Originální popis anglicky:
ddp - Linux AppleTalk protocol implementation
Návod, kniha: Linux Programmer's Manual
#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.
No protocol-specific socket options are supported.
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.
- aarp-expiry-time
- The time interval (in seconds) before an AARP cache entry
expires.
- aarp-resolve-time
- The time interval (in seconds) before an AARP cache entry
is resolved.
- aarp-retransmit-limit
- The number of retransmissions of an AARP query before the
node is declared dead.
- aarp-tick-time
- The timer rate (in seconds) for the timer driving
AARP.
The default values match the specification and should never need to be changed.
All ioctls described in
socket(7) apply to ddp.
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.
Appletalk is supported by Linux 2.0 or higher. The
sysctl interface is
new in Linux 2.2.
- ENOTCONN
- The operation is only defined on a connected socket, but
the socket wasn't connected.
- EINVAL
- Invalid argument passed.
- EMSGSIZE
- Datagram is bigger than the DDP MTU.
- 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 CAP_NET_BIND_SERVICE.
- EADDRINUSE
- Tried to bind to an address already in use.
- ENOMEM and ENOBUFS
- Not enough memory available.
- ENOPROTOOPT and EOPNOTSUPP
- Invalid socket option passed.
- EPERM
- User doesn't have permission to set high priority, make a
configuration change, or send signals to the requested process or
group,
- EADDRNOTAVAIL
- A non-existent interface was requested or the requested
source address was not local.
- EAGAIN
- Operation on a nonblocking socket would block.
- ESOCKTNOSUPPORT
- The socket was unconfigured, or an unknown socket type was
requested.
- EISCONN
- connect(2) was called on an already connected
socket.
- EALREADY
- A connection operation on a non-blocking socket is already
in progress.
- ECONNABORTED
- A connection was closed during an accept(2).
- EPIPE
- The connection was unexpectedly closed or shut down by the
other end.
- ENOENT
- SIOCGSTAMP was called on a socket where no packet
arrived.
- EHOSTUNREACH
- No routing table entry matches the destination
address.
- ENODEV
- Network device not available or not capable of sending
IP.
- ENOPKG
- A kernel subsystem was not configured.
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)
