streamio(7) DG/UX R4.11MU05 streamio(7)
NAME
streamio - STREAMS ioctl commands
SYNOPSIS
#include <sys/types.h>
#include <stropts.h>
int ioctl (int fildes, int command, ... /* arg */);
DESCRIPTION
STREAMS [see intro(2)] ioctl commands are a subset of the ioctl(2)
system calls which perform a variety of control functions on streams.
fildes is an open file descriptor that refers to a stream. command
determines the control function to be performed as described below.
arg represents additional information that is needed by this command.
The type of arg depends upon the command, but it is generally an
integer or a pointer to a command-specific data structure. The
command and arg are interpreted by the stream head. Certain
combinations of these arguments may be passed to a module or driver
in the stream.
Since these STREAMS commands are a subset of ioctl, they are subject
to the errors described there. In addition to those errors, the call
will fail with errno set to EINVAL, without processing a control
function, if the stream referenced by fildes is linked below a
multiplexor, or if command is not a valid value for a stream.
Also, as described in ioctl, STREAMS modules and drivers can detect
errors. In this case, the module or driver sends an error message to
the stream head containing an error value. This causes subsequent
system calls to fail with errno set to this value.
COMMAND FUNCTIONS
The following ioctl commands, with error values indicated, are
applicable to all STREAMS files:
IPUSH Pushes the module whose name is pointed to by arg onto
the top of the current stream, just below the stream
head. If the stream is a pipe, the module will be
inserted between the stream heads of both ends of the
pipe. It then calls the open routine of the newly-
pushed module. On failure, errno is set to one of the
following values:
EINVAL Invalid module name.
EFAULT arg points outside the allocated address
space.
ENXIO Open routine of new module failed.
ENXIO Hangup received on fildes.
IPOP Removes the module just below the stream head of the
stream pointed to by fildes. To remove a module from a
pipe requires that the module was pushed on the side it
is being removed from. arg should be 0 in an IPOP
request. On failure, errno is set to one of the
following values:
EINVAL No module present in the stream.
ENXIO Hangup received on fildes.
ILOOK Retrieves the name of the module just below the stream
head of the stream pointed to by fildes, and places it
in a null terminated character string pointed at by arg.
The buffer pointed to by arg should be at least
FMNAMESZ+1 bytes long. An (#include <sys/conf.h>)
declaration is required. On failure, errno is set to
one of the following values:
EFAULT arg points outside the allocated address
space.
EINVAL No module present in stream.
IFLUSH This request flushes all input and/or output queues,
depending on the value of arg. Legal arg values are:
FLUSHR Flush read queues.
FLUSHW Flush write queues.
FLUSHRW Flush read and write queues.
If a pipe or FIFO does not have any modules pushed, the
read queue of the stream head on either end is flushed
depending on the value of arg.
If FLUSHR is set and fildes is a pipe, the read queue
for that end of the pipe is flushed and the write queue
for the other end is flushed. If fildes is a FIFO, both
queues are flushed.
If FLUSHW is set and fildes is a pipe and the other end
of the pipe exists, the read queue for the other end of
the pipe is flushed and the write queue for this end is
flushed. If fildes is a FIFO, both queues of the FIFO
are flushed.
If FLUSHRW is set, all read queues are flushed, that is,
the read queue for the FIFO and the read queue on both
ends of the pipe are flushed.
Correct flush handling of a pipe 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 STREAMS memory
resources.
EINVAL Invalid arg value.
ENXIO Hangup received on fildes.
IFLUSHBAND Flushes a particular band of messages. arg points to a
bandinfo structure that has the following members:
unsigned char bipri;
int biflag;
The biflag field may be one of FLUSHR, FLUSHW, or
FLUSHRW as described earlier.
ISETSIG Informs the stream head that the user wishes the kernel
to issue the SIGPOLL signal [see signal(2)] when a
particular event has occurred on the stream associated
with fildes. ISETSIG supports an asynchronous
processing capability in STREAMS. The value of arg is a
bitmask that specifies the events for which the user
should be signaled. It is the bitwise-OR of any
combination of the following constants:
SINPUT Any message other than an MPCPROTO has
arrived on a stream head read queue. This
event is maintained for compatibility with
prior UNIX System V releases. This is set
even if the message is of zero length.
SRDNORM An ordinary (non-priority) message has
arrived on a stream head read queue. This
is set even if the message is of zero
length.
SRDBAND A priority band message (band > 0) has
arrived on a stream head read queue. This
is set even if the message is of zero
length.
SHIPRI A high priority message is present on the
stream head read queue. This is set even
if the message is of zero length.
SOUTPUT The write queue just below the stream head
is no longer full. This notifies the user
that there is room on the queue for sending
(or writing) data downstream.
SWRNORM This event is the same as SOUTPUT.
SWRBAND A priority band greater than 0 of a queue
downstream exists and is writable. This
notifies the user that there is room on the
queue for sending (or writing) priority
data downstream.
SMSG A STREAMS signal message that contains the
SIGPOLL signal has reached the front of the
stream head read queue.
SERROR An MERROR message has reached the stream
head.
SHANGUP An MHANGUP message has reached the stream
head.
SBANDURG When used in conjunction with SRDBAND,
SIGURG is generated instead of SIGPOLL when
a priority message reaches the front of the
stream head read queue.
A user process may choose to be signaled only of high
priority messages by setting the arg bitmask to the
value SHIPRI.
Processes that wish to receive SIGPOLL signals must
explicitly register to receive them using ISETSIG. If
several processes register to receive this signal for
the same event on the same stream, each process will be
signaled when the event occurs.
If the value of arg is zero, the calling process will be
unregistered and will not receive further SIGPOLL
signals. On failure, errno is set to one of the
following values:
EINVAL arg value is invalid or arg is zero and
process is not registered to receive the
SIGPOLL signal.
EAGAIN Allocation of a data structure to store the
signal request failed.
IGETSIG Returns the events for which the calling process is
currently registered to be sent a SIGPOLL signal. The
events are returned as a bitmask pointed to by arg,
where the events are those specified in the description
of ISETSIG above. On failure, errno is set to one of
the following values:
EINVAL Process not registered to receive the
SIGPOLL signal.
EFAULT arg points outside the allocated address
space.
IFIND Compares the names of all modules currently present in
the stream to the name pointed to by arg, and returns 1
if the named module is present in the stream. It
returns 0 if the named module is not present. On
failure, errno is set to one of the following values:
EFAULT arg points outside the allocated address
space.
EINVAL arg does not contain a valid module name.
IPEEK Allows a user to retrieve the information in the first
message on the stream head read queue without taking the
message off the queue. IPEEK is analogous to getmsg(2)
except that it does not remove the message from the
queue. arg points to a strpeek structure which contains
the following members:
struct strbufctlbuf;
struct strbufdatabuf;
long flags;
The maxlen field in the ctlbuf and databuf strbuf
structures [see getmsg(2)] must be set to the number of
bytes of control information and/or data information,
respectively, to retrieve. flags may be set to RSHIPRI
or 0. If RSHIPRI is set, IPEEK will look for a high
priority message on the stream head read queue.
Otherwise, IPEEK will look for the first message on the
stream head read queue.
IPEEK returns 1 if a message was retrieved, and returns
0 if no message was found on the stream head read queue.
It does not wait for a message to arrive. On return,
ctlbuf specifies information in the control buffer,
databuf specifies information in the data buffer, and
flags contains the value RSHIPRI or 0. On failure,
errno is set to the following value:
EFAULT arg points, or the buffer area specified in
ctlbuf or databuf is, outside the allocated
address space.
EBADMSG Queued message to be read is not valid for
IPEEK
EINVAL Illegal value for flags.
ISRDOPT Sets the read mode [see read(2)] using the value of the
argument arg. Legal arg values are:
RNORM Byte-stream mode, the default.
RMSGD Message-discard mode.
RMSGN Message-nondiscard mode.
In addition, treatment of control messages by the stream
head may be changed by setting the following flags in
arg:
RPROTNORM Fail read() with EBADMSG if a control
message is at the front of the stream head
read queue. This is the default behavior.
RPROTDAT Deliver the control portion of a message as
data when a user issues read().
RPROTDIS Discard the control portion of a message,
delivering any data portion, when a user
issues a read().
On failure, errno is set to the following value:
EINVAL arg is not one of the above legal values.
IGRDOPT Returns the current read mode setting in an int pointed
to by the argument arg. Read modes are described in
read(2). On failure, errno is set to the following
value:
EFAULT arg points outside the allocated address
space.
INREAD Counts the number of data bytes in data blocks in the
first message on the stream head read queue, and places
this value in the location pointed to by arg. The
return value for the command is the number of messages
on the stream head read queue. For example, if zero is
returned in arg, but the ioctl return value is greater
than zero, this indicates that a zero-length message is
next on the queue. On failure, errno is set to the
following value:
EFAULT arg points outside the allocated address
space.
IFDINSERT Creates a message from user specified buffer(s), adds
information about another stream and sends the message
downstream. The message contains a control part and an
optional data part. The data and control parts to be
sent are distinguished by placement in separate buffers,
as described below.
arg points to a strfdinsert structure which contains the
following members:
struct strbufctlbuf;
struct strbufdatabuf;
long flags;
int fildes;
int offset;
The len field in the ctlbuf strbuf structure [see
putmsg(2)] must be set to the size of a pointer plus the
number of bytes of control information to be sent with
the message. fildes in the strfdinsert structure
specifies the file descriptor of the other stream.
offset, which must be word-aligned, specifies the number
of bytes beyond the beginning of the control buffer
where IFDINSERT will store a pointer. This pointer
will be the address of the read queue structure of the
driver for the stream corresponding to fildes in the
strfdinsert structure. The len field in the databuf
strbuf structure must be set to the number of bytes of
data information to be sent with the message or zero if
no data part is to be sent.
flags specifies the type of message to be created. An
ordinary (non-priority) message is created if flags is
set to 0, a high priority message is created if flags is
set to RSHIPRI. For normal messages, IFDINSERT will
block if the stream write queue is full due to internal
flow control conditions. For high priority messages,
IFDINSERT does not block on this condition. For normal
messages, IFDINSERT does not block when the write queue
is full and ONDELAY or ONONBLOCK is set. Instead, it
fails and sets errno to EAGAIN.
IFDINSERT also blocks, unless prevented by lack of
internal resources, waiting for the availability of
message blocks, regardless of priority or whether
ONDELAY or ONONBLOCK has been specified. No partial
message is sent. On failure, errno is set to one of the
following values:
EAGAIN A non-priority message was specified, the
ONDELAY or ONONBLOCK flag is set, and the
stream write queue is full due to internal
flow control conditions.
ENOSR Buffers could not be allocated for the
message that was to be created due to
insufficient STREAMS memory resources.
EFAULT arg points, or the buffer area specified in
ctlbuf or databuf is, outside the allocated
address space.
EINVAL One of the following: fildes in the
strfdinsert structure is not a valid, open
stream file descriptor; the size of a
pointer plus offset is greater than the len
field for the buffer specified through
ctlptr; offset does not specify a properly-
aligned location in the data buffer; an
undefined value is stored in flags.
ENXIO Hangup received on fildes of the ioctl call
or fildes in the strfdinsert structure.
ERANGE The len field for the buffer specified
through databuf does not fall within the
range specified by the maximum and minimum
packet sizes of the topmost stream module,
or the len field for the buffer specified
through databuf is larger than the maximum
configured size of the data part of a
message, or the len field for the buffer
specified through ctlbuf is larger than the
maximum configured size of the control part
of a message.
IFDINSERT can also fail if an error message was
received by the stream head of the stream corresponding
to fildes in the strfdinsert structure. In this case,
errno will be set to the value in the message.
ISTR Constructs an internal STREAMS ioctl message from the
data pointed to by arg, and sends that message
downstream.
This mechanism is provided to send user ioctl requests
to downstream modules and drivers. It allows
information to be sent with the ioctl, and will return
to the user any information sent upstream by the
downstream recipient. ISTR blocks until the system
responds with either a positive or negative
acknowledgement message, or until the request "times
out" after some period of time. If the request times
out, it fails with errno set to ETIME.
At most, one ISTR can be active on a stream. Further
ISTR calls will block until the active ISTR completes
at the stream head. The default timeout interval for
these requests is 15 seconds. The ONDELAY and
ONONBLOCK [see open(2)] flags have no effect on this
call.
To send requests downstream, arg must point to a
strioctl structure which contains the following members:
int iccmd;
int ictimout;
int iclen;
char *icdp;
iccmd is the internal ioctl command intended for a
downstream module or driver and ictimout is the number
of seconds (-1 = infinite, 0 = use default, >0 = as
specified) an ISTR request will wait for
acknowledgement before timing out. The default timeout
is infinite. iclen is the number of bytes in the data
argument and icdp is a pointer to the data argument.
The iclen field has two uses: on input, it contains the
length of the data argument passed in, and on return
from the command, it contains the number of bytes being
returned to the user (the buffer pointed to by icdp
should be large enough to contain the maximum amount of
data that any module or the driver in the stream can
return).
The stream head will convert the information pointed to
by the strioctl structure to an internal ioctl command
message and send it downstream. On failure, errno is
set to one of the following values:
ENOSR Unable to allocate buffers for the ioctl
message due to insufficient STREAMS memory
resources.
EFAULT arg points, or the buffer area specified by
icdp and iclen (separately for data sent
and data returned) is, outside the
allocated address space.
EINVAL iclen is less than 0 or iclen is larger
than the maximum configured size of the
data part of a message or ictimout is less
than -1.
ENXIO Hangup received on fildes.
ETIME A downstream ioctl timed out before
acknowledgement was received.
An ISTR can also fail while waiting for an
acknowledgement if a message indicating an error or a
hangup is received at the stream head. In addition, an
error code can be returned in the positive or negative
acknowledgement message, in the event the ioctl command
sent downstream fails. For these cases, ISTR will fail
with errno set to the value in the message.
ISWROPT Sets the write mode using the value of the argument arg.
Legal bit settings for arg are:
SNDPIPE Send a SIGPIPE when a write is attempted on
a hung-up stream or is attempted on a
stream with a write error. By default,
this option is not enabled.
SNDZERO Send a zero-length message downstream when
a write of 0 bytes occurs. This option
only pertains to stream pipes and FIFOs.
By default, it is not enabled.
To not send a zero-length message when a write of 0
bytes occurs, this bit must not be set in arg.
On failure, errno may be set to the following value:
EINVAL arg is the the above legal value.
IGWROPT Returns the current write mode setting, as described
above, in the int that is pointed to by the argument
arg.
ISENDFD Requests the stream associated with fildes to send a
message, containing a file pointer, to the stream head
at the other end of a stream pipe. The file pointer
corresponds to arg, which must be an open file
descriptor.
ISENDFD converts arg into the corresponding system file
pointer. It allocates a message block and inserts the
file pointer in the block. The user id and group id
associated with the sending process are also inserted.
This message is placed directly on the read queue [see
intro(2)] of the stream head at the other end of the
stream pipe to which it is connected. On failure, errno
is set to one of the following values:
EAGAIN The sending stream is unable to allocate a
message block to contain the file pointer.
EAGAIN The read queue of the receiving stream head
is full and cannot accept the message sent
by ISENDFD.
EBADF arg is not a valid, open file descriptor.
EINVAL fildes is not connected to a stream pipe.
ENXIO Hangup received on fildes.
IRECVFD Retrieves the file descriptor associated with the
message sent by an ISENDFD ioctl over a stream pipe.
arg is a pointer to a data buffer large enough to hold
an strrecvfd data structure containing the following
members:
int fd;
uidt uid;
gidt gid;
char fill[8];
fd is an integer file descriptor. uid and gid are the
user id and group id, respectively, of the sending
stream.
If ONDELAY and ONONBLOCK are clear [see open(2)],
IRECVFD will block until a message is present at the
stream head. If ONDELAY or ONONBLOCK is set, IRECVFD
will fail with errno set to EAGAIN if no message is
present at the stream head.
If the message at the stream head is a message sent by
an ISENDFD, a new user file descriptor is allocated for
the file pointer contained in the message. The new file
descriptor is placed in the fd field of the strrecvfd
structure. The structure is copied into the user data
buffer pointed to by arg. On failure, errno is set to
one of the following values:
EAGAIN A message is not present at the stream head
read queue, and the ONDELAY or ONONBLOCK
flag is set.
EBADMSG The message at the stream head read queue
is not a message containing a passed file
descriptor.
EFAULT arg points outside the allocated address
space.
EMFILE NOFILES file descriptors are currently
open.
ENXIO Hangup received on fildes.
EOVERFLOW uid or gid is too large to be stored in the
structure pointed to by arg.
ILIST Allows the user to list all the module names on the
stream, up to and including the topmost driver name. If
arg is NULL, the return value is the number of modules,
including the driver, that are on the stream pointed to
by fildes. This allows the user to allocate enough
space for the module names. If arg is non-NULL, it
should point to an strlist structure that has the
following members:
int slnmods;
struct strmlist *slmodlist;
The strmlist structure has the following member:
char lname[FMNAMESZ+1];
slnmods indicates the number of entries the user has
allocated in the array and on return, slmodlist
contains the list of module names. The return value
indicates the number of entries that have been filled
in. On failure, errno may be set to one of the
following values:
EINVAL The slnmods member is less than 1.
EAGAIN Unable to allocate buffers
IATMARK Allows the user to see if the current message on the
stream head read queue is "marked" by some module
downstream. arg determines how the checking is done
when there may be multiple marked messages on the stream
head read queue. It may take the following values:
ANYMARK Check if the message is marked.
LASTMARK Check if the message is the last one marked
on the queue.
The return value is 1 if the mark condition is satisfied
and 0 otherwise. On failure, errno may be set to the
following value:
EINVAL Invalid arg value.
ICKBAND Check if the message of a given priority band exists on
the stream head read queue. This returns 1 if a message
of a given priority exists, or -1 on error. arg should
be an integer containing the value of the priority band
in question. On failure, errno may be set to the
following value:
EINVAL Invalid arg value.
IGETBAND Returns the priority band of the first message on the
stream head read queue in the integer referenced by arg.
On failure, errno may be set to the following value:
ENODATA No message on the stream head read queue.
ICANPUT Check if a certain band is writable. arg is set to the
priority band in question. The return value is 0 if the
priority band arg is flow controlled, 1 if the band is
writable, or -1 on error. On failure, errno may be set
to the following value:
EINVAL Invalid arg value.
ISETCLTIME Allows the user to set the time the stream head will
delay when a stream is closing and there are data on the
write queues. Before closing each module and driver,
the stream head will delay for the specified amount of
time to allow the data to drain. If, after the delay,
data are still present, data will be flushed. arg is a
pointer to the number of milliseconds to delay, rounded
up to the nearest legal value on the system. The
default is fifteen seconds. On failure, errno may be
set to the following value:
EINVAL Invalid arg value.
IGETCLTIME Returns the close time delay in the long pointed by arg.
The following four commands are used for connecting and disconnecting
multiplexed STREAMS configurations.
ILINK Connects two streams, where fildes is the file
descriptor of the stream connected to the multiplexing
driver, and arg is the file descriptor of the stream
connected to another driver. The stream designated by
arg gets connected below the multiplexing driver.
ILINK requires the multiplexing driver to send an
acknowledgement message to the stream head regarding the
linking operation. This call returns a multiplexor ID
number (an identifier used to disconnect the
multiplexor, see IUNLINK) on success, and a -1 on
failure. On failure, errno is set to one of the
following values:
ENXIO Hangup received on fildes.
ETIME Time out before acknowledgement message was
received at stream head.
EAGAIN Temporarily unable to allocate storage to
perform the ILINK.
ENOSR Unable to allocate storage to perform the
ILINK due to insufficient STREAMS memory
resources.
EBADF arg is not a valid, open file descriptor.
EINVAL fildes stream does not support
multiplexing.
EINVAL arg is not a stream, or is already linked
under a multiplexor.
EINVAL The specified link operation would cause a
"cycle" in the resulting configuration;
that is, if a given driver is linked into a
multiplexing configuration in more than one
place.
EINVAL fildes is the file descriptor of a pipe or
FIFO.
An ILINK can also fail while waiting for the
multiplexing driver to acknowledge the link request, if
a message indicating an error or a hangup is received at
the stream head of fildes. In addition, an error code
can be returned in the positive or negative
acknowledgement message. For these cases, ILINK will
fail with errno set to the value in the message.
IUNLINK Disconnects the two streams specified by fildes and arg.
fildes is the file descriptor of the stream connected to
the multiplexing driver. arg is the multiplexor ID
number that was returned by the ILINK. If arg is -1,
then all Streams which were linked to fildes are
disconnected. As in ILINK, this command requires the
multiplexing driver to acknowledge the unlink. On
failure, errno is set to one of the following values:
ENXIO Hangup received on fildes.
ETIME Time out before acknowledgement message was
received at stream head.
ENOSR Unable to allocate storage to perform the
IUNLINK due to insufficient STREAMS memory
resources.
EINVAL arg is an invalid multiplexor ID number or
fildes is not the stream on which the
ILINK that returned arg was performed.
EINVAL fildes is the file descriptor of a pipe or
FIFO.
An IUNLINK can also fail while waiting for the
multiplexing driver to acknowledge the link request, if
a message indicating an error or a hangup is received at
the stream head of fildes. In addition, an error code
can be returned in the positive or negative
acknowledgement message. For these cases, IUNLINK will
fail with errno set to the value in the message.
IPLINK Connects two streams, where fildes is the file
descriptor of the stream connected to the multiplexing
driver, and arg is the file descriptor of the stream
connected to another driver. The stream designated by
arg gets connected via a persistent link below the
multiplexing driver. IPLINK requires the multiplexing
driver to send an acknowledgement message to the stream
head regarding the linking operation. This call creates
a persistent link which can exist even if the file
descriptor fildes associated with the upper stream to
the multiplexing driver is closed. This call returns a
multiplexor ID number (an identifier that may be used to
disconnect the multiplexor, see IPUNLINK) on success,
and a -1 on failure. On failure, errno may be set to
one of the following values:
ENXIO Hangup received on fildes.
ETIME Time out before acknowledgement message was
received at the stream head.
EAGAIN Unable to allocate STREAMS storage to
perform the IPLINK.
EBADF arg is not a valid, open file descriptor.
EINVAL fildes does not support multiplexing.
EINVAL arg is not a stream or is already linked
under a multiplexor.
EINVAL The specified link operation would cause a
"cycle" in the resulting configuration;
that is, if a given stream head is linked
into a multiplexing configuration in more
than one place.
EINVAL fildes is the file descriptor of a pipe or
FIFO.
An IPLINK can also fail while waiting for the
multiplexing driver to acknowledge the link request, if
a message indicating an error on a hangup is received at
the stream head of fildes. In addition, an error code
can be returned in the positive or negative
acknowledgement message. For these cases, IPLINK will
fail with errno set to the value in the message.
IPUNLINK Disconnects the two streams specified by fildes and arg
that are connected with a persistent link. fildes is
the file descriptor of the stream connected to the
multiplexing driver. arg is the multiplexor ID number
that was returned by IPLINK when a stream was linked
below the multiplexing driver. If arg is MUXIDALL then
all streams which are persistent links to fildes are
disconnected. As in IPLINK, this command requires the
multiplexing driver to acknowledge the unlink. On
failure, errno may be set to one of the following
values:
ENXIO Hangup received on fildes.
ETIME Time out before acknowledgement message was
received at the stream head.
EAGAIN Unable to allocate buffers for the
acknowledgement message.
EINVAL Invalid multiplexor ID number.
EINVAL fildes is the file descriptor of a pipe or
FIFO.
An IPUNLINK can also fail while waiting for the
multiplexing driver to acknowledge the link request if a
message indicating an error or a hangup is received at
the stream head of fildes. In addition, an error code
can be returned in the positive or negative
acknowledgement message. For these cases, IPUNLINK
will fail with errno set to the value in the message.
SEE ALSO
close(2), fcntl(2), getmsg(2), intro(2), ioctl(2), open(2), poll(2),
putmsg(2), read(2), signal(2), write(2), signal(5).
Programmer's Guide: STREAMS.
DIAGNOSTICS
Unless specified otherwise above, the return value from ioctl is 0
upon success and -1 upon failure with errno set as indicated.
Licensed material--property of copyright holder(s)