streamio(M) 19 June 1992 streamio(M) Name streamio - STREAMS ioctl commands Syntax #include<stropts.h> int ioctl (fildes, command, arg) int fildes, command; Description STREAMS (see intro(S)) ioctl commands are a subset of ioctl(S) system calls which perform a variety of control functions on ``streams''. The arguments command and arg are passed to the file designated by fildes and are interpreted by the ``stream head''. Certain combinations of these arguments may be passed to a module or driver in the stream. 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. 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 multiplexer, or if com- mand 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. 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. 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, depend- ing on the value of arg. Legal arg values are: FLUSHR Flush read queues. FLUSHW Flush write queues. FLUSHRW Flush read and write queues. 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. ISETSIG Informs the stream head that the user wishes the kernel to issue the SIGPOLL signal (see signal(S) and sigset(S)) 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 A non-priority message has arrived on a stream head read queue, and no other messages existed on that queue before this message was placed there. This is set even if the message is of zero length. SHIPRI A priority message is present on the stream head read queue. This is set even if the mes- sage 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. SMSG A STREAMS signal message that contains the SIG- POLL signal has reached the front of the stream head read queue. A user process may choose to be signaled only of priority messages by setting the arg bitmask to the value SHIPRI. Processes that wish to receive SIGPOLL signals must explic- itly 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 sig- nal. [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 fol- lowing 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 mes- sage on the stream head read queue without taking the mes- sage off 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 structures (see getmsg(S)) must be set to the number of bytes of con- trol information and/or data information, respectively, to retrieve. If the user sets flags to RSHIPRI, IPEEK will only look for a priority 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, or if the RSHIPRI flag was set in flags and a 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 infor- mation in the data buffer, and flags contains the value 0 or RSHIPRI. On failure, errno is set to one of the following values: [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 ISRDOPT Sets the read mode 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. Read modes are described in read(S). 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(S). 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 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 dis- tinguished by placement in separate buffers, as described below. arg points to a strfdinsert structure which contains the following members: struct strbuf ctlbuf; struct strbuf databuf; long flags; int fildes; int offset; The len field in the ctlbuf strbuf structure (see putmsg(S)) 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. A non- priority message is created if flags is set to 0, and a priority message is created if flags is set to RSHIPRI. For non-priority messages, IFDINSERT will block if the stream write queue is full due to internal flow control con- ditions. For priority messages, IFDINSERT does not block on this condition. For non-priority messages, IFDINSERT does not block when the write queue is full and ONDELAY 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 in the stream, regardless of priority or whether ONDELAY 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 flag is set, and the stream write queue is full due to internal flow control con- ditions. [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 speci- fied 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 informa- tion sent upstream by the downstream recipient. ISTR blocks until the system responds with either a positive or negative acknowledgment 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 (see open(S)) flag has no effect on this call. To send requests downstream, arg must point to a strioctl structure which contains the following members: int ic_cmd; /* downstream command */ int ic_timout; /* ACK/NAK timeout */ int ic_len; /* length of data arg */ char *ic_dp; /* ptr to data arg */ iccmd is the internal ioctl command intended for a down- stream module or driver; and ictimout is the number of seconds (-1 = infinite, 0 = use default, >0 = as specified) an ISTR request will wait for acknowledgment before timing out. 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 con- tains 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 mes- sage 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 acknowledg- ment was received. An ISTR can also fail while waiting for an acknowledgment 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 acknowledgment message, in the event that the ioctl command sent downstream fails. For these cases, ISTR will fail with errno set to the value in the message. ISENDFD Requests the stream associated with fildes to send a mes- sage, 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 integer 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(S)) 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 fol- lowing values: [EAGAIN] The sending stream is unable to allocate a mes- sage 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; unsigned short uid; unsigned short 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 is not set (see open(S)), IRECVFD will block until a message is present at the stream head. If ONDELAY 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 struc- ture. 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 was not present at the stream head read queue, and the ONDELAY flag is set. [EBADMSG] The message at the stream head read queue was not a message containing a passed file descrip- tor. [EFAULT] arg points outside the allocated address space. [EMFILE] No files file descriptors are currently open. [ENXIO] Hangup received on fildes. The following two commands are used for connecting and disconnecting mul- tiplexed 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 acknowledgment message to the stream head regarding the linking operation. This call returns a multi- plexer ID number (an identifier used to disconnect the mul- tiplexer, 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 acknowledgment message was received at stream head. [EAGAIN] Temporarily unable to allocate storage to per- form 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 multiplexer. [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. An ILINK 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 acknowledgment 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. fildes must correspond to the stream on which the ioctl ILINK command was issued to link the stream below the multiplexing driver. arg is the multi- plexer ID number that was returned by the ILINK. If arg is -1, then all streams which were linked to fildes are discon- nected. As in ILINK, this command requires the multiplex- ing 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 acknowledgment 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 multiplexer ID number or fildes is not the stream on which the ILINK that returned arg was performed. An IUNLINK 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 acknowledgment message. For these cases, IUNLINK will fail with errno set to the value in the message. See also close(S), fcntl(S), getmsg(S), intro(S), ioctl(S), open(S), poll(S), putmsg(S), read(S), signal(S), sigset(S), write(S) STREAMS Programmer's Guide STREAMS Primer Diagnostics Unless specified otherwise above, the return value from ioctl is 0 upon success and -1 upon failure with errno set as indicated.