X.25 Device Driver Interface

Version 1.1

Jonathan Naylor 26.12.96

This is a description of the messages to be passed between the X.25 PacketLayer and the X.25 device driver. They are designed to allow for the easysetting of the LAPB mode from within the Packet Layer.

The X.25 device driver will be coded normally as per the Linux device driverstandards. Most X.25 device drivers will be moderately similar to thealready existing Ethernet device drivers. However unlike those drivers, theX.25 device driver has a state associated with it, and this informationneeds to be passed to and from the Packet Layer for proper operation.

All messages are held in sk_buff’s just like real data to be transmittedover the LAPB link. The first byte of the skbuff indicates the meaning ofthe rest of the skbuff, if any more information does exist.

Packet Layer to Device Driver

First Byte = 0x00 (X25_IFACE_DATA)

This indicates that the rest of the skbuff contains data to be transmittedover the LAPB link. The LAPB link should already exist before any data ispassed down.

First Byte = 0x01 (X25_IFACE_CONNECT)

Establish the LAPB link. If the link is already established then the connectconfirmation message should be returned as soon as possible.

First Byte = 0x02 (X25_IFACE_DISCONNECT)

Terminate the LAPB link. If it is already disconnected then the disconnectconfirmation message should be returned as soon as possible.

First Byte = 0x03 (X25_IFACE_PARAMS)

LAPB parameters. To be defined.

Device Driver to Packet Layer

First Byte = 0x00 (X25_IFACE_DATA)

This indicates that the rest of the skbuff contains data that has beenreceived over the LAPB link.

First Byte = 0x01 (X25_IFACE_CONNECT)

LAPB link has been established. The same message is used for both a LAPBlink connect_confirmation and a connect_indication.

First Byte = 0x02 (X25_IFACE_DISCONNECT)

LAPB link has been terminated. This same message is used for both a LAPBlink disconnect_confirmation and a disconnect_indication.

First Byte = 0x03 (X25_IFACE_PARAMS)

LAPB parameters. To be defined.

Requirements for the device driver

Packets should not be reordered or dropped when delivering between thePacket Layer and the device driver.

To avoid packets from being reordered or dropped when delivering fromthe device driver to the Packet Layer, the device driver should notcall “netif_rx” to deliver the received packets. Instead, it shouldcall “netif_receive_skb_core” from softirq context to deliver them.