IOCTL(3)                   POSIX Programmer's Manual                  IOCTL(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 .



IEEE/The Open Group                  2017                             IOCTL(3)
