ddp — Linux AppleTalk protocol implementation
#include <sys/socket.h> #include <netatalk/at.h> ddp_socket = socket(PF_APPLETALK, SOCK_DGRAM, 0); raw_socket = socket(PF_APPLETALK, SOCK_RAW, protocol);
Linux implements the Appletalk protocols described in
Inside Appletalk. Only
the DDP layer and AARP are present in the kernel. They are
designed to be used via the netatalk protocol libraries.
This page documents the interface for those who wish or need
to use the DDP layer directly.
The communication between Appletalk and the user program works using a BSD-compatible socket interface. For more information on sockets, see socket(7).
An AppleTalk socket is created by calling the socket(2) function with a
PF_APPLETALK socket family
argument. Valid socket types are SOCK_DGRAM to open a ddp socket or SOCK_RAW to open a raw socket. protocol is the Appletalk
protocol to be received or sent. For SOCK_RAW you must specify ATPROTO_DDP.
Raw sockets may be only opened by a process with effective
user ID 0 or when the process has the CAP_NET_RAW capability.
An Appletalk socket address is defined as a combination of a network number, a node number, and a port number.
struct at_addr { u_short s_net;u_char s_node;}; struct sockaddr_atalk { sa_family_t sat_family;/* address family */ u_char sat_port;/* port */ struct at_addr sat_addr;/* net/node */ };
sat_family is
always set to AF_APPLETALK.
sat_port contains
the port. The port numbers below 129 are known as
reserved ports. Only
processes with the effective user ID 0 or the CAP_NET_BIND_SERVICE capability may
bind(2) to these sockets.
sat_addr is the
host address. The net member of struct at_addr contains the host
network in network byte order. The value of AT_ANYNET is a wildcard and also implies
“this network”. The
node member of
struct at_addr
contains the host node number. The value of AT_ANYNODE is a wildcard and also implies
“this node”. The
value of ATADDR_BCAST is a
link local broadcast address.
IP supports a sysctl interface to configure some global
AppleTalk parameters. The sysctls can be accessed by
reading or writing the /proc/sys/net/atalk/* files or with the
sysctl(2) interface.
The time interval (in seconds) before an AARP cache entry expires.
The time interval (in seconds) before an AARP cache entry is resolved.
The number of retransmissions of an AARP query before the node is declared dead.
The timer rate (in seconds) for the timer driving AARP.
The default values match the specification and should never need to be changed.
The operation is only defined on a connected socket, but the socket wasn't connected.
Invalid argument passed.
Datagram is bigger than the DDP MTU.
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 CAP_NET_BIND_SERVICE.
Tried to bind to an address already in use.
Not enough memory available.
Invalid socket option passed.
User doesn't have permission to set high priority, make a configuration change, or send signals to the requested process or group,
A non-existent interface was requested or the requested source address was not local.
Operation on a nonblocking socket would block.
The socket was unconfigured, or an unknown socket type was requested.
connect(2) was called on an already connected socket.
A connection operation on a non-blocking socket is already in progress.
A connection was closed during an accept(2).
The connection was unexpectedly closed or shut down by the other end.
SIOCGSTAMP was called
on a socket where no packet arrived.
No routing table entry matches the destination address.
Network device not available or not capable of sending IP.
A kernel subsystem was not configured.
Be very careful with the SO_BROADCAST option − it is not
privileged in Linux. It is easy to overload the network with
careless sending to broadcast addresses.
The basic AppleTalk socket interface is compatible with
netatalk on
BSD-derived systems. Many BSD systems fail to check
SO_BROADCAST when sending
broadcast frames; this can lead to compatibility
problems.
The raw socket mode is unique to Linux and exists to support the alternative CAP package and AppleTalk monitoring tools more easily.
There are too many inconsistent error values.
The ioctls used to configure routing tables, devices, AARP tables and other devices are not yet described.
recvmsg(2), sendmsg(2), capabilities(7), socket(7)
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