STREAMIO(7I)STREAMIO(7I)NAMEstreamio - STREAMS ioctl commands
SYNOPSIS
#include <sys/types.h>
#include <stropts.h>
#include <sys/conf.h>
int ioctl(int fildes, int command, ... /*arg*/);
DESCRIPTION
STREAMS (see Intro(3)) ioctl commands are a subset of the ioctl(2) com‐
mands and perform a variety of control functions on streams.
The fildes argument is an open file descriptor that refers to a stream.
The command argument determines the control function to be performed as
described below. The arg argument represents additional information
that is needed by this command. The type of arg depends upon the com‐
mand, but it is generally an integer or a pointer to a command-specific
data structure. The command and arg arguments are interpreted by the
STREAM head. Certain combinations of these arguments may be passed to
a module or driver in the stream.
Since these STREAMS commands are ioctls, they are subject to the errors
described in ioctl(2). In addition to those errors, the call will fail
with errno set to EINVAL, without processing a control function, if the
STREAM referenced by fildes is linked below a multiplexor, or if com‐
mand is not a valid value for a stream.
Also, as described in ioctl(2), STREAMS modules and drivers can detect
errors. In this case, the module or driver sends an error message to
the STREAM head containing an error value. This causes subsequent calls
to fail with errno set to this value.
IOCTLS
The following ioctl commands, with error values indicated, are applica‐
ble 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. If the STREAM is a pipe, the module will be
inserted between the stream heads of both ends of the
pipe. It then calls the open routine of the newly-pushed
module. On failure, errno is set to one of the following
values:
EINVAL
Invalid module name.
EFAULT
arg points outside the allocated address
space.
ENXIO
Open routine of new module failed.
ENXIO
Hangup received on fildes.
ENOTSUP
Pushing a module is not supported on this
stream.
I_POP
Removes the module just below the STREAM head of the
STREAM pointed to by fildes. To remove a module from a
pipe requires that the module was pushed on the side it
is being removed from. arg should be 0 in an I_POP
request. On failure, errno is set to one of the follow‐
ing values:
EINVAL
No module present in the stream.
ENXIO
Hangup received on fildes.
EPERM
Attempt to pop through an anchor by an
unprivileged process.
ENOTSUP
Removal is not supported.
I_ANCHOR
Positions the stream anchor to be at the stream's module
directly below the stream head. Once this has been done,
only a privileged process may pop modules below the
anchor on the stream. arg must be 0 in an I_ANCHOR
request. On failure, errno is set to the following
value:
EINVAL
Request to put an anchor on a pipe.
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 null terminated character string pointed at by arg.
The buffer pointed to by arg should be at least
FMNAMESZ+1 bytes long. This requires the declaration
#include <sys/conf.h>. On failure, errno is set to one
of the following values:
EFAULT
arg points outside the allocated address
space.
EINVAL
No module present in stream.
I_FLUSH
This request flushes all input and/or output queues,
depending on the value of arg. Legal arg values are:
FLUSHR
Flush read queues.
FLUSHW
Flush write queues.
FLUSHRW
Flush read and write queues.
If a pipe or FIFO does not have any modules pushed, the
read queue of the stream head on either end is flushed
depending on the value of arg.
If FLUSHR is set and fildes is a pipe, the read queue
for that end of the pipe is flushed and the write queue
for the other end is flushed. If fildes is a FIFO, both
queues are flushed.
If FLUSHW is set and fildes is a pipe and the other end
of the pipe exists, the read queue for the other end of
the pipe is flushed and the write queue for this end is
flushed. If fildes is a FIFO, both queues of the FIFO
are flushed.
If FLUSHRW is set, all read queues are flushed, that is,
the read queue for the FIFO and the read queue on both
ends of the pipe are flushed.
Correct flush handling of a pipe or FIFO with modules
pushed is achieved via the pipemod module. This module
should be the first module pushed onto a pipe so that it
is at the midpoint of the pipe itself.
On failure, errno is set to one of the following values:
ENOSR
Unable to allocate buffers for flush message
due to insufficient stream memory resources.
EINVAL
Invalid arg value.
ENXIO
Hangup received on fildes.
I_FLUSHBAND
Flushes a particular band of messages. arg points to a
bandinfo structure that has the following members:
unsigned char bi_pri;
int bi_flag;
The bi_flag field may be one of FLUSHR, FLUSHW, or
FLUSHRW as described earlier.
I_SETSIG
Informs the stream head that the user wishes the kernel
to issue the SIGPOLL signal (see signal(3C)) when a par‐
ticular 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 user should be
signaled. It is the bitwise OR of any combination of the
following constants:
S_INPUT
Any message other than an M_PCPROTO has
arrived on a stream head read queue. This
event is maintained for compatibility with
previous releases. This event is triggered
even if the message is of zero length.
S_RDNORM
An ordinary (non-priority) message has
arrived on a stream head read queue. This
event is triggered even if the message is
of zero length.
S_RDBAND
A priority band message (band > 0) has
arrived on a stream head read queue. This
event is triggered even if the message is
of zero length.
S_HIPRI
A high priority message is present on the
stream head read queue. This event is trig‐
gered even if the message is of zero
length.
S_OUTPUT
The write queue just below the stream head
is no longer full. This notifies the user
that there is room on the queue for sending
(or writing) data downstream.
S_WRNORM
This event is the same as S_OUTPUT.
S_WRBAND
A priority band greater than 0 of a queue
downstream exists and is writable. This
notifies the user 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
An M_ERROR message has reached the stream
head.
S_HANGUP
An M_HANGUP message 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.
A user process may choose to be signaled only of high
priority messages by setting the arg bitmask to the
value S_HIPRI.
Processes that wish to receive SIGPOLL signals must
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 will be
signaled when the event occurs.
If the value of arg is zero, the calling process will be
unregistered and will not receive further SIGPOLL sig‐
nals. On failure, errno is set to one of the following
values:
EINVAL
arg value is invalid or arg is zero and
process is not registered to receive the SIG‐
POLL signal.
EAGAIN
Allocation of a data structure to store the
signal request failed.
I_GETSIG
Returns the events for which the calling process is cur‐
rently registered to be sent a SIGPOLL signal. The
events are returned as a bitmask pointed to by arg,
where the events are those specified in the description
of I_SETSIG above. On failure, errno is set to one of
the following values:
EINVAL
Process not registered to receive the SIGPOLL
signal.
EFAULT
arg points outside the allocated address
space.
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. It returns
0 if the named module is not present. On failure, errno
is set to one of the following values:
EFAULT
arg points outside the allocated address
space.
EINVAL
arg does not contain a valid module name.
I_PEEK
Allows a user to retrieve the information in the first
message on the stream head read queue without taking the
message off the queue. I_PEEK is analogous to getmsg(2)
except that it does not remove the message from the
queue. arg points to a strpeek structure, which contains
the following members:
struct strbuf ctlbuf;
struct strbuf databuf;
long flags;
The maxlen field in the ctlbuf and databuf strbuf struc‐
tures (see getmsg(2)) must be set to the number of bytes
of control information and/or data information, respec‐
tively, to retrieve. flags may be set to RS_HIPRI or 0.
If RS_HIPRI is set, I_PEEK will look for a high priority
message on the stream head read queue. Otherwise, I_PEEK
will look for the first 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.
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. On failure,
errno is set to the following value:
EFAULT
arg points, or the buffer area specified in
ctlbuf or databuf is, outside the allocated
address space.
EBADMSG
Queued message to be read is not valid for
I_PEEK.
EINVAL
Illegal value for flags.
ENOSR
Unable to allocate buffers to perform the
I_PEEK due to insufficient STREAMS memory
resources.
I_SRDOPT
Sets the read mode (see read(2)) using the value of the
argument arg. Legal arg values are:
RNORM
Byte-stream mode, the default.
RMSGD
Message-discard mode.
RMSGN
Message-nondiscard mode.
In addition, the stream head's treatment of control mes‐
sages may be changed by setting the following flags in
arg:
RPROTNORM
Reject read() with EBADMSG if a control
message is at the front of the stream head
read queue.
RPROTDAT
Deliver the control portion of a message as
data when a user issues read(). This is the
default behavior.
RPROTDIS
Discard the control portion of a message,
delivering any data portion, when a user
issues a read().
On failure, errno is set to the following value:
EINVAL
arg is not one of the above legal values, or
arg is the bitwise inclusive OR of RMSGD and
RMSGN.
I_GRDOPT
Returns the current read mode setting in an int pointed
to by the argument arg. Read modes are described in
read(). On failure, errno is set to the following value:
EFAULT
arg points outside the allocated address
space.
I_NREAD
Counts the number of data bytes in data blocks in the
first message on the stream head read queue, and places
this value in the location pointed to by arg. The return
value for the command is the number of messages on the
stream head read queue. For example, if zero is returned
in arg, but the ioctl return value is greater than zero,
this indicates that a zero-length message is next on the
queue. On failure, errno is set to the following value:
EFAULT
arg points outside the allocated address
space.
I_FDINSERT
Creates a message from specified buffer(s), adds infor‐
mation about another stream and sends the message down‐
stream. 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,
which contains the following members:
struct strbuf ctlbuf;
struct strbuf databuf;
t_uscalar_t flags;
int fildes;
int offset;
The len member in the ctlbuf strbuf structure (see
putmsg(2)) must be 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 mem‐
ber, 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 will store a t_uscalar_t
whose interpretation is specific to the stream end. The
len member in the databuf strbuf structure must be 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
will 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_NDELAY or 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 mes‐
sage blocks in the stream, regardless of priority or
whether O_NDELAY or O_NONBLOCK has been specified. No
partial message is sent.
The ioctl() function with the I_FDINSERT command will
fail if:
EAGAIN
A non-priority message is specified, the
O_NDELAY or O_NONBLOCK flag is set, and the
stream write queue is full due to internal
flow control conditions.
ENOSR
Buffers can not be allocated for the message
that is to be created.
EFAULT
The arg argument points, or the buffer area
specified in ctlbuf or databuf is, outside the
allocated address space.
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
ctlptr; the offset member does not specify a
properly-aligned location in the data buffer;
or an undefined value is stored in flags.
ENXIO
Hangup received on the fildes argument of the
ioctl call or the fildes member of the
strfdinsert structure.
ERANGE
The len field for the buffer specified through
databuf does not fall within the range speci‐
fied by the maximum and minimum packet sizes
of the topmost stream module; or the len mem‐
ber 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_FDINSERT can also fail if an error message was
received by the stream head of the stream corresponding
to the fildes member of the strfdinsert structure. In
this case, errno will be set to the value in the mes‐
sage.
I_STR
Constructs an internal STREAMS ioctl message from the
data pointed to by arg, and sends that message down‐
stream.
This mechanism is provided to send user ioctl requests
to downstream modules and drivers. It allows information
to be sent with the ioctl, and will return to the user
any information sent upstream by the downstream recipi‐
ent. I_STR blocks until the system responds with either
a positive or negative acknowledgement message, or until
the request times out after some period of time. If the
request times out, it fails with errno set to ETIME.
To send requests downstream, arg must point to a stri‐
octl structure which contains the following members:
int ic_cmd;
int ic_timout;
int ic_len;
char *ic_dp;
ic_cmd is the internal ioctl command intended for a
downstream module or driver and ic_timout is the number
of seconds (-1 = infinite, 0 = use default, >0 = as
specified) an I_STR request will wait for acknowledge‐
ment 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 field has two uses: on input, it
contains the length of the data argument passed in, and
on return from the command, it contains the number of
bytes being returned to the user (the buffer pointed to
by ic_dp should be large enough to contain the maximum
amount of data that any module or the driver in the
stream can return).
At most one I_STR can be active on a stream. Further
I_STR calls will block until the active I_STR completes
via a positive or negative acknowlegment, a timeout,
or an error condition at the stream head. By setting
the ic_timout field to 0, the user is requesting
STREAMS to provide the DEFAULT timeout. The default
timeout is specific to the STREAMS implementation and
may vary depending on which release of Solaris you are
using. For Solaris 8 (and earlier versions), the default
timeout is fifteen seconds. The O_NDELAY and O_NONBLOCK
(see open(2)) flags have no effect on this call.
The stream head will convert the information pointed to
by the strioctl structure to an internal ioctl command
message and send it downstream. On failure, errno is set
to one of the following values:
ENOSR
Unable to allocate buffers for the ioctl mes‐
sage due to insufficient STREAMS memory
resources.
EFAULT
Either arg points outside the allocated
address space, or the buffer area specified by
ic_dp and ic_len (separately for data sent and
data returned) is outside the allocated
address space.
EINVAL
ic_len is less than 0 or ic_len is 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 acknowl‐
edgement was received.
An I_STR can also fail while waiting for an acknowledge‐
ment 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 acknowledge‐
ment message, in the event the ioctl command sent down‐
stream fails. For these cases, I_STR will fail with
errno set to the value in the message.
I_SWROPT
Sets the write mode using the value of the argument arg.
Legal bit settings for arg are:
SNDZERO
Send a zero-length message downstream when a
write of 0 bytes occurs.
To not send a zero-length message when a write of 0
bytes occurs, this bit must not be set in arg.
On failure, errno may be set to the following value:
EINVAL
arg is not the above legal 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
Requests the stream associated with fildes to send a
message, containing a file pointer, to the stream head
at the other end of a stream pipe. The file pointer cor‐
responds to arg, which must be an open file descriptor.
I_SENDFD converts arg into the corresponding system file
pointer. It allocates a message block and inserts the
file pointer in the block. The user id and group id
associated with the sending process are also inserted.
This message is placed directly on the read queue (see
Intro(3)) of the stream head at the other end of the
stream pipe to which it is connected. On failure, errno
is set to one of the following values:
EAGAIN
The sending stream is unable to allocate a
message block to contain the file pointer.
EAGAIN
The read queue of the receiving stream head is
full and cannot accept the message sent by
I_SENDFD.
EBADF
arg is not a valid, open file descriptor.
EINVAL
fildes is not connected to a stream pipe.
ENXIO
Hangup received on fildes.
I_RECVFD
Retrieves the file descriptor associated with the mes‐
sage sent by an I_SENDFD ioctl over a stream pipe. arg
is a pointer to a data buffer large enough to hold an
strrecvfd data structure containing the following mem‐
bers:
int fd;
uid_t uid;
gid_t gid;
fd is an integer file descriptor. uid and gid are the
user id and group id, respectively, of the sending
stream.
If O_NDELAY and O_NONBLOCK are clear (see open(2)),
I_RECVFD will block until a message is present at the
stream head. If O_NDELAY or O_NONBLOCK is set, I_RECVFD
will fail with errno set to EAGAIN if no message is
present at the stream head.
If the message at the stream head is a message sent by
an I_SENDFD, a new user file descriptor is allocated for
the file pointer contained in the message. The new file
descriptor is placed in the fd field of the strrecvfd
structure. The structure is copied into the user data
buffer pointed to by arg. On failure, errno is set to
one of the following values:
EAGAIN
A message is not present at the stream head
read queue, and the O_NDELAY or O_NONBLOCK
flag is set.
EBADMSG
The message at the stream head read queue
is not a message containing a passed file
descriptor.
EFAULT
arg points outside the allocated address
space.
EMFILE
NOFILES file descriptors are currently
open.
ENXIO
Hangup received on fildes.
EOVERFLOW
uid or gid is too large to be stored in the
structure pointed to by arg.
I_LIST
Allows the user to list all the module names on the
stream, up to and including the topmost driver name. If
arg is NULL, the return value is the number of modules,
including the driver, that are on the stream pointed to
by fildes. This allows the user to allocate enough space
for the module names. If arg is non-null, it should
point to an str_list structure that has the following
members:
int sl_nmods;
struct str_mlist *sl_modlist;
The str_mlist structure has the following member:
char l_name[FMNAMESZ+1];
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 contains 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() is 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. On failure,
errno may be set to one of the following values:
EINVAL
The sl_nmods member is less than 1.
EAGAIN
Unable to allocate buffers
I_ATMARK
Allows the user to see if the current message on the
stream head read queue is ``marked'' by some module
downstream. arg determines how the checking is done when
there may be multiple marked messages on the stream head
read queue. It may take the following values:
ANYMARK
Check if the message is marked.
LASTMARK
Check if the message is the last one marked
on the queue.
The return value is 1 if the mark condition is satisfied
and 0 otherwise. On failure, errno is set to the follow‐
ing value:
EINVAL
Invalid arg value.
I_CKBAND
Check if the message of a given priority band exists on
the stream head read queue. This returns 1 if a message
of a given priority exists, 0 if not, or −1 on error.
arg should be an integer containing the value of the
priority band in question. On failure, errno is set to
the following value:
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.
On failure, errno is set to the following value:
ENODATA
No message on the stream head read queue.
I_CANPUT
Check if a certain band is writable. arg is set to the
priority band in question. The return value is 0 if the
priority band arg is flow controlled, 1 if the band is
writable, or −1 on error. On failure, errno is set to
the following value:
EINVAL
Invalid arg value.
I_SETCLTIME
Allows the user to set the time the stream head will
delay when a stream is closing and there are data on the
write queues. Before closing each module and driver,
the stream head will delay for the specified amount of
time to allow the data to drain. Note, however, that the
module or driver may itself delay in its close routine;
this delay is independent of the stream head's delay and
is not settable. If, after the delay, data are still
present, data will be flushed. arg is a pointer to an
integer containing the number of milliseconds to delay,
rounded up to the nearest legal value on the system.
The default is fifteen seconds. On failure, errno is set
to the following value:
EINVAL
Invalid arg value.
I_GETCLTIME
Returns the close time delay in the integer pointed by
arg.
I_SERROPT
Sets the error mode using the value of the argument arg.
Normally stream head errors are persistent; once they
are set due to an M_ERROR or M_HANGUP, the error condi‐
tion will remain until the stream is closed. This option
can be used to set the stream head into non-persistent
error mode i.e. once the error has been returned in
response to a read(2), getmsg(2), ioctl(2), write(2), or
putmsg(2) call the error condition will be cleared. The
error mode can be controlled independently for read and
write side errors. Legal arg values are either none or
one of:
RERRNORM
Persistent read errors, the default.
RERRNONPERSIST
Non-persistent read errors.
OR'ed with either none or one of:
WERRNORM
Persistent write errors, the default.
WERRNONPERSIST
Non-persistent write errors.
When no value is specified e.g. for
the read side error behavior then the
behavior for that side will be left
unchanged.
On failure, errno is set to the following value:
EINVAL
arg is not one of the above legal values.
I_GERROPT
Returns the current error mode setting in an int pointed
to by the argument arg. Error modes are described above
for I_SERROPT. On failure,errno is set to the following
value:
EFAULT
arg points outside the allocated address
space.
The following four commands are used for connecting and disconnecting
multiplexed STREAMS configurations.
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 gets con‐
nected below the multiplexing driver. I_LINK requires the
multiplexing driver to send an acknowledgement message to
the stream head regarding the linking operation. This call
returns a multiplexor ID number (an identifier used to
disconnect the multiplexor, see I_UNLINK) on success, and
-1 on failure. On failure, errno is set to one of the fol‐
lowing values:
ENXIO
Hangup received on fildes.
ETIME
Time out before acknowledgement message was
received at stream head.
EAGAIN
Temporarily unable to allocate storage to per‐
form the I_LINK.
ENOSR
Unable to allocate storage to perform the I_LINK
due to insufficient STREAMS memory resources.
EBADF
arg is not a valid, open file descriptor.
EINVAL
fildes stream does not support multiplexing.
EINVAL
arg is not a stream, or is already linked under
a multiplexor.
EINVAL
The specified link operation would cause a
``cycle'' in the resulting configuration; that
is, a driver would be linked into the multiplex‐
ing configuration in more than one place.
EINVAL
fildes is the file descriptor of a pipe or FIFO.
EINVAL
Either the upper or lower stream has a major
number >= the maximum major number on the sys‐
tem.
An I_LINK can also fail while waiting for the multiplexing
driver to acknowledge the link request, if a message indi‐
cating 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 will fail 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. arg is the multiplexor ID number
that was returned by the I_LINK. If arg is -1, then all
streams that were linked to fildes are disconnected. As
in I_LINK, this command requires the multiplexing driver
to acknowledge the unlink. On failure, errno is set to one
of the following values:
ENXIO
Hangup received on fildes.
ETIME
Time out before acknowledgement message was
received at stream head.
ENOSR
Unable to allocate storage to perform the
I_UNLINK due to insufficient STREAMS memory
resources.
EINVAL
arg is an invalid multiplexor ID number or
fildes is not the stream on which the I_LINK
that returned arg was performed.
EINVAL
fildes is the file descriptor of a pipe or FIFO.
An I_UNLINK can also fail while waiting for the multi‐
plexing driver to acknowledge the link request, if a mes‐
sage 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 mes‐
sage. For these cases, I_UNLINK will fail with errno set
to the value in the message.
I_PLINK
Connects two streams, where fildes is the file descriptor
of the stream connected to the multiplexing driver, and
arg is the file descriptor of the stream connected to
another driver. The stream designated by arg gets con‐
nected via a persistent link below the multiplexing
driver. I_PLINK requires the multiplexing driver to send
an acknowledgement message to the stream head regarding
the linking operation. This call creates a persistent link
that continues to exist even if the file descriptor fildes
associated with the upper stream to the multiplexing
driver is closed. This call returns a multiplexor ID num‐
ber (an identifier that may be used to disconnect the mul‐
tiplexor, see I_PUNLINK) on success, and -1 on failure.
On failure, errno is set to one of the following values:
ENXIO
Hangup received on fildes.
ETIME
Time out before acknowledgement message was
received at the stream head.
EAGAIN
Unable to allocate STREAMS storage to perform
the I_PLINK.
EBADF
arg is not a valid, open file descriptor.
EINVAL
fildes does not support multiplexing.
EINVAL
arg is not a stream or is already linked under a
multiplexor.
EINVAL
The specified link operation would cause a
``cycle'' in the resulting configuration; that
is, if a driver would be linked into the multi‐
plexing configuration in more than one place.
EINVAL
fildes is the file descriptor of a pipe or FIFO.
An I_PLINK can also fail while waiting for the multiplex‐
ing driver to acknowledge the link request, if a message
indicating an error on a hangup is received at the stream
head of fildes. In addition, an error code can be returned
in the positive or negative acknowledgement message. For
these cases, I_PLINK will fail with errno set to the value
in the message.
I_PUNLINK
Disconnects the two streams specified by fildes and arg
that are connected with a persistent link. fildes is the
file descriptor of the stream connected to the multiplex‐
ing driver. arg is the multiplexor ID number that was
returned by I_PLINK when a stream was linked below the
multiplexing driver. If arg is MUXID_ALL then all streams
that are persistent links to fildes are disconnected. As
in I_PLINK, this command requires the multiplexing driver
to acknowledge the unlink. On failure, errno is set to one
of the following values:
ENXIO
Hangup received on fildes.
ETIME
Time out before acknowledgement message was
received at the stream head.
EAGAIN
Unable to allocate buffers for the acknowledge‐
ment message.
EINVAL
Invalid multiplexor ID number.
EINVAL
fildes is the file descriptor of a pipe or FIFO.
An I_PUNLINK can also fail while waiting for the multi‐
plexing driver to acknowledge the link request if a mes‐
sage 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 mes‐
sage. For these cases, I_PUNLINK will fail with errno set
to the value in the message.
RETURN VALUES
Unless specified otherwise above, the return value from ioctl() is 0
upon success and −1 upon failure, with errno set as indicated.
SEE ALSOIntro(3), close(2), fcntl(2), getmsg(2), ioctl(2), open(2), poll(2),
putmsg(2), read(2), write(2), signal(3C), signal.h(3HEAD),
STREAMS Programming Guide
Apr 8, 2009 STREAMIO(7I)
