IOCTL
Section: POSIX Programmer's Manual (3P)
Updated: 2017
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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.
NAME
ioctl
--- control a STREAMS device (
STREAMS)
SYNOPSIS
#include <stropts.h>
int ioctl(int fildes, int request, ... /* arg */);
DESCRIPTION
The
ioctl()
function shall perform a variety of control functions on STREAMS
devices. For non-STREAMS devices, the functions performed by this call
are unspecified. The
request
argument and an optional third argument (with varying type) shall be
passed to and interpreted by the appropriate part of the STREAM
associated with
fildes.
The
fildes
argument is an open file descriptor that refers to a device.
The
request
argument selects the control function to be performed and shall
depend on the STREAMS device being addressed.
The
arg
argument represents additional information that is needed by this
specific STREAMS device to perform the requested function. The type of
arg
depends upon the particular control request, but it shall be either an
integer or a pointer to a device-specific data structure.
The
ioctl()
commands applicable to STREAMS, their arguments, and error conditions
that apply to each individual command are described below.
The following
ioctl()
commands, with error values indicated, are applicable to all STREAMS
files:
- I_PUSH
-
Pushes the module whose name is pointed to by
arg
onto the top of the current STREAM, just below the STREAM head. It then
calls the
open()
function of the newly-pushed module.
-
The
ioctl()
function with the I_PUSH command shall fail if:
- EINVAL
-
Invalid module name.
- ENXIO
-
Open function of new module failed.
- ENXIO
-
Hangup received on
fildes.
- I_POP
-
Removes the module just below the STREAM head of the STREAM pointed to
by
fildes.
The
arg
argument should be 0 in an I_POP request.
-
The
ioctl()
function with the I_POP command shall fail if:
- EINVAL
-
No module present in the STREAM.
- ENXIO
-
Hangup received on
fildes.
- I_LOOK
-
Retrieves the name of the module just below the STREAM head of the
STREAM pointed to by
fildes,
and places it in a character string pointed to by
arg.
The buffer pointed to by
arg
should be at least FMNAMESZ+1
bytes long, where FMNAMESZ is defined in
<stropts.h>.
-
The
ioctl()
function with the I_LOOK command shall fail if:
- EINVAL
-
No module present in the STREAM.
- I_FLUSH
-
Flushes read and/or write queues, depending on the value of
arg.
Valid
arg
values are:
-
- FLUSHR
-
Flush all read queues.
- FLUSHW
-
Flush all write queues.
- FLUSHRW
-
Flush all read and all write queues.
The
ioctl()
function with the I_FLUSH command shall fail if:
- EINVAL
-
Invalid
arg
value.
- EAGAIN or ENOSR
-
Unable to allocate buffers for flush message.
- ENXIO
-
Hangup received on
fildes.
- I_FLUSHBAND
-
Flushes a particular band of messages. The
arg
argument points to a
bandinfo
structure. The
bi_flag
member may be one of FLUSHR, FLUSHW, or FLUSHRW as described above. The
bi_pri
member determines the priority band to be flushed.
- 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
fildes.
I_SETSIG supports an asynchronous processing capability in STREAMS. The
value of
arg
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:
-
- S_RDNORM
-
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.
- S_RDBAND
-
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.
- S_INPUT
-
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.
- S_HIPRI
-
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.
- S_OUTPUT
-
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.
- S_WRNORM
-
Equivalent to S_OUTPUT.
- S_WRBAND
-
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.
- S_MSG
-
A STREAMS signal message that contains the SIGPOLL signal has reached
the front of the STREAM head read queue.
- S_ERROR
-
Notification of an error condition has reached the STREAM head.
- S_HANGUP
-
Notification of a hangup has reached the STREAM head.
- S_BANDURG
-
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.
If
arg
is 0, the calling process shall be unregistered and shall not receive
further SIGPOLL signals for the stream associated with
fildes.
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.
The
ioctl()
function with the I_SETSIG command shall fail if:
- EINVAL
-
The value of
arg
is invalid.
- EINVAL
-
The value of
arg
is 0 and the calling process is not registered to receive
the SIGPOLL signal.
- EAGAIN
-
There were insufficient resources to store the signal request.
- 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
int
pointed to by
arg,
where the events are those specified in the description of
I_SETSIG above.
-
The
ioctl()
function with the I_GETSIG command shall fail if:
- EINVAL
-
Process is not registered to receive the SIGPOLL signal.
- I_FIND
-
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, or returns
0 if the named module is not present.
-
The
ioctl()
function with the I_FIND command shall fail if:
- EINVAL
-
arg
does not contain a valid module name.
- 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
getmsg()
except that this command does not remove the message from the queue.
The
arg
argument points to a
strpeek
structure.
-
The application shall ensure that the
maxlen
member in the
ctlbuf
and
databuf strbuf
structures is set to the number of bytes of control information and/or
data information, respectively, to retrieve. The
flags
member may be marked RS_HIPRI or 0, as described by
getmsg().
If the process sets
flags
to RS_HIPRI, for example, I_PEEK shall only look for a high-priority
message on the STREAM head read queue.
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
flags
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,
ctlbuf
specifies information in the control buffer,
databuf
specifies information in the data buffer, and
flags
contains the value RS_HIPRI or 0.
- I_SRDOPT
-
Sets the read mode using the value of the argument
arg.
Read modes are described in
read().
Valid
arg
flags are:
-
- RNORM
-
Byte-stream mode, the default.
- RMSGD
-
Message-discard mode.
- RMSGN
-
Message-nondiscard mode.
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.
In addition, treatment of control messages by the STREAM head may be
changed by setting any of the following flags in
arg:
- RPROTNORM
-
Fail
read()
with
[EBADMSG]
if a message containing a control part is at the front of the
STREAM head read queue.
- RPROTDAT
-
Deliver the control part of a message as data when a process issues a
read().
- RPROTDIS
-
Discard the control part of a message, delivering any data portion,
when a process issues a
read().
The
ioctl()
function with the I_SRDOPT command shall fail if:
- EINVAL
-
The
arg
argument is not valid.
- I_GRDOPT
-
Returns the current read mode setting, as described above, in an
int
pointed to by the argument
arg.
Read modes are described in
read().
- 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
int
pointed to by
arg.
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
arg,
but the
ioctl()
return value is greater than 0, this indicates that a zero-length
message is next on the queue.
- 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
arg
argument points to a
strfdinsert
structure.
-
The application shall ensure that the
len
member in the
ctlbuf strbuf
structure is set to the size of a
t_uscalar_t
plus the number of bytes of control information to be sent with the
message. The
fildes
member specifies the file descriptor of the other STREAM, and the
offset
member, which must be suitably aligned for use as a
t_uscalar_t,
specifies the offset from the start of the control buffer where
I_FDINSERT shall store a
t_uscalar_t
whose interpretation is specific to the STREAM end. The application
shall ensure that the
len
member in the
databuf strbuf
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.
The
flags
member specifies the type of message to be created. A normal message is
created if
flags
is set to 0, and a high-priority message is created if
flags
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
errno
to
[EAGAIN].
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.
The
ioctl()
function with the I_FDINSERT command shall fail if:
- EAGAIN
-
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.
- EAGAIN or ENOSR
-
Buffers cannot be allocated for the message that is to be created.
- EINVAL
-
One of the following:
-
- --
-
The
fildes
member of the
strfdinsert
structure is not a valid, open STREAM file descriptor.
- --
-
The size of a
t_uscalar_t
plus
offset
is greater than the
len
member for the buffer specified through
ctlbuf.
- --
-
The
offset
member does not specify a properly-aligned location in the data buffer.
- --
-
An undefined value is stored in
flags.
- ENXIO
-
Hangup received on the STREAM identified by either the
fildes
argument or the
fildes
member of the
strfdinsert
structure.
- ERANGE
-
The
len
member 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
member for the buffer specified through
databuf
is larger than the maximum configured size of the data part of a
message; or the
len
member for the buffer specified through
ctlbuf
is larger than the maximum configured size of the control part of a
message.
- I_STR
-
Constructs an internal STREAMS
ioctl()
message from the data pointed to by
arg,
and sends that message downstream.
-
This mechanism is provided to send
ioctl()
requests to downstream modules and drivers. It allows information to be
sent with
ioctl(),
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
errno
set to
[ETIME].
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.
To send requests downstream, the application shall ensure that
arg
points to a
strioctl
structure.
The
ic_cmd
member is the internal
ioctl()
command intended for a downstream module or driver and
ic_timout
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.
ic_len
is the number of bytes in the data argument, and
ic_dp
is a pointer to the data argument. The
ic_len
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
ic_dp
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 shall convert the information pointed to by the
strioctl
structure to an internal
ioctl()
command message and send it downstream.
The
ioctl()
function with the I_STR command shall fail if:
- EAGAIN or ENOSR
-
Unable to allocate buffers for the
ioctl()
message.
- EINVAL
-
The
ic_len
member is less than 0 or larger than the maximum configured size of the
data part of a message, or
ic_timout
is less than -1.
- ENXIO
-
Hangup received on
fildes.
- ETIME
-
A downstream
ioctl()
timed out before acknowledgement was received.
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
ioctl()
command sent downstream fails. For these cases, I_STR shall fail with
errno
set to the value in the message.
- I_SWROPT
-
Sets the write mode using the value of the argument
arg.
Valid 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, the application shall ensure that this bit is not
set in
arg
(for example,
arg
would be set to 0).
The
ioctl()
function with the I_SWROPT command shall fail if:
- EINVAL
-
arg
is not the above value.
- I_GWROPT
-
Returns the current write mode setting, as described above, in the
int
that is pointed to by the argument
arg.
- I_SENDFD
-
Creates a new reference to the open file description associated with
the file descriptor
arg,
and writes a message on the STREAMS-based pipe
fildes
containing this reference, together with the user ID and group ID of
the calling process.
-
The
ioctl()
function with the I_SENDFD command shall fail if:
- EAGAIN
-
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.
- EBADF
-
The
arg
argument is not a valid, open file descriptor.
- EINVAL
-
The
fildes
argument is not connected to a STREAM pipe.
- ENXIO
-
Hangup received on
fildes.
The
ioctl()
function with the I_SENDFD command may fail if:
- EINVAL
-
The
arg
argument is equal to the
fildes
argument.
- 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
arg
argument is a pointer to a
strrecvfd
data structure as defined in
<stropts.h>.
-
The
fd
member is a file descriptor. The
uid
and
gid
members are the effective user ID and effective group ID, respectively,
of the sending process.
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
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 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
fd
member of the
strrecvfd
structure pointed to by
arg.
The
ioctl()
function with the I_RECVFD command shall fail if:
- EAGAIN
-
A message is not present at the STREAM head read queue and the
O_NONBLOCK flag is set.
- EBADMSG
-
The message at the STREAM head read queue is not a message containing a
passed file descriptor.
- EMFILE
-
All file descriptors available to the process are currently open.
- ENXIO
-
Hangup received on
fildes.
- I_LIST
-
Allows the process to list all the module names on the STREAM, up to
and including the topmost driver name. If
arg
is a null pointer, the return value shall be the number of modules,
including the driver, that are on the STREAM pointed to by
fildes.
This lets the process allocate enough space for the module names.
Otherwise, it should point to a
str_list
structure.
-
The
sl_nmods
member indicates the number of entries the process has allocated in the
array. Upon return, the
sl_modlist
member of the
str_list
structure shall contain the list of module names, and the number of
entries that have been filled into the
sl_modlist
array is found in the
sl_nmods
member (the number includes the number of modules including the
driver). The return value from
ioctl()
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 (sl_nmods)
is satisfied.
The
ioctl()
function with the I_LIST command shall fail if:
- EINVAL
-
The
sl_nmods
member is less than 1.
- EAGAIN or ENOSR
-
Unable to allocate buffers.
- 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
arg
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:
-
- ANYMARK
-
Check if the message is marked.
- LASTMARK
-
Check if the message is the last one marked on the queue.
The bitwise-inclusive OR of the flags ANYMARK and LASTMARK is permitted.
The return value shall be 1 if the mark condition is satisfied;
otherwise, the value shall be 0.
The
ioctl()
function with the I_ATMARK command shall fail if:
- EINVAL
-
Invalid
arg
value.
- 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.
arg
should be of type
int.
-
The
ioctl()
function with the I_CKBAND command shall fail if:
- EINVAL
-
Invalid
arg
value.
- I_GETBAND
-
Returns the priority band of the first message on the STREAM head read
queue in the integer referenced by
arg.
-
The
ioctl()
function with the I_GETBAND command shall fail if:
- ENODATA
-
No message on the STREAM head read queue.
- I_CANPUT
-
Checks if a certain band is writable.
arg
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.
-
The
ioctl()
function with the I_CANPUT command shall fail if:
- EINVAL
-
Invalid
arg
value.
- 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
arg
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.
-
The
ioctl()
function with the I_SETCLTIME command shall fail if:
- EINVAL
-
Invalid
arg
value.
- I_GETCLTIME
-
Returns the close time delay in the integer pointed to by
arg.
Multiplexed STREAMS Configurations
The following commands are used for connecting and disconnecting
multiplexed STREAMS configurations. These commands use an
implementation-defined default timeout interval.
- I_LINK
-
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
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.
-
The
ioctl()
function with the I_LINK command shall fail if:
- ENXIO
-
Hangup received on
fildes.
- ETIME
-
Timeout before acknowledgement message was received at STREAM head.
- EAGAIN or ENOSR
-
Unable to allocate STREAMS storage to perform the I_LINK.
- EBADF
-
The
arg
argument is not a valid, open file descriptor.
- EINVAL
-
The
fildes
argument does not support multiplexing; or
arg
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.
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
fildes.
In addition, an error code can be returned in the positive or negative
acknowledgement message. For these cases, I_LINK fails with
errno
set to the value in the message.
- I_UNLINK
-
Disconnects the two STREAMs specified by
fildes
and
arg.
fildes
is the file descriptor of the STREAM connected to the multiplexing
driver. The
arg
argument is the multiplexer ID number that was returned by the I_LINK
ioctl()
command when a STREAM was connected downstream from the multiplexing
driver. If
arg
is MUXID_ALL, then all STREAMs that were connected to
fildes
shall be disconnected. As in I_LINK, this command requires
acknowledgement.
-
The
ioctl()
function with the I_UNLINK command shall fail if:
- ENXIO
-
Hangup received on
fildes.
- ETIME
-
Timeout before acknowledgement message was received at STREAM head.
- EAGAIN or ENOSR
-
Unable to allocate buffers for the acknowledgement message.
- EINVAL
-
Invalid multiplexer ID number.
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
fildes.
In addition, an error code can be returned in the positive or negative
acknowledgement message. For these cases, I_UNLINK shall fail with
errno
set to the value in the message.
- I_PLINK
-
Creates a
persistent connection
between 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. This
call shall create a persistent connection which can exist even if the
file descriptor
fildes
associated with the upper STREAM to the multiplexing driver is closed.
The STREAM designated by
arg
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.
-
The
ioctl()
function with the I_PLINK command shall fail if:
- ENXIO
-
Hangup received on
fildes.
- ETIME
-
Timeout before acknowledgement message was received at STREAM head.
- EAGAIN or ENOSR
-
Unable to allocate STREAMS storage to perform the I_PLINK.
- EBADF
-
The
arg
argument is not a valid, open file descriptor.
- EINVAL
-
The
fildes
argument does not support multiplexing; or
arg
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.
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
fildes.
In addition, an error code can be returned in the positive or negative
acknowledgement message. For these cases, I_PLINK shall fail with
errno
set to the value in the message.
- I_PUNLINK
-
Disconnects the two STREAMs specified by
fildes
and
arg
from a persistent connection. The
fildes
argument is the file descriptor of the STREAM connected to the
multiplexing driver. The
arg
argument is the multiplexer ID number that was returned by the I_PLINK
ioctl()
command when a STREAM was connected downstream from the multiplexing
driver. If
arg
is MUXID_ALL, then all STREAMs which are persistent connections
to
fildes
shall be disconnected. As in I_PLINK, this command requires the
multiplexing driver to acknowledge the request.
-
The
ioctl()
function with the I_PUNLINK command shall fail if:
- ENXIO
-
Hangup received on
fildes.
- ETIME
-
Timeout before acknowledgement message was received at STREAM head.
- EAGAIN or ENOSR
-
Unable to allocate buffers for the acknowledgement message.
- EINVAL
-
Invalid multiplexer ID number.
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
fildes.
In addition, an error code can be returned in the positive or negative
acknowledgement message. For these cases, I_PUNLINK shall fail with
errno
set to the value in the message.
RETURN VALUE
Upon successful completion,
ioctl()
shall return a value other than -1 that depends upon the STREAMS device
control function. Otherwise, it shall return -1 and set
errno
to indicate the error.
ERRORS
Under the following general conditions,
ioctl()
shall fail if:
- EBADF
-
The
fildes
argument is not a valid open file descriptor.
- EINTR
-
A signal was caught during the
ioctl()
operation.
- EINVAL
-
The STREAM or multiplexer referenced by
fildes
is linked (directly or indirectly) downstream from a multiplexer.
If an underlying device driver detects an error, then
ioctl()
shall fail if:
- EINVAL
-
The
request
or
arg
argument is not valid for this device.
- EIO
-
Some physical I/O error has occurred.
- ENOTTY
-
The file associated with the
fildes
argument is not a STREAMS device that accepts control functions.
- ENXIO
-
The
request
and
arg
arguments are valid for this device driver, but the service requested
cannot be performed on this particular sub-device.
- ENODEV
-
The
fildes
argument refers to a valid STREAMS device, but the corresponding device
driver does not support the
ioctl()
function.
If a STREAM is connected downstream from a multiplexer, any
ioctl()
command except I_UNLINK and I_PUNLINK shall set
errno
to
[EINVAL].
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The implementation-defined timeout interval for STREAMS has
historically been 15 seconds.
RATIONALE
None.
FUTURE DIRECTIONS
The
ioctl()
function may be removed in a future version.
SEE ALSO
Section 2.6,
STREAMS,
close(),
fcntl(),
getmsg(),
open(),
pipe(),
poll(),
putmsg(),
read(),
sigaction(),
write()
The Base Definitions volume of POSIX.1-2017,
<stropts.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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 .
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 .