xnu-3247.1.106.tar.gz

[apple/xnu.git] / bsd / sys / kpi_socketfilter.h

/*
 * Copyright (c) 2008 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
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 */
/*!
        @header kpi_socketfilter.h
        This header defines an API for intercepting communications at the
        socket layer.

        For the most part, socket filters want to do three things: Filter
        data in and out, watch for state changes, and intercept a few calls
        for security. The number of function pointers supplied by a socket
        filter has been significantly reduced. The filter no longer has any
        knowledge of socket buffers. The filter no longer intercepts nearly
        every internal socket call. There are two data filters, an in
        filter, and an out filter. The in filter occurs before data is
        placed in the receive socket buffer. This is done to avoid waking
        the process unnecessarily. The out filter occurs before the data is
        appended to the send socket buffer. This should cover inbound and
        outbound data. For monitoring state changes, we've added a notify
        function that will be called when various events that the filter can
        not intercept occur. In addition, we've added a few functions that a
        filter may use to intercept common operations. These functions are:
        connect (inbound), connect (outbound), bind, set socket option,
        get socket option, and listen. Bind, listen, connect in, and connect
        out could be used together to build a fairly comprehensive firewall
        without having to do much with individual packets.
 */
#ifndef __KPI_SOCKETFILTER__
#define __KPI_SOCKETFILTER__

#include <sys/kernel_types.h>
#include <sys/kpi_socket.h>

struct sockaddr;

/*!
        @enum sflt_flags
        @abstract Constants defining mbuf flags. Only the flags listed below
                can be set or retrieved.
        @constant SFLT_GLOBAL Indicates this socket filter should be
                attached to all new sockets when they're created.
        @constant SFLT_PROG Indicates this socket filter should be attached
                only when request by the application using the SO_NKE socket
                option.
        @constant SFLT_EXTENDED Indicates that this socket filter utilizes
                the extended fields within the sflt_filter structure.
        @constant SFLT_EXTENDED_REGISTRY Indicates that this socket filter
                wants to attach to all the sockets already present on the
                system. It will also receive notifications for these sockets.
*/
enum {
        SFLT_GLOBAL             = 0x01,
        SFLT_PROG               = 0x02,
        SFLT_EXTENDED           = 0x04,
        SFLT_EXTENDED_REGISTRY  = 0x08
};
typedef u_int32_t       sflt_flags;

/*!
        @typedef sflt_handle
        @abstract A 4 byte identifier used with the SO_NKE socket option to
                identify the socket filter to be attached.
*/
typedef u_int32_t       sflt_handle;

/*!
        @enum sflt_event_t
        @abstract Events notify a filter of state changes and other various
                events related to the socket. These events cannot be prevented
                or intercepted, only observed.
        @constant sock_evt_connected Indicates this socket has moved to the
                connected state.
        @constant sock_evt_disconnected Indicates this socket has moved to
                the disconnected state.
        @constant sock_evt_flush_read The read socket buffer has been
                flushed.
        @constant sock_evt_shutdown The read and or write side(s) of the
                connection have been shutdown. The param will point to an
                integer that indicates the direction that has been shutdown. See
                'man 2 shutdown' for more information.
        @constant sock_evt_cantrecvmore Indicates the socket cannot receive
                more data.
        @constant sock_evt_cantsendmore Indicates the socket cannot send
                more data.
        @constant sock_evt_closing Indicates the socket is closing.
        @constant sock_evt_bound Indicates this socket has moved to the
                bound state (only for PF_INET/PF_INET6 domain).
*/
enum {
        sock_evt_connecting             = 1,
        sock_evt_connected              = 2,
        sock_evt_disconnecting          = 3,
        sock_evt_disconnected           = 4,
        sock_evt_flush_read             = 5,
        sock_evt_shutdown               = 6, /* param points to an integer specifying how (read, write, or both) see man 2 shutdown */
        sock_evt_cantrecvmore           = 7,
        sock_evt_cantsendmore           = 8,
        sock_evt_closing                = 9,
        sock_evt_bound                  = 10
};
typedef u_int32_t       sflt_event_t;

/*!
        @enum sflt_data_flag_t
        @abstract Inbound and outbound data filters may handle many
                different types of incoming and outgoing data. These flags help
                distinguish between normal data, out-of-band data, and records.
        @constant sock_data_filt_flag_oob Indicates this data is out-of-band
                data.
        @constant sock_data_filt_flag_record Indicates this data is a
                record. This flag is only ever seen on inbound data.
*/
enum {
        sock_data_filt_flag_oob         = 1,
        sock_data_filt_flag_record      = 2
};
typedef u_int32_t       sflt_data_flag_t;

__BEGIN_DECLS

/*!
        @typedef sf_unregistered_func

        @discussion sf_unregistered_func is called to notify the filter it
                has been unregistered. This is the last function the stack will
                call and this function will only be called once all other
                function calls in to your filter have completed. Once this
                function has been called, your kext may safely unload.
        @param handle The socket filter handle used to identify this filter.
*/
typedef void (*sf_unregistered_func)(sflt_handle handle);

/*!
        @typedef sf_attach_func

        @discussion sf_attach_func is called to notify the filter it has
                been attached to a socket. The filter may allocate memory for
                this attachment and use the cookie to track it. This filter is
                called in one of two cases:
                1) You've installed a global filter and a new socket was created.
                2) Your non-global socket filter is being attached using the SO_NKE
                socket option.
        @param cookie Used to allow the socket filter to set the cookie for
                this attachment.
        @param so The socket the filter is being attached to.
        @result If you return a non-zero value, your filter will not be
                attached to this socket.
*/
typedef errno_t (*sf_attach_func)(void  **cookie, socket_t so);

/*!
        @typedef sf_detach_func

        @discussion sf_detach_func is called to notify the filter it has
                been detached from a socket. If the filter allocated any memory
                for this attachment, it should be freed. This function will
                be called when the socket is disposed of.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @result If you return a non-zero value, your filter will not be
                attached to this socket.
*/
typedef void (*sf_detach_func)(void *cookie, socket_t so);

/*!
        @typedef sf_notify_func

        @discussion sf_notify_func is called to notify the filter of various
                state changes and other events occuring on the socket.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param event The type of event that has occurred.
        @param param Additional information about the event.
*/
typedef void (*sf_notify_func)(void *cookie, socket_t so, sflt_event_t event,
    void *param);

/*!
        @typedef sf_getpeername_func

        @discussion sf_getpeername_func is called to allow a filter to
                to intercept the getpeername function. When called, sa will
                point to a pointer to a socket address that was malloced
                in zone M_SONAME. If you want to replace this address, either
                modify the currenty copy or allocate a new one and free the
                old one.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param sa A pointer to a socket address pointer.
        @result If you return a non-zero value, processing will stop. If
                you return EJUSTRETURN, no further filters will be called
                but a result of zero will be returned to the caller of
                getpeername.
*/
typedef int (*sf_getpeername_func)(void *cookie, socket_t so,
    struct sockaddr **sa);

/*!
        @typedef sf_getsockname_func

        @discussion sf_getsockname_func is called to allow a filter to
                to intercept the getsockname function. When called, sa will
                point to a pointer to a socket address that was malloced
                in zone M_SONAME. If you want to replace this address, either
                modify the currenty copy or allocate a new one and free the
                old one.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param sa A pointer to a socket address pointer.
        @result If you return a non-zero value, processing will stop. If
                you return EJUSTRETURN, no further filters will be called
                but a result of zero will be returned to the caller of
                getsockname.
*/
typedef int (*sf_getsockname_func)(void *cookie, socket_t so,
    struct sockaddr **sa);

/*!
        @typedef sf_data_in_func

        @discussion sf_data_in_func is called to filter incoming data. If your
                filter intercepts data for later reinjection, it must queue
                all incoming data to preserve the order of the data. Use
                sock_inject_data_in to later reinject this data if you return
                EJUSTRETURN. Warning: This filter is on the data path. Do not
                spend excesive time. Do not wait for data on another socket.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param from The addres the data is from, may be NULL if the socket
                is connected.
        @param data The data being received. Control data may appear in the
                mbuf chain, be sure to check the mbuf types to find control
                data.
        @param control Control data being passed separately from the data.
        @param flags Flags to indicate if this is out of band data or a
                record.
        @result Return:
                0 - The caller will continue with normal processing of the data.
                EJUSTRETURN - The caller will stop processing the data, the
                        data will not be freed.
                Anything Else - The caller will free the data and stop
                        processing.
*/
typedef errno_t (*sf_data_in_func)(void *cookie, socket_t so,
    const struct sockaddr *from, mbuf_t *data, mbuf_t *control,
    sflt_data_flag_t flags);

/*!
        @typedef sf_data_out_func

        @discussion sf_data_out_func is called to filter outbound data. If
                your filter intercepts data for later reinjection, it must queue
                all outbound data to preserve the order of the data when
                reinjecting. Use sock_inject_data_out to later reinject this
                data.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param from The address the data is from, may be NULL if the socket
                is connected.
        @param data The data being received. Control data may appear in the
                mbuf chain, be sure to check the mbuf types to find control
                data.
        @param control Control data being passed separately from the data.
        @param flags Flags to indicate if this is out of band data or a
                record.
        @result Return:
                0 - The caller will continue with normal processing of the data.
                EJUSTRETURN - The caller will stop processing the data,
                        the data will not be freed.
                Anything Else - The caller will free the data and stop
                        processing.
*/
typedef errno_t (*sf_data_out_func)(void *cookie, socket_t so,
    const struct sockaddr *to, mbuf_t *data, mbuf_t *control,
    sflt_data_flag_t flags);

/*!
        @typedef sf_connect_in_func

        @discussion sf_connect_in_func is called to filter inbound connections.
                A protocol will call this before accepting an incoming
                connection and placing it on the queue of completed connections.
                Warning: This filter is on the data path. Do not spend excesive
                time. Do not wait for data on another socket.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param from The address the incoming connection is from.
        @result Return:
                0 - The caller will continue with normal processing of the
                        connection.
                Anything Else - The caller will rejecting the incoming
                        connection.
*/
typedef errno_t (*sf_connect_in_func)(void *cookie, socket_t so,
    const struct sockaddr *from);

/*!
        @typedef sf_connect_out_func

        @discussion sf_connect_out_func is called to filter outbound
                connections. A protocol will call this before initiating an
                outbound connection.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param to The remote address of the outbound connection.
        @result Return:
                0 - The caller will continue with normal processing of the
                        connection.
                EJUSTRETURN - The caller will return with a value of 0 (no error)
                        from that point without further processing the connect command. The
                        protocol layer will not see the call.
                Anything Else - The caller will rejecting the outbound
                        connection.
*/
typedef errno_t (*sf_connect_out_func)(void *cookie, socket_t so,
    const struct sockaddr *to);

/*!
        @typedef sf_bind_func

        @discussion sf_bind_func is called before performing a bind
                operation on a socket.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param to The local address of the socket will be bound to.
        @result Return:
                0 - The caller will continue with normal processing of the bind.
                EJUSTRETURN - The caller will return with a value of 0 (no error)
                        from that point without further processing the bind command. The
                        protocol layer will not see the call.
                Anything Else - The caller will rejecting the bind.
*/
typedef errno_t (*sf_bind_func)(void *cookie, socket_t so,
    const struct sockaddr *to);

/*!
        @typedef sf_setoption_func

        @discussion sf_setoption_func is called before performing setsockopt
                on a socket.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param opt The socket option to set.
        @result Return:
                0 - The caller will continue with normal processing of the
                        setsockopt.
                EJUSTRETURN - The caller will return with a value of 0 (no error)
                        from that point without further propagating the set option
                        command. The socket and protocol layers will not see the call.
                Anything Else - The caller will stop processing and return
                        this error.
*/
typedef errno_t (*sf_setoption_func)(void *cookie, socket_t so, sockopt_t opt);

/*!
        @typedef sf_getoption_func

        @discussion sf_getoption_func is called before performing getsockopt
                on a socket.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param opt The socket option to get.
        @result Return:
                0 - The caller will continue with normal processing of the
                        getsockopt.
                EJUSTRETURN - The caller will return with a value of 0 (no error)
                        from that point without further propagating the get option
                        command. The socket and protocol layers will not see the call.
                Anything Else - The caller will stop processing and return
                        this error.
*/
typedef errno_t (*sf_getoption_func)(void *cookie, socket_t so, sockopt_t opt);

/*!
        @typedef sf_listen_func

        @discussion sf_listen_func is called before performing listen
                on a socket.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @result Return:
                0 - The caller will continue with normal processing of listen.
                EJUSTRETURN - The caller will return with a value of 0 (no error)
                from that point without further processing the listen command. The
                protocol will not see the call.
                Anything Else - The caller will stop processing and return
                        this error.
*/
typedef errno_t (*sf_listen_func)(void *cookie, socket_t so);

/*!
        @typedef sf_ioctl_func

        @discussion sf_ioctl_func is called before performing an ioctl
                on a socket.

                All undefined ioctls are reserved for future use by Apple. If
                you need to communicate with your kext using an ioctl, please
                use SIOCSIFKPI and SIOCGIFKPI.
        @param cookie Cookie value specified when the filter attach was
                called.
        @param so The socket the filter is attached to.
        @param request The ioctl name.
        @param argp A pointer to the ioctl parameter.
        @result Return:
                0 - The caller will continue with normal processing of
                        this ioctl.
                EJUSTRETURN - The caller will return with a value of 0 (no error)
                        from that point without further processing or propogating
                        the ioctl.
                Anything Else - The caller will stop processing and return
                        this error.
*/
typedef errno_t (*sf_ioctl_func)(void *cookie, socket_t so,
    unsigned long request, const char* argp);

/*!
        @typedef sf_accept_func

        @discussion sf_accept_func is called after a socket is dequeued
                off the completed (incoming) connection list and before
                the file descriptor is associated with it.  A filter can
                utilize this callback to intercept the accepted socket
                in order to examine it, prior to returning the socket to
                the caller of accept.  Such a filter may also choose to
                discard the accepted socket if it wishes to do so.
        @param cookie Cookie value specified when the filter attach was called.
        @param so_listen The listening socket.
        @param so The socket that is about to be accepted.
        @param local The local address of the about to be accepted socket.
        @param remote The remote address of the about to be accepted socket.
        @result Return:
                0 - The caller will continue with normal processing of accept.
                EJUSTRETURN - The to be accepted socket will be disconnected
                    prior to being returned to the caller of accept.  No further
                    control or data operations on the socket will be allowed.
                    This is the recommended return value as it has the least
                    amount of impact, especially to applications which don't
                    check the error value returned by accept.
                Anything Else - The to be accepted socket will be closed and
                    the error will be returned to the caller of accept.
                    Note that socket filter developers are advised to exercise
                    caution when returning non-zero values to the caller,
                    since some applications don't check the error value
                    returned by accept and therefore risk breakage.
 */
typedef errno_t (*sf_accept_func)(void *cookie, socket_t so_listen, socket_t so,
    const struct sockaddr *local, const struct sockaddr *remote);

/*!
        @struct sflt_filter
        @discussion This structure is used to define a socket filter.
        @field sf_handle A value used to find socket filters by
                applications. An application can use this value to specify that
                this filter should be attached when using the SO_NKE socket
                option.
        @field sf_flags Indicate whether this filter should be attached to
                all new sockets or just those that request the filter be
                attached using the SO_NKE socket option. If this filter
                utilizes the socket filter extension fields, it must also
                set SFLT_EXTENDED.
        @field sf_name A name used for debug purposes.
        @field sf_unregistered Your function for being notified when your
                filter has been unregistered.
        @field sf_attach Your function for handling attaches to sockets.
        @field sf_detach Your function for handling detaches from sockets.
        @field sf_notify Your function for handling events. May be null.
        @field sf_data_in Your function for handling incoming data. May be
                null.
        @field sf_data_out Your function for handling outgoing data. May be
                null.
        @field sf_connect_in Your function for handling inbound
                connections. May be null.
        @field sf_connect_out Your function for handling outbound
                connections. May be null.
        @field sf_bind Your function for handling binds. May be null.
        @field sf_setoption Your function for handling setsockopt. May be null.
        @field sf_getoption Your function for handling getsockopt. May be null.
        @field sf_listen Your function for handling listen. May be null.
        @field sf_ioctl Your function for handling ioctls. May be null.
        @field sf_len Length of socket filter extension structure; developers
                must initialize this to sizeof sflt_filter_ext structure.
                This field and all fields following it will only be valid
                if SFLT_EXTENDED flag is set in sf_flags field.
        @field sf_ext_accept Your function for handling inbound connections
                at accept time.  May be null.
        @field sf_ext_rsvd Reserved for future use; you must initialize
                the reserved fields with zeroes.
*/
struct sflt_filter {
        sflt_handle                     sf_handle;
        int                             sf_flags;
        char                            *sf_name;

        sf_unregistered_func            sf_unregistered;
        sf_attach_func                  sf_attach;
        sf_detach_func                  sf_detach;

        sf_notify_func                  sf_notify;
        sf_getpeername_func             sf_getpeername;
        sf_getsockname_func             sf_getsockname;
        sf_data_in_func                 sf_data_in;
        sf_data_out_func                sf_data_out;
        sf_connect_in_func              sf_connect_in;
        sf_connect_out_func             sf_connect_out;
        sf_bind_func                    sf_bind;
        sf_setoption_func               sf_setoption;
        sf_getoption_func               sf_getoption;
        sf_listen_func                  sf_listen;
        sf_ioctl_func                   sf_ioctl;
        /*
         * The following are valid only if SFLT_EXTENDED flag is set.
         * Initialize sf_ext_len to sizeof sflt_filter_ext structure.
         * Filters must also initialize reserved fields with zeroes.
         */
        struct sflt_filter_ext {
                unsigned int            sf_ext_len;
                sf_accept_func          sf_ext_accept;
                void                    *sf_ext_rsvd[5];        /* Reserved */
        } sf_ext;
#define sf_len          sf_ext.sf_ext_len
#define sf_accept       sf_ext.sf_ext_accept
};

/*!
        @function sflt_register
        @discussion Registers a socket filter. See 'man 2 socket' for a
                desciption of domain, type, and protocol.
        @param filter A structure describing the filter.
        @param domain The protocol domain these filters will be attached to.
                Only PF_INET & PF_INET6 domains are supported.
        @param type The socket type these filters will be attached to.
        @param protocol The protocol these filters will be attached to.
        @result 0 on success otherwise the errno error.
 */
extern errno_t sflt_register(const struct sflt_filter *filter, int domain,
    int type, int protocol);

/*!
        @function sflt_unregister
        @discussion Unregisters a socket filter. This will not detach the
                socket filter from all sockets it may be attached to at the
                time, it will just prevent the socket filter from being attached
                to any new sockets.
        @param handle The sf_handle of the socket filter to unregister.
        @result 0 on success otherwise the errno error.
 */
extern errno_t sflt_unregister(sflt_handle handle);

/*!
        @function sflt_attach
        @discussion Attaches a socket filter to the specified socket. A
                filter must be registered before it can be attached.
        @param socket The socket the filter should be attached to.
        @param handle The handle of the registered filter to be attached.
        @result 0 on success otherwise the errno error.
 */
extern errno_t sflt_attach(socket_t so, sflt_handle);

/*!
        @function sflt_detach
        @discussion Detaches a socket filter from a specified socket.
        @param socket The socket the filter should be detached from.
        @param handle The handle of the registered filter to be detached.
        @result 0 on success otherwise the errno error.
 */
extern errno_t sflt_detach(socket_t so, sflt_handle);

/* Functions for manipulating sockets */
/*
 * Inject data in to the receive buffer of the socket as if it
 * had come from the network.
 *
 * flags should match sflt_data_flag_t
 */

/*!
        @function sock_inject_data_in
        @discussion Inject data in to the receive buffer of the socket as if
                it had come from the network.
        @param so The socket to inject the data on.
        @param from The address the data is from, only necessary on
                un-connected sockets. A copy of the address will be made, caller
                is responsible for freeing the address after calling this
                function.
        @param data The data and possibly control mbufs.
        @param control The separate control mbufs.
        @param flags Flags indicating the type of data.
        @result 0 on success otherwise the errno error. If the function
                returns an error, the caller is responsible for freeing the
                mbuf.
 */
extern errno_t sock_inject_data_in(socket_t so, const struct sockaddr *from,
    mbuf_t data, mbuf_t control, sflt_data_flag_t flags);

/*!
        @function sock_inject_data_out
        @discussion Inject data in to the send buffer of the socket as if it
                had come from the client.
        @param so The socket to inject the data on.
        @param to The address the data should be sent to, only necessary on
                un-connected sockets. The caller is responsible for freeing the
                to address after sock_inject_data_out returns.
        @param data The data and possibly control mbufs.
        @param control The separate control mbufs.
        @param flags Flags indicating the type of data.
        @result 0 on success otherwise the errno error. The data and control
                values are always freed regardless of return value.
 */
extern errno_t sock_inject_data_out(socket_t so, const struct sockaddr *to,
    mbuf_t data, mbuf_t control, sflt_data_flag_t flags);


/*
 * sockopt_t accessors
 */

enum {
        sockopt_get     = 1,
        sockopt_set     = 2
};
typedef u_int8_t sockopt_dir;

/*!
        @function sockopt_direction
        @discussion Retrieves the direction of the socket option (Get or
                Set).
        @param sopt The socket option.
        @result sock_opt_get or sock_opt_set.
 */
extern sockopt_dir sockopt_direction(sockopt_t sopt);

/*!
        @function sockopt_level
        @discussion Retrieves the socket option level. (SOL_SOCKET, etc).
        @param sopt The socket option.
        @result The socket option level. See man 2 setsockopt
 */
extern int sockopt_level(sockopt_t sopt);

/*!
        @function sockopt_name
        @discussion Retrieves the socket option name. (SO_SNDBUF, etc).
        @param sopt The socket option.
        @result The socket option name. See man 2 setsockopt
 */
extern int sockopt_name(sockopt_t sopt);

/*!
        @function sockopt_valsize
        @discussion Retrieves the size of the socket option data.
        @param sopt The socket option.
        @result The length, in bytes, of the data.
 */
extern size_t sockopt_valsize(sockopt_t sopt);

/*!
        @function sockopt_copyin
        @discussion Copies the data from the socket option to a buffer.
        @param sopt The socket option.
        @param data A pointer to the buffer to copy the data in to.
        @param length The number of bytes to copy.
        @result An errno error or zero upon success.
 */
extern errno_t sockopt_copyin(sockopt_t sopt, void *data, size_t length);

/*!
        @function sockopt_copyout
        @discussion Copies the data from a buffer to a socket option.
        @param sopt The socket option.
        @param data A pointer to the buffer to copy the data out of.
        @param length The number of bytes to copy.
        @result An errno error or zero upon success.
 */
extern errno_t sockopt_copyout(sockopt_t sopt, void *data, size_t length);

__END_DECLS
#endif /* __KPI_SOCKETFILTER__ */