| .. SPDX-License-Identifier: GPL-2.0 |
| |
| 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 Packet |
| Layer and the X.25 device driver. They are designed to allow for the easy |
| setting of the LAPB mode from within the Packet Layer. |
| |
| The X.25 device driver will be coded normally as per the Linux device driver |
| standards. Most X.25 device drivers will be moderately similar to the |
| already existing Ethernet device drivers. However unlike those drivers, the |
| X.25 device driver has a state associated with it, and this information |
| needs 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 transmitted |
| over the LAPB link. The first byte of the skbuff indicates the meaning of |
| the 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 transmitted |
| over the LAPB link. The LAPB link should already exist before any data is |
| passed down. |
| |
| First Byte = 0x01 (X25_IFACE_CONNECT) |
| |
| Establish the LAPB link. If the link is already established then the connect |
| confirmation 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 disconnect |
| confirmation 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 been |
| received over the LAPB link. |
| |
| First Byte = 0x01 (X25_IFACE_CONNECT) |
| |
| LAPB link has been established. The same message is used for both a LAPB |
| link 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 LAPB |
| link 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 the |
| Packet Layer and the device driver. |
| |
| To avoid packets from being reordered or dropped when delivering from |
| the device driver to the Packet Layer, the device driver should not |
| call "netif_rx" to deliver the received packets. Instead, it should |
| call "netif_receive_skb_core" from softirq context to deliver them. |
