реализация протокола AppleTalk в Linux (Linux AppleTalk protocol implementation)
Имя (Name)
ddp - Linux AppleTalk protocol implementation
Синопсис (Synopsis)
#include <sys/socket.h>
#include <netatalk/at.h>
ddp_socket = socket(AF_APPLETALK, SOCK_DGRAM, 0);
raw_socket = socket(AF_APPLETALK, SOCK_RAW, protocol);
Описание (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 AF_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 opened only 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 {
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 */
};
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.
/proc interfaces
IP supports a set of /proc interfaces to configure some global
AppleTalk parameters. The parameters can be accessed by reading
or writing files in the directory /proc/sys/net/atalk/.
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.
Ошибки (Error)
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.
EADDRNOTAVAIL
A nonexistent interface was requested or the requested
source address was not local.
EAGAIN Operation on a nonblocking socket would block.
EALREADY
A connection operation on a nonblocking socket is already
in progress.
ECONNABORTED
A connection was closed during an accept(2).
EHOSTUNREACH
No routing table entry matches the destination address.
EINVAL Invalid argument passed.
EISCONN
connect(2) was called on an already connected socket.
EMSGSIZE
Datagram is bigger than the DDP MTU.
ENODEV Network device not available or not capable of sending IP.
ENOENT SIOCGSTAMP was called on a socket where no packet arrived.
ENOMEM and ENOBUFS
Not enough memory available.
ENOPKG A kernel subsystem was not configured.
ENOPROTOOPT and EOPNOTSUPP
Invalid socket option passed.
ENOTCONN
The operation is defined only on a connected socket, but
the socket wasn't connected.
EPERM User doesn't have permission to set high priority, make a
configuration change, or send signals to the requested
process or group.
EPIPE The connection was unexpectedly closed or shut down by the
other end.
ESOCKTNOSUPPORT
The socket was unconfigured, or an unknown socket type was
requested.
Версии (Versions)
AppleTalk is supported by Linux 2.0 or higher. The /proc
interfaces exist since Linux 2.2.
Примечание (Note)
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.
Ошибки (баги) (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.
Смотри также (See also)
recvmsg(2), sendmsg(2), capabilities(7), socket(7)
