.\" This man page is Copyright (C) 1998 Alan Cox.
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" $Id: ddp.7,v 1.3 1999/05/13 11:33:22 freitag Exp $
.\"
.TH ddp 7 2024-05-02 "Linux man-pages (unreleased)"
.SH NAME
ddp \- Linux AppleTalk protocol implementation
.SH SYNOPSIS
.nf
.B #include <sys/socket.h>
.B #include <netatalk/at.h>
.P
.IB ddp_socket " = socket(AF_APPLETALK, SOCK_DGRAM, 0);"
.IB raw_socket " = socket(AF_APPLETALK, SOCK_RAW, " protocol ");"
.fi
.SH DESCRIPTION
Linux implements the AppleTalk protocols described in
.IR "Inside AppleTalk" .
Only the DDP layer and AARP are present in
the kernel.
They are designed to be used via the
.B netatalk
protocol
libraries.
This page documents the interface for those who wish or need to
use the DDP layer directly.
.P
The communication between AppleTalk and the user program works using a
BSD-compatible socket interface.
For more information on sockets, see
.BR socket (7).
.P
An AppleTalk socket is created by calling the
.BR socket (2)
function with a
.B AF_APPLETALK
socket family argument.
Valid socket types are
.B SOCK_DGRAM
to open a
.B ddp
socket or
.B SOCK_RAW
to open a
.B raw
socket.
.I protocol
is the AppleTalk protocol to be received or sent.
For
.B SOCK_RAW
you must specify
.BR ATPROTO_DDP .
.P
Raw sockets may be opened only by a process with effective user ID 0
or when the process has the
.B CAP_NET_RAW
capability.
.SS Address format
An AppleTalk socket address is defined as a combination of a network number,
a node number, and a port number.
.P
.in +4n
.EX
struct at_addr {
    unsigned short s_net;
    unsigned char  s_node;
};
\&
struct sockaddr_atalk {
    sa_family_t    sat_family;    /* address family */
    unsigned char  sat_port;      /* port */
    struct at_addr sat_addr;      /* net/node */
};
.EE
.in
.P
.I sat_family
is always set to
.BR AF_APPLETALK .
.I sat_port
contains the port.
The port numbers below 129 are known as
.IR "reserved ports" .
Only processes with the effective user ID 0 or the
.B CAP_NET_BIND_SERVICE
capability may
.BR bind (2)
to these sockets.
.I sat_addr
is the host address.
The
.I net
member of
.I struct at_addr
contains the host network in network byte order.
The value of
.B AT_ANYNET
is a
wildcard and also implies \[lq]this network.\[rq]
The
.I node
member of
.I struct at_addr
contains the host node number.
The value of
.B AT_ANYNODE
is a
wildcard and also implies \[lq]this node.\[rq] The value of
.B ATADDR_BCAST
is a link
local broadcast address.
.\" FIXME . this doesn't make sense [johnl]
.SS Socket options
No protocol-specific socket options are supported.
.SS /proc interfaces
IP supports a set of
.I /proc
interfaces to configure some global AppleTalk parameters.
The parameters can be accessed by reading or writing files in the directory
.IR /proc/sys/net/atalk/ .
.TP
.I aarp\-expiry\-time
The time interval (in seconds) before an AARP cache entry expires.
.TP
.I aarp\-resolve\-time
The time interval (in seconds) before an AARP cache entry is resolved.
.TP
.I aarp\-retransmit\-limit
The number of retransmissions of an AARP query before the node is declared
dead.
.TP
.I aarp\-tick\-time
The timer rate (in seconds) for the timer driving AARP.
.P
The default values match the specification and should never need to be
changed.
.SS Ioctls
All ioctls described in
.BR socket (7)
apply to DDP.
.\" FIXME . Add a section about multicasting
.SH ERRORS
.TP
.B EACCES
The user tried to execute an operation without the necessary permissions.
These include sending to a broadcast address without
having the broadcast flag set,
and trying to bind to a reserved port without effective user ID 0 or
.BR CAP_NET_BIND_SERVICE .
.TP
.B EADDRINUSE
Tried to bind to an address already in use.
.TP
.B EADDRNOTAVAIL
A nonexistent interface was requested or the requested source address was
not local.
.TP
.B EAGAIN
Operation on a nonblocking socket would block.
.TP
.B EALREADY
A connection operation on a nonblocking socket is already in progress.
.TP
.B ECONNABORTED
A connection was closed during an
.BR accept (2).
.TP
.B EHOSTUNREACH
No routing table entry matches the destination address.
.TP
.B EINVAL
Invalid argument passed.
.TP
.B EISCONN
.BR connect (2)
was called on an already connected socket.
.TP
.B EMSGSIZE
Datagram is bigger than the DDP MTU.
.TP
.B ENODEV
Network device not available or not capable of sending IP.
.TP
.B ENOENT
.B SIOCGSTAMP
was called on a socket where no packet arrived.
.TP
.BR ENOMEM " and " ENOBUFS
Not enough memory available.
.TP
.B ENOPKG
A kernel subsystem was not configured.
.TP
.BR ENOPROTOOPT " and " EOPNOTSUPP
Invalid socket option passed.
.TP
.B ENOTCONN
The operation is defined only on a connected socket, but the socket wasn't
connected.
.TP
.B EPERM
User doesn't have permission to set high priority,
make a configuration change,
or send signals to the requested process or group.
.TP
.B EPIPE
The connection was unexpectedly closed or shut down by the other end.
.TP
.B ESOCKTNOSUPPORT
The socket was unconfigured, or an unknown socket type was requested.
.SH VERSIONS
AppleTalk is supported by Linux 2.0 or higher.
The
.I /proc
interfaces exist since Linux 2.2.
.SH NOTES
Be very careful with the
.B SO_BROADCAST
option; it is not privileged in Linux.
It is easy to overload the network
with careless sending to broadcast addresses.
.SS Compatibility
The basic AppleTalk socket interface is compatible with
.B netatalk
on BSD-derived systems.
Many BSD systems fail to check
.B SO_BROADCAST
when sending broadcast frames; this can lead to compatibility problems.
.P
The
raw
socket mode is unique to Linux and exists to support the alternative CAP
package and AppleTalk monitoring tools more easily.
.SH BUGS
There are too many inconsistent error values.
.P
The ioctls used to configure routing tables, devices,
AARP tables, and other devices are not yet described.
.SH SEE ALSO
.BR recvmsg (2),
.BR sendmsg (2),
.BR capabilities (7),
.BR socket (7)