ethernet(7)

NAME

Ethernet − raw Ethernet I/O operations

SYNOPSIS

#include <net/rif.h>

DESCRIPTION

Ethernet I/O transactions are typically made by the standard networking software using TCP/IP and related protocols. The interface described below allows programmers to directly access the Ethernet device driver, submitting packets to or receiving packets from the interface without processing by any of the protocol routines.

Raw Ethernet I/O is available on any of the standard Night Hawk Series Ethernet hardware interfaces. Communications can be done on the same interfaces that are used for Internet transactions and at the same time if there is no conflict as to where the received data is to be sent. Access to the raw Ethernet interfaces is restricted to processes having an effective user-id of zero (root).

The raw Ethernet interface supports standard Ethernet message formats, IEEE 802.3 message formats, and IEEE 802.2 Logical Link Control formats. The mode used is selected by the type of open(2) call and through use of ioctl(2) parameters.

DEVICE NAMES

The physical interface to which the process wishes to connect must be specified on the open(2) call. Each interface has two entry points; one for standard raw Ethernet and the other for IEEE 802.2 Logical Link Control formatting. Device names are of the form /dev/xxn and /dev/xxnllc. The xx value is the interface name; it corresponds to the interface name which is displayed when the system is initializing. Standard names are as follows:

     exExcelan
     ieISE daughter card
     egEagle

The n value is the interface number, 0 for the first, 1 for the second, etc. The ’llc’ version of the name is used when IEEE 802.2 LLC formatting is desired.

CONFIGURATION

Special device files needed to utilize raw Ethernet I/O by device name are installed on the system by running the MAKEDEV script in the
/dev
directory for the appropriate interface, as shown below.

cd /dev
MAKEDEV ex0 ex1 eg0 eg1 ... ie0

I/O COMMANDS

Standard I/O commands are used with raw Ethernet I/O as listed below.

open

The interface name described above is used on the open call. The flags value can be set to O_NDELAY or O_NONBLOCK to indicate that non-blocking I/O is to be done. The open will fail if the specified interface does not exist [ENOENT or ENXIO] or was not found during system initialization. The same or multiple processes may have the same raw Ethernet device open simultaneously. Each open file descriptor will have its own set of raw options (set by ioctl commands) and can be sending and receiving at the same time.

close

The file descriptor is closed. Any messages not yet read are discarded. If this is the last process using the hardware interface, a command is issued to cause it to stop reception.

read

Each read command will return at most one Ethernet message. When the call is issued and there is a message available, the message is returned immediately. The data begins with the 14-byte Ethernet header including source and destination station addresses. If a message is longer than the specified read count, the excess is discarded. The number of bytes copied into the user buffer is returned on the call. If no data is available when the call is made, the process is suspended unless the device has been opened in non-blocking mode. Non-blocking mode reads may return [EWOULDBLOCK], [EAGAIN], or 0 depending upon the way in which non-blocking was specified.

write

The buffer passed by the user must contain the 14-byte Ethernet header with valid destination and source addresses. The user must ensure that the buffer length does not exceed the maximum transmission unit size for the interface; failure to do so may return the [EMSGSIZE] error code. If there are too many untransmitted requests queued at the physical interface driver, the calling process may receive an [ENOBUFS] error. In this case, the request should be resubmitted after a short delay.

select

The select() call can be used to check for the presence of a message to be read by specifying the appropriate values for the readfds. The writefds value can be used to ensure that the system is not out of internal mbuf structures. readfds and writefds are parameters to the select() call containing file descriptors and are explained in that manual-page.

ioctl

The following ioctl commands are applicable to the raw Ethernet interface:

FIOASYNC Set or clear asynchronous I/O functionality on the file descriptor. If the field pointed to by arg is zero, synchronous mode is used. This is also the default mode. In this mode the process will not receive any special notification when there is data available to read. If the field referred to by arg is nonzero, the asynchronous I/O mode is set. In this mode the process or process group will receive notification by means of a SIGIO signal when there is data available to read. When a process is blocked on a select(2), SIGIO will also result when sufficient mbufs are available to change from the unwritable state to being writable.

FIONBIO Set or clear non-blocking I/O functionality on the file descriptor. If the field pointed to by arg is set to zero, the file descriptor is set to blocking I/O mode. This is the default unless the open() call specified non-blocking. If the field referred to by arg contains a nonzero value, the socket non-blocking mode will be set. Read or write calls which cannot complete immediately will return a -1 with errno set to [EAGAIN].

FIONREAD Return the number of bytes of data available to be read on the file descriptor. The result is returned in the field referred to by arg.

The next few ioctl commands use an ifreq structure to pass or return information regarding network addresses. The ifreq structure is defined in <net/if.h> as follows:

structifreq {
charifr_name[16];/∗ name of interface (e.g. ex0) ∗/
union {
structsockaddr ifru_addr;
structsockaddr ifru_dstaddr;
structsockaddr ifru_broadaddr;
shortifru_flags;
intifru_metric;
caddr_tifru_data;
} ifr_ifru;
}
#define ifr_addrifr_ifru.ifru_addr/∗ address ∗/
#define ifr_broadaddrifr_ifru.ifru_broadaddr/∗ address ∗/

The ifr_name field contains the interface name. The size of this field is the maximum size of an interface name, and it consists of a null-terminated ASCII string. The null byte is counted as part of the size of the name. The ifr_flags field provides information on the state of a network interface by inclusive ORing of zero or more of the following flags located in <net/if.h>:

IFF_UP0x1 /∗ Check a single bit to know if interface is up ∗/
IFF_BROADCAST0x2 /∗ Broadcast address valid ∗/
IFF_FDDI0x4 /∗ Indicates an FDDI network interface ∗/
IFF_LOOPBACK0x8 /∗ Interface associated with loop-back network ∗/
IFF_POINTTOPOINT0x10 /∗ Interface is point-to-point link ∗/
IFF_NOTRAILERS0x20 /∗ Avoid use of trailers ∗/
IFF_RUNNING0x40 /∗ Interface associated with functional network device ∗/
IFF_NOARP0x80 /∗ No address resolution protocol ∗/
IFF_PROMISC0x100 /∗ Reserved: Receive all packets ∗/
IFF_ALLMULTI0x200 /∗ Reserved: Receive all multicast packets ∗/
IFF_IP80220x800 /∗ Internet Packets use 802.2 LLC formatting ∗/

The following ioctl commands use an arg which is a pointer to an ifreq structure:

SIOCGIFFLAGS Get the interface flags associated with a particular network interface. The ifr_name field of the ifreq structure referenced by arg should be set to the desired interface name. Upon successful completion, the system will return the flags for the interface in the ifr_ifru.ifru_flags field.

SIOCSIFFLAGS Set the interface flags associated with a particular network interface. The ifr_name field of the ifreq structure referenced by arg should be initialized by the calling program for the desired interface as well as the flags to be set in the ifr_ifru.ifru_flags field. Upon successful completion, the system will set the flags for the interface. If the interface was previously up (IFF_UP set) and is requested to be marked down (IFF_UP not set) then the hardware interface is disabled so long as there are no processes currently having an open raw Ethernet connection to the device.

SIOCGETETADDR
Get the hardware interface receive address. The ifr_name field is not required. The 6-byte Ethernet hardware receive address currently in use by the interface attached to the specified file descriptor is returned in the ifr_ifru.ifru_addr.sa_data field.

SIOCGETFEADDR
Get the hardware interface factory address. The ifr_name field is not required. The 6-byte Ethernet factory-set hardware receive address for the interface attached to the specified file descriptor is returned in the ifr_ifru.ifru_addr.sa_data field.

SIOCSETETADDR
Set the hardware interface receive address. The ifr_name field is not required. The 6-byte Ethernet hardware receive address for the interface attached to the specified file descriptor is set to the first six bytes in the ifr_ifru.ifru_addr.sa_data field.

The remaining ioctl commands use individual data structures unique to the command as listed below:

REIOSETMCAST
Set multicast address. The arg value points to a 6-byte array containing a valid multicast address to be set into the hardware interface. If the specified address is already set as a multicast address, the [EADDRINUSE] error will be returned. If the interface’s multicast address table is full, [ENOMEM] is returned.

REIOCLRMCAST
Clear multicast address. The arg value points to a 6-byte array containing a previously set multicast address. The entry is cleared from the table and removed from the hardware interface. If the specified value is not a currently active multicast address, no error is returned. If all six bytes are set to 0xff, then the entire multicast address table for the interface is cleared.

REIOGETMCAST
Get multicast address table. The arg value points to a reio_mcast structure defined in <net/if.h> as follows:

struct reio_mcast {
intsize;
unsigned char data[96];
}

Upon return, each currently enabled multicast address will be placed in consecutive 6-byte positions in data, and size will be set to the number of valid bytes returned in the array.

REIOSETTYPE Enable reception of raw Ethernet messages and specify which are to be received. This command is used to select which of the messages being received on the interface opened by the file descriptor are to be passed back to the calling program. Until it is issued, no data is received. arg points to a reio_opt structure defined in <net/rif.h> as follows:

struct reio_opt {
intopt;/∗ options word ∗/
intlow_type;/∗ lower bound of types ∗/
inthi_type;/∗ upper bound of types ∗/
}
#defineREIO_80230x01/∗ accept all 802.3 packets ∗/
#define REIO_CLR0x02/∗ clear types table ∗/
#define REIO_PROMIS0x04/∗ place interface in promiscuous mode ∗/

The types used with this command are the 2-byte Ethernet message types which immediately follow the 6-byte source station address in the Ethernet header, or they are the Ethernet type fields in the SNAP header when using IEEE 802.2 Logical Link Control formatted messages. For each call containing valid type(s), those type(s) are appended to the list of message types being received by the particular file descriptor. However, if REIO_CLR is set, the existing table is first cleared before setting the types specified in the current command. If low_type is set to -1, then all message types are to be received by the current interface. A single type is specified by having that type set in low_type with hi_type set to zero. A range of types is specified with the lower bound in low_type and the upper value in hi_type. The [EBUSY] error is returned if an attempt is made to receive a type already being received by another file descriptor. This error is also returned when an attempt is made to receive all messages and the Internet protocol is currently active. The REIO_8023 bit in the options word can be set to request that all IEEE 802.3 formatted messages be received on the current file descriptor. This condition is cleared when a command is issued without this bit set. The REIO_PROMIS bit in the options word can be set to have the hardware interface placed in promiscuous mode; that is, it will receive all traffic on the Ethernet wire regardless of the destination address of the message. This condition is cleared by issuing this same ioctl command without the REIO_PROMIS bit.

RLIOSETADDR Enable reception of raw IEEE 802.2 LLC formatted Ethernet messages and specify which are to be received. This command is used to select which of the messages being received on the interface opened by the file descriptor are to be passed back to the calling program. Until it is issued, no data is received. The file descriptor must have been opened on the llc version of the interface. arg points to a rlio_opt structure defined in <net/rif.h> as follows:

struct rlio_opt {
intopt;/∗ options word ∗/
unsigned char filler[3];
unsigned charaddr;/∗ 802.2 LLC address ∗/
}
#define RLIO_CLR0x02/∗ clear address table ∗/
#define RLIO_NO_INET0x08/∗ don’t inc IP msgs ∗/

The addresses used with this command are the IEEE 802.2 LLC DSAPs (Destination Service Access Points) which are contained in the 802.2 LLC header following the Ethernet header. For each call containing valid addr(s), those addr(s) are appended to the list of DSAP addresses being received by the particular file descriptor. However, if RLIO_CLR is set, the existing table is first cleared before setting the addresses specified in the current command. If addr is set to 255, then all DSAP addresses are to be received by the current interface. A single DSAP address is specified by having that address set in addr. The [EBUSY] error is returned if an attempt is made to receive an address already being received by another file descriptor. This error is also returned when an attempt is made to receive all addresses and the Internet protocol is currently active.
The RLIO_NO_INET bit in the options word can be set to exclude address 170 on a call which is requested all DSAP addresses. 170 is used for the SNAP protocol, a sub-protocol used when Internet utilizes IEEE 802.2. This condition is cleared when a command is issued without this bit set.

FILES

/dev/ex0, /dev/ex0llc
/dev/ie0, /dev/ie0llc
/dev/eg0, /dev/eg0llc

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