Name
ddp — Linux AppleTalk protocol implementation
DESCRIPTION
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.
Address Format
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.
Socket Options
No protocol-specific socket options are supported.
Sysctls
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.
Ioctls
All ioctls described in socket(7) apply to
ddp.
ERRORS
- 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.
VERSIONS
Appletalk is supported by Linux 2.0 or higher. The
sysctl interface is new in
Linux 2.2.
NOTES
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.
Compatibility
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.
BUGS
There are too many inconsistent error values.
The ioctls used to configure routing tables, devices, AARP
tables and other devices are not yet described.
SEE ALSO
recvmsg(2), sendmsg(2), capabilities(7), socket(7)
This man page is Copyright (C) 1998 Alan Cox.
Permission is granted to distribute possibly modified copies
of this page provided the header is included verbatim,
and in case of nontrivial modification author and date
of the modification is added to the header.
$Id: ddp.7,v 1.3 1999/05/13 11:33:22 freitag Exp $
|
