146 lines
6.2 KiB
Perl
146 lines
6.2 KiB
Perl
.\" Copyright (c) 1983, 1986, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)b.t 8.1 (Berkeley) 6/8/93
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.\"
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.nr H2 1
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.\".ds RH "Raw sockets
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.br
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.ne 2i
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.NH
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\s+2Raw sockets\s0
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.PP
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A raw socket is an object which allows users direct access
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to a lower-level protocol. Raw sockets are intended for knowledgeable
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processes which wish to take advantage of some protocol
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feature not directly accessible through the normal interface, or
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for the development of new protocols built atop existing lower level
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protocols. For example, a new version of TCP might be developed at the
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user level by utilizing a raw IP socket for delivery of packets.
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The raw IP socket interface attempts to provide an identical interface
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to the one a protocol would have if it were resident in the kernel.
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.PP
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The raw socket support is built around a generic raw socket interface,
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(possibly) augmented by protocol-specific processing routines.
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This section will describe the core of the raw socket interface.
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.NH 2
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Control blocks
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.PP
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Every raw socket has a protocol control block of the following form:
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.DS
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.ta \w'struct 'u +\w'caddr_t 'u +\w'sockproto rcb_proto; 'u
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struct rawcb {
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struct rawcb *rcb_next; /* doubly linked list */
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struct rawcb *rcb_prev;
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struct socket *rcb_socket; /* back pointer to socket */
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struct sockaddr rcb_faddr; /* destination address */
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struct sockaddr rcb_laddr; /* socket's address */
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struct sockproto rcb_proto; /* protocol family, protocol */
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caddr_t rcb_pcb; /* protocol specific stuff */
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struct mbuf *rcb_options; /* protocol specific options */
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struct route rcb_route; /* routing information */
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short rcb_flags;
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};
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.DE
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All the control blocks are kept on a doubly linked list for
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performing lookups during packet dispatch. Associations may
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be recorded in the control block and used by the output routine
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in preparing packets for transmission.
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The \fIrcb_proto\fP structure contains the protocol family and protocol
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number with which the raw socket is associated.
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The protocol, family and addresses are
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used to filter packets on input; this will be described in more
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detail shortly. If any protocol-specific information is required,
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it may be attached to the control block using the \fIrcb_pcb\fP
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field.
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Protocol-specific options for transmission in outgoing packets
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may be stored in \fIrcb_options\fP.
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.PP
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A raw socket interface is datagram oriented. That is, each send
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or receive on the socket requires a destination address. This
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address may be supplied by the user or stored in the control block
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and automatically installed in the outgoing packet by the output
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routine. Since it is not possible to determine whether an address
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is present or not in the control block, two flags, RAW_LADDR and
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RAW_FADDR, indicate if a local and foreign address are present.
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Routing is expected to be performed by the underlying protocol
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if necessary.
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.NH 2
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Input processing
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.PP
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Input packets are ``assigned'' to raw sockets based on a simple
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pattern matching scheme. Each network interface or protocol
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gives unassigned packets
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to the raw input routine with the call:
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.DS
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raw_input(m, proto, src, dst)
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struct mbuf *m; struct sockproto *proto, struct sockaddr *src, *dst;
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.DE
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The data packet then has a generic header prepended to it of the
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form
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.DS
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._f
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struct raw_header {
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struct sockproto raw_proto;
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struct sockaddr raw_dst;
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struct sockaddr raw_src;
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};
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.DE
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and it is placed in a packet queue for the ``raw input protocol'' module.
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Packets taken from this queue are copied into any raw sockets that
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match the header according to the following rules,
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.IP 1)
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The protocol family of the socket and header agree.
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.IP 2)
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If the protocol number in the socket is non-zero, then it agrees
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with that found in the packet header.
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.IP 3)
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If a local address is defined for the socket, the address format
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of the local address is the same as the destination address's and
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the two addresses agree bit for bit.
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.IP 4)
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The rules of 3) are applied to the socket's foreign address and the packet's
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source address.
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.LP
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A basic assumption is that addresses present in the
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control block and packet header (as constructed by the network
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interface and any raw input protocol module) are in a canonical
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form which may be ``block compared''.
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.NH 2
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Output processing
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.PP
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On output the raw \fIpr_usrreq\fP routine
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passes the packet and a pointer to the raw control block to the
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raw protocol output routine for any processing required before
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it is delivered to the appropriate network interface. The
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output routine is normally the only code required to implement
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a raw socket interface.
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