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WSAIoctl

The Windows Sockets WSAIoctl function controls the mode of a socket.

int WSAIoctl (

SOCKET s,

DWORD dwIoControlCode,

LPVOID lpvInBuffer,

DWORD cbInBuffer,

LPVOID lpvOUTBuffer,

DWORD cbOUTBuffer,

LPDWORD lpcbBytesReturned,

LPWSAOVERLAPPED lpOverlapped,

LPWSAOVERLAPPED_COMPLETION_ROUTINE lpCompletionROUTINE

);

Parameters

s

[in] Handle to a socket

dwIoControlCode

[in] Control code of operation to perform

lpvInBuffer

[in] Address of input buffer

cbInBuffer

[in] Size of input buffer

lpvOutBuffer

[out] Address of output buffer

cbOutBuffer

[in] Size of output buffer

lpcbBytesReturned

[out] Address of actual bytes of output

lpOverlapped

[in] Address of WSAOVERLAPPED structure

lpCompletionRoutine

[in] A pointer to the completion routine called when the operation has been completed.

Remarks

This routine is used to set or retrieve operating parameters associated with the socket, the transport protocol, or the communications subsystem. For nonoverlapped socket, lpOverlapped and lpCompletionRoutine parameters are ignored, and this function behaves like the standard ioctlsocket function except that it may block if socket s is in the blocking mode. Note that if socket s is in the nonblocking mode, this function may return WSAEWOULDBLOCK if the specified operation cannot be finished immediately. In this case, the application should change the socket to the blocking mode and reissue the request. For overlapped sockets, operations that cannot be completed immediately will be initiated, and completion will be indicated at a later time. The final completion status is retrieved through WSAGetOverlappedResult. The lpcbBytesReturned parameter is ignored.

In as much as the dwIoControlCode parameter is now a 32-bit entity, it is possible to adopt an encoding scheme that preserves the currently defined ioctlsocket opcodes while providing a convenient way to partition the opcode identifier space. The dwIoControlCode parameter is architected to allow for protocol and vendor independence when adding new control codes, while retaining backward compatibility with the Windows Sockets 1.1 and Unix control codes. The dwIoControlCode parameter has the following form:

3
3
2
2 2
2 2 2 2 2 2 2 1 1 1 1
  1. 1 1 1 1 1

0
9
8 7
6 5 4 3 2 1 0 9 8 7 6
5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
I
O
V
T
Vendor/Address Family
Code

I is set if the input buffer is valid for the code, as with IOC_IN.

O is set if the output buffer is valid for the code, as with IOC_OUT. Note that for codes with both input and output parameters, both I and O will be set.

V is set if there are no parameters for the code, as with IOC_VOID.

T is a two-bit quantity which defines the type of ioctl. The following values are defined:

0 pics/SOCK200090001.gif The ioctl is a standard Unix ioctl code, as with FIONREAD and FIONBIO.

  1. pics/SOCK200090001.gif The ioctl is a generic Windows Sockets 2 ioctl code. New ioctl codes defined for Windows Sockets 2 will have T == 1.

  2. pics/SOCK200090001.gif The ioctl applies only to a specific address family.

  3. pics/SOCK200090001.gif The ioctl applies only to a specific vendor's provider. This type allows companies to be assigned a vendor number which appears in the

Vendor/Address family field, and then the vendor can define new ioctls specific to that vendor without having to register the ioctl with a clearinghouse, thereby providing vendor flexibility and privacy.

Vendor/Address family pics/SOCK200090001.gif An 11-bit quantity which defines the vendor who owns the code (if T == 3) or which contains the address family to which the code applies (if T == 2). If this is a Unix ioctl code (T == 0) then this field has the same value as the code on Unix. If this is a generic Windows Sockets 2 ioctl (T == 1) then this field can be used as an extension of the "code" field to provide additional code values.

Code pics/SOCK200090001.gif The specific ioctl code for the operation.

The following Unix commands are supported:

Parameters

FIONBIO

Enable or disable nonblocking mode on socket s. lpvInBuffer points at an unsigned long, which is nonzero if nonblocking mode is to be enabled and zero if it is to be disabled. When a socket is created, it operates in blocking mode (that is, nonblocking mode is disabled). This is consistent with BSD sockets.

The WSAAsyncSelect or WSAEventSelect routine automatically sets a socket to nonblocking mode. If WSAAsyncSelect or WSAEventSelect has been issued on a socket, then any attempt to use WSAIoctl to set the socket back to blocking mode will fail with WSAEINVAL. To set the socket back to blocking mode, an application must first disable WSAAsyncSelect by calling WSAAsyncSelect with the lEvent parameter equal to zero, or disable WSAEventSelect by calling WSAEventSelect with the lNetworkEvents parameter equal to zero.

FIONREAD

Determine the amount of data which can be read atomically from socket s. lpvOutBuffer points at an unsigned long in which WSAIoctl stores the result. If s is stream oriented (for example, type SOCK_STREAM), FIONREAD returns the total amount of data which may be read in a single receive operation; this is normally the same as the total amount of data queued on the socket. If s is message oriented (for example, type SOCK_DGRAM), FIONREAD returns the size of the first datagram (message) queued on the socket.

SIOCATMARK

Determine whether or not all out-of-band data has been read. This applies only to a socket of stream style (for example, type SOCK_STREAM) which has been configured for in-line reception of any out-of-band data (SO_OOBINLINE). If no out-of-band data is waiting to be read, the operation returns TRUE. Otherwise, it returns FALSE, and the next receive operation performed on the socket will retrieve some or all of the data preceding the "mark"; the application should use the SIOCATMARK operation to determine whether any remains. If there is any normal data preceding the "urgent" (out of band) data, it will be received in order. (Note that receive operations will never mix out-of-band and normal data in the same call.) lpvOutBuffer points at a BOOL in which WSAIoctl stores the result.

The following Windows Sockets 2 commands are supported:

Parameters

SIO_ASSOCIATE_HANDLE (opcode setting: I, T==1)

Associate this socket with the specified handle of a companion interface. The input buffer contains the integer value corresponding to the manifest constant for the companion interface (for example, TH_NETDEV and TH_TAPI.), followed by a value which is a handle of the specified companion interface, along with any other required information. Refer to the appropriate section in the Windows Sockets 2 Protocol-Specific Annex for details specific to a particular companion interface. The total size is reflected in the input buffer length. No output buffer is required. The WSAENOPROTOOPT error code is indicated for service providers which do not support this ioctl.

SIO_ENABLE_CIRCULAR_QUEUEING (opcode setting: V, T==1)

Indicates to the underlying message-oriented service provider that a newly arrived message should never be dropped because of a buffer queue overflow. Instead, the oldest message in the queue should be eliminated in order to accommodate the newly arrived message. No input and output buffers are required. Note that this ioctl is only valid for sockets associated with unreliable, message-oriented protocols. The WSAENOPROTOOPT error code is indicated for service providers which do not support this ioctl.

SIO_FIND_ROUTE (opcode setting: O, T==1)

When issued, this ioctl requests that the route to the remote address specified as a sockaddr in the input buffer be discovered. If the address already exists in the local cache, its entry is invalidated. In the case of Novell's IPX, this call initiates an IPX GetLocalTarget (GLT), which queries the network for the given remote address.

SIO_FLUSH (opcode setting: V, T==1)

Discards current contents of the sending queue associated with this socket. No input and output buffers are required. The WSAENOPROTOOPT error code is indicated for service providers which do not support this ioctl.

SIO_GET_BROADCAST_ADDRESS (opcode setting: O, T==1)

This ioctl fills the output buffer with a sockaddr structure containing a suitable broadcast address for use with sendto/WSASendTo.

SIO_GET_EXTENSION_FUNCTION_POINTER (opcode setting: O, I, T==1)

Retrieve a pointer to the specified extension function supported by the associated service provider. The input buffer contains a globally unique identifier (GUID) whose value identifies the extension function in question. The pointer to the desired function is returned in the output buffer. Extension function identifiers are established by service provider vendors and should be included in vendor documentation that describes extension function capabilities and semantics.

SIO_GET_QOS (opcode setting: O, T==1)

Retrieve the QOS structure associated with the socket. The input buffer is optional. Some protocols (for example, RSVP) allow the input buffer to be used to qualify a QOS request. The QOS structure will be copied into the output buffer. The output buffer must be sized large enough to be able to contain the full QOS structure. The WSAENOPROTOOPT error code is indicated for service providers which do not support QOS.

SIO_GET_GROUP_QOS (opcode setting: O, I, T==1)

Retrieve the QOS structure associated with the socket group to which this socket belongs. The input buffer is optional. Some protocols (for example, RSVP) allow the input buffer to be used to qualify a QOS request. The QOS structure will be copied into the output buffer. If this socket does not belong to an appropriate socket group, the SendingFlowspec and ReceivingFlowspec fields of the returned QOS structure are set to NULL. The WSAENOPROTOOPT error code is indicated for service providers which do not support QOS.

SIO_MULTIPOINT_LOOPBACK (opcode setting: I, T==1)

Controls whether data sent in a multipoint session will also be received by the same socket on the local host. A value of TRUE causes loopback reception to occur while a value of FALSE prohibits this.

SIO_MULTICAST_SCOPE (opcode setting: I, T==1)

Specifies the scope over which multicast transmissions will occur. Scope is defined as the number of routed network segments to be covered. A scope of zero would indicate that the multicast transmission would not be placed "on the wire" but could be disseminated across sockets within the local host. A scope value of one (the default) indicates that the transmission will be placed on the wire, but will not cross any routers. Higher scope values determine the number of routers that may be crossed. Note that this corresponds to the time-to-live (TTL) parameter in IP multicasting.

SIO_SET_QOS (opcode setting: I, T==1)

Associate the supplied QOS structure with the socket. No output buffer is required, the QOS structure will be obtained from the input buffer. The WSAENOPROTOOPT error code is indicated for service providers which do not support QOS.

SIO_SET_GROUP_QOS (opcode setting: I, T==1)

Establish the supplied QOS structure with the socket group to which this socket belongs. No output buffer is required, the QOS structure will be obtained from the input buffer. The WSAENOPROTOOPT error code is indicated for service providers which do not support QOS, or if the socket descriptor specified is not the creator of the associated socket group.

SIO_TRANSLATE_HANDLE (opcode setting: I, O, T==1)

To obtain a corresponding handle for socket s that is valid in the context of a companion interface (for example, TH_NETDEV and TH_TAPI). A manifest constant identifying the companion interface along with any other needed parameters are specified in the input buffer. The corresponding handle will be available in the output buffer upon completion of this function. Refer to the appropriate section in the Windows Sockets 2 Protocol-Specific Annex for details specific to a particular companion interface. The WSAENOPROTOOPT error code is indicated for service providers which do not support this ioctl for the specified companion interface.

If an overlapped operation completes immediately, this function returns a value of zero and the lpcbBytesReturned parameter is updated with the number of bytes in the output buffer. If the overlapped operation is successfully initiated and will complete later, this function returns SOCKET_ERROR and indicates error code WSA_IO_PENDING. In this case, lpcbBytesReturned is not updated. When the overlapped operation completes the amount of data in the output buffer is indicated either through the cbTransferred parameter in the completion routine (if specified), or through the lpcbTransfer parameter in WSAGetOverlappedResult.

When called with an overlapped socket, the lpOverlapped parameter must be valid for the duration of the overlapped operation. The WSAOVERLAPPED structure has the following form:

typedef struct _WSAOVERLAPPED {

DWORD Internal; // reserved

DWORD InternalHigh; // reserved

DWORD Offset; // reserved

DWORD OffsetHigh; // reserved

WSAEVENT hEvent;

} WSAOVERLAPPED, FAR * LPWSAOVERLAPPED;

If the lpCompletionRoutine parameter is NULL, the hEvent field of lpOverlapped is signaled when the overlapped operation completes if it contains a valid event object handle. An application can use WSAWaitForMultipleEvents or WSAGetOverlappedResult to wait or poll on the event object.

If lpCompletionRoutine is not NULL, the hEvent field is ignored and can be used by the application to pass context information to the completion routine.

The prototype of the completion routine is as follows:

  • oid CALLBACK CompletionRoutine(
    IN DWORD
    dwError,
    IN DWORD
    cbTransferred,
    IN LPWSAOVERLAPPED
    lpOverlapped,
    IN DWORD
    dwFlags
    );

CompletionRoutine is a placeholder for an application-defined or library-defined function. dwError specifies the completion status for the overlapped operation as indicated by lpOverlapped. cbTransferred specifies the number of bytes returned. Currently there are no flag values defined and dwFlags will be zero. This function does not return a value.

Returning from this function allows invocation of another pending completion routine for this socket. The completion routines may be called in any order, not necessarily in the same order the overlapped operations are completed.

Compatibility

The ioctl codes with T == 0 are a subset of the ioctl codes used in Berkeley sockets. In particular, there is no command which is equivalent to FIOASYNC.

Return Values

Upon successful completion, the WSAIoctl returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code may be retrieved by calling WSAGetLastError.

Error Codes

WSAENETDOWN
The network subsystem has failed.
WSAEFAULT
The lpvInBuffer, lpvOutBuffer or lpcbBytesReturned argument is not totally contained in a valid part of the user address space, or the cbInBuffer or cbOutBuffer argument is too small.
WSAEINVAL
dwIoControlCode is not a valid command, or a supplied input parameter is not acceptable, or the command is not applicable to the type of socket supplied.
WSAEINPROGRESS
The function is invoked when a callback is in progress.
WSAENOTSOCK
The descriptor s is not a socket.
WSAEOPNOTSUPP
The specified ioctl command cannot be realized. (For examle, the flow specifications specified in SIO_SET_QOS or SIO_SET_GROUP_QOS cannot be satisfied.)
WSA_IO_PENDING
An overlapped operation was successfully initiated and completion will be indicated at a later time.
WSAEWOULDBLOCK
The socket is marked as nonblocking and the requested operation would block.

See Also

getsockopt
, ioctlsocket, setsockopt, socket, WSASocket


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