRDOPT Returns the current read mode setting in an int pointed to
by the argument arg. Read modes are described in read(2).
On failure, errno is set to the following value:
EFAULT arg points outside the allocated address space.
INREAD Counts the number of data bytes in data blocks in the first
message on the stream head read queue, and places this value
in the location pointed to by arg. The return value for the
command is the number of messages on the stream head read
queue. For example, if zero is returned in arg, but the
ioctl return value is greater than zero, this indicates that
a zero-length message is next on the queue. On failure,
errno is set to the following value:
EFAULT arg points outside the allocated address space.
IFDINSERT 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 strbufctlbuf;
struct strbufdatabuf;
long flags;
int fildes;
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streamio(7) UNIX System V streamio(7)
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 IFDINSERT will store
a pointer. This pointer will be the address of the read
queue structure of the driver for the stream corresponding
to fildes in the strfdinsert structure. The len field in
the databuf strbuf structure must be set to the number of
bytes of data information to be sent with the message or
zero if no data part is to be sent.
flags specifies the type of message to be created. An
ordinary (non-priority) message is created if flags is set
to 0, a high priority message is created if flags is set to
RSHIPRI. For normal messages, IFDINSERT will block if the
stream write queue is full due to internal flow control
conditions. For high priority messages, IFDINSERT does not
block on this condition. For normal messages, IFDINSERT
does not block when the write queue is full and ONDELAY or
ONONBLOCK is set. Instead, it fails and sets errno to
EAGAIN.
IFDINSERT also blocks, unless prevented by lack of internal
resources, waiting for the availability of message blocks,
regardless of priority or whether ONDELAY or ONONBLOCK has
been specified. No partial message is sent. On failure,
errno is set to one of the following values:
EAGAIN A non-priority message was specified, the
ONDELAY or ONONBLOCK flag is set, and the
stream write queue is full due to internal flow
control conditions.
ENOSR Buffers could not be allocated for the message
that was to be created due to insufficient
STREAMS memory resources.
EFAULT arg points, or the buffer area specified in
ctlbuf or databuf is, outside the allocated
address space.
EINVAL One of the following: fildes in the
strfdinsert structure is not a valid, open
stream file descriptor; the size of a pointer
plus offset is greater than the len field for
the buffer specified through ctlptr; offset
does not specify a properly-aligned location in
the data buffer; an undefined value is stored
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in flags.
ENXIO Hangup received on fildes of the ioctl call or
fildes in the strfdinsert structure.
ERANGE The len field for the buffer specified through
databuf does not fall within the range
specified by the maximum and minimum packet
sizes of the topmost stream module, or the len
field for the buffer specified through databuf
is larger than the maximum configured size of
the data part of a message, or the len field
for the buffer specified through ctlbuf is
larger than the maximum configured size of the
control part of a message.
IFDINSERT can also fail if an error message was received by
the stream head of the stream corresponding to fildes in the
strfdinsert structure. In this case, errno will be set to
the value in the message.
ISTR Constructs an internal STREAMS ioctl message from the data
pointed to by arg, and sends that message downstream.
This mechanism is provided to send user ioctl requests to
downstream modules and drivers. It allows information to be
sent with the ioctl, and will return to the user any
information sent upstream by the downstream recipient.
ISTR blocks 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 fails with errno set to ETIME.
At most, one ISTR can be active on a stream. Further ISTR
calls will block until the active ISTR completes at the
stream head. The default timeout interval for these
requests is 15 seconds. The ONDELAY and ONONBLOCK [see
open(2)] flags have no effect on this call.
To send requests downstream, arg must point to a strioctl
structure which contains the following members:
int iccmd;
int ictimout;
int iclen;
char *icdp;
iccmd is the internal ioctl command intended for a
downstream module or driver and ictimout is the number of
seconds (-1 = infinite, 0 = use default, >0 = as specified)
an ISTR request will wait for acknowledgement before timing
out. The default timeout is infinite. iclen is the number
of bytes in the data argument and icdp is a pointer to the
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data argument. The iclen field 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 user (the buffer pointed to by icdp
should be large enough to contain the maximum amount of data
that any module or the driver in the stream can return).
The stream head will convert the information pointed to by
the strioctl structure to an internal ioctl command message
and send it downstream. On failure, errno is set to one of
the following values:
ENOSR Unable to allocate buffers for the ioctl
message due to insufficient STREAMS memory
resources.
EFAULT arg points, or the buffer area specified by
icdp and iclen (separately for data sent and
data returned) is, outside the allocated
address space.
EINVAL iclen is less than 0 or iclen is larger than
the maximum configured size of the data part of
a message or ictimout is less than -1.
ENXIO Hangup received on fildes.
ETIME A downstream ioctl timed out before
acknowledgement was received.
An ISTR 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 ioctl command sent downstream fails. For these
cases, ISTR will fail with errno set to the value in the
message.
ISWROPT Sets the write mode using the value of the argument arg.
Legal bit settings for arg are:
SNDZERO Send a zero-length message downstream when a
write of 0 bytes occurs.
To not send a zero-length message when a write of 0 bytes
occurs, this bit must not be set in arg.
On failure, errno may be set to the following value:
EINVAL arg is the the above legal value.
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IGWROPT Returns the current write mode setting, as described above,
in the int that is pointed to by the argument arg.
ISENDFD Requests the stream associated with fildes to send a
message, containing a file pointer, to the stream head at
the other end of a stream pipe. The file pointer
corresponds to arg, which must be an open file descriptor.
ISENDFD converts arg into the corresponding system file
pointer. It allocates a message block and inserts the file
pointer in the block. The user id and group id associated
with the sending process are also inserted. This message is
placed directly on the read queue [see intro(2)] of the
stream head at the other end of the stream pipe to which it
is connected. On failure, errno is set to one of the
following values:
EAGAIN The sending stream is unable to allocate a
message block to contain the file pointer.
EAGAIN The read queue of the receiving stream head is
full and cannot accept the message sent by
ISENDFD.
EBADF arg is not a valid, open file descriptor.
EINVAL fildes is not connected to a stream pipe.
ENXIO Hangup received on fildes.
IRECVFD Retrieves the file descriptor associated with the message
sent by an ISENDFD ioctl over a stream pipe. arg is a
pointer to a data buffer large enough to hold an strrecvfd
data structure containing the following members:
int fd;
uidt uid;
gidt gid;
char fill[8];
fd is an integer file descriptor. uid and gid are the user
id and group id, respectively, of the sending stream.
If ONDELAY and ONONBLOCK are clear [see open(2)], IRECVFD
will block until a message is present at the stream head.
If ONDELAY or ONONBLOCK is set, IRECVFD will fail with
errno set to EAGAIN if no message is present at the stream
head.
If the message at the stream head is a message sent by an
ISENDFD, a new user file descriptor is allocated for the
file pointer contained in the message. The new file
descriptor is placed in the fd field of the strrecvfd
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streamio(7) UNIX System V streamio(7)
structure. The structure is copied into the user data
buffer pointed to by arg. On failure, errno is set to one
of the following values:
EAGAIN A message is not present at the stream head
read queue, and the ONDELAY or ONONBLOCK flag
is set.
EBADMSG The message at the stream head read queue is
not a message containing a passed file
descriptor.
EFAULT arg points outside the allocated address space.
EMFILE NOFILES file descriptors are currently open.
ENXIO Hangup received on fildes.
EOVERFLOW uid or gid is too large to be stored in the
structure pointed to by arg.
ILIST Allows the user to list all the module names on the stream,
up to and including the topmost driver name. If arg is
NULL, the return value is the number of modules, including
the driver, that are on the stream pointed to by fildes.
This allows the user to allocate enough space for the module
names. If arg is non-NULL, it should point to an strlist
structure that has the following members:
int slnmods;
struct strmlist *slmodlist;
The strmlist structure has the following member:
char lname[FMNAMESZ+1];
slnmods indicates the number of entries the user has
allocated in the array and on return, slmodlist contains
the list of module names. The return value indicates the
number of entries that have been filled in. On failure,
errno may be set to one of the following values:
EINVAL The slnmods member is less than 1.
EAGAIN Unable to allocate buffers
IATMARK 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 may be
multiple marked messages on the stream head read queue. It
may take the following values:
ANYMARK Check if the message is marked.
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LASTMARK Check if the message is the last one marked on
the queue.
The return value is 1 if the mark condition is satisfied and
0 otherwise. On failure, errno may be set to the following
value:
EINVAL Invalid arg value.
ICKBAND 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. On failure, errno may be set to the following
value:
EINVAL Invalid arg value.
IGETBAND Returns the priority band of the first message on the stream
head read queue in the integer referenced by arg. On
failure, errno may be set to the following value:
ENODATA No message on the stream head read queue.
ICANPUT Check 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. On failure, errno may be set to
the following value:
EINVAL Invalid arg value.
ISETCLTIME Allows the user to set the time the stream head will delay
when a stream is closing and there are data on the write
queues. Before closing each module and driver, the stream
head will delay for the specified amount of time to allow
the data to drain. If, after the delay, data are still
present, data will be flushed. arg is a pointer to the
number of milliseconds to delay, rounded up to the nearest
legal value on the system. The default is fifteen seconds.
On failure, errno may be set to the following value:
EINVAL Invalid arg value.
IGETCLTIME Returns the close time delay in the long pointed by arg.
The following four commands are used for connecting and disconnecting
multiplexed STREAMS configurations.
ILINK Connects two streams, where fildes is the file descriptor of
the stream connected to the multiplexing driver, and arg is
the file descriptor of the stream connected to another
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driver. The stream designated by arg gets connected below
the multiplexing driver. ILINK requires the multiplexing
driver to send an acknowledgement message to the stream head
regarding the linking operation. This call returns a
multiplexor ID number (an identifier used to disconnect the
multiplexor, see IUNLINK) on success, and a -1 on failure.
On failure, errno is set to one of the following values:
ENXIO Hangup received on fildes.
ETIME Time out before acknowledgement message was
received at stream head.
EAGAIN Temporarily unable to allocate storage to
perform the ILINK.
ENOSR Unable to allocate storage to perform the
ILINK due to insufficient STREAMS memory
resources.
EBADF arg is not a valid, open file descriptor.
EINVAL fildes stream does not support multiplexing.
EINVAL arg is not a stream, or is already linked under
a multiplexor.
EINVAL The specified link operation would cause a
"cycle" in the resulting configuration; that
is, if a given driver is linked into a
multiplexing configuration in more than one
place.
EINVAL fildes is the file descriptor of a pipe or
FIFO.
An ILINK can also fail while waiting for the multiplexing
driver to acknowledge the link request, if a message
indicating an error or a hangup is received at the stream
head of fildes. In addition, an error code can be returned
in the positive or negative acknowledgement message. For
these cases, ILINK will fail with errno set to the value in
the message.
IUNLINK Disconnects the two streams specified by fildes and arg.
fildes is the file descriptor of the stream connected to the
multiplexing driver. arg is the multiplexor ID number that
was returned by the ILINK. If arg is -1, then all Streams
which were linked to fildes are disconnected. As in ILINK,
this command requires the multiplexing driver to acknowledge
the unlink. On failure, errno is set to one of the
following values:
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ENXIO Hangup received on fildes.
ETIME Time out before acknowledgement message was
received at stream head.
ENOSR Unable to allocate storage to perform the
IUNLINK due to insufficient STREAMS memory
resources.
EINVAL arg is an invalid multiplexor ID number or
fildes is not the stream on which the ILINK
that returned arg was performed.
EINVAL fildes is the file descriptor of a pipe or
FIFO.
An IUNLINK can also fail while waiting for the multiplexing
driver to acknowledge the link request, if a message
indicating an error or a hangup is received at the stream
head of fildes. In addition, an error code can be returned
in the positive or negative acknowledgement message. For
these cases, IUNLINK will fail with errno set to the value
in the message.
IPLINK Connects two streams, where fildes is the file descriptor of
the stream connected to the multiplexing driver, and arg is
the file descriptor of the stream connected to another
driver. The stream designated by arg gets connected via a
persistent link below the multiplexing driver. IPLINK
requires the multiplexing driver to send an acknowledgement
message to the stream head regarding the linking operation.
This call creates a persistent link which can exist even if
the file descriptor fildes associated with the upper stream
to the multiplexing driver is closed. This call returns a
multiplexor ID number (an identifier that may be used to
disconnect the multiplexor, see IPUNLINK) on success, and a
-1 on failure. On failure, errno may be set to one of the
following values:
ENXIO Hangup received on fildes.
ETIME Time out before acknowledgement message was
received at the stream head.
EAGAIN Unable to allocate STREAMS storage to perform
the IPLINK.
EBADF arg is not a valid, open file descriptor.
EINVAL fildes does not support multiplexing.
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EINVAL arg is not a stream or is already linked under
a multiplexor.
EINVAL The specified link operation would cause a
"cycle" in the resulting configuration; that
is, if a given stream head is linked into a
multiplexing configuration in more than one
place.
EINVAL fildes is the file descriptor of a pipe or
FIFO.
An IPLINK can also fail while waiting for the multiplexing
driver to acknowledge the link request, if a message
indicating an error on a hangup is received at the stream
head of fildes. In addition, an error code can be returned
in the positive or negative acknowledgement message. For
these cases, IPLINK will fail with errno set to the value
in the message.
IPUNLINK Disconnects the two streams specified by fildes and arg that
are connected with a persistent link. fildes is the file
descriptor of the stream connected to the multiplexing
driver. arg is the multiplexor ID number that was returned
by IPLINK when a stream was linked below the multiplexing
driver. If arg is MUXIDALL then all streams which are
persistent links to fildes are disconnected. As in IPLINK,
this command requires the multiplexing driver to acknowledge
the unlink. On failure, errno may be set to one of the
following values:
ENXIO Hangup received on fildes.
ETIME Time out before acknowledgement message was
received at the stream head.
EAGAIN Unable to allocate buffers for the
acknowledgement message.
EINVAL Invalid multiplexor ID number.
EINVAL fildes is the file descriptor of a pipe or
FIFO.
An IPUNLINK can also fail while waiting for the
multiplexing driver to acknowledge the link request if a
message indicating an error or a hangup is received at the
stream head of fildes. In addition, an error code can be
returned in the positive or negative acknowledgement
message. For these cases, IPUNLINK will fail with errno
set to the value in the message.
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SEE ALSO
close(2), fcntl(2), getmsg(2), intro(2), ioctl(2), open(2), poll(2),
putmsg(2), read(2), signal(2), write(2), signal(5).
Programmer's Guide: STREAMS.
DIAGNOSTICS
Unless specified otherwise above, the return value from ioctl is 0 upon
success and -1 upon failure with errno set as indicated.
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