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

PROLOG         top

       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         top

       ioctl — control a STREAMS device (STREAMS)

SYNOPSIS         top

       #include <stropts.h>

       int ioctl(int fildes, int request, ... /* arg */);

DESCRIPTION         top

       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         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       The implementation-defined timeout interval for STREAMS has
       historically been 15 seconds.

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       The ioctl() function may be removed in a future version.

SEE ALSO         top

       Section 2.6, STREAMS, close(3p), fcntl(3p), getmsg(3p), open(3p),
       pipe(3p), poll(3p), putmsg(3p), read(3p), sigaction(3p), write(3p)

       The Base Definitions volume of POSIX.1‐2008, stropts.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                           IOCTL(3P)

Pages that refer to this page: signal.h(0p)stropts.h(0p)close(3p)read(3p)