0001 .. SPDX-License-Identifier: GPL-2.0
0002
0003 ============================-
0004 X.25 Device Driver Interface
0005 ============================-
0006
0007 Version 1.1
0008
0009 Jonathan Naylor 26.12.96
0010
0011 This is a description of the messages to be passed between the X.25 Packet
0012 Layer and the X.25 device driver. They are designed to allow for the easy
0013 setting of the LAPB mode from within the Packet Layer.
0014
0015 The X.25 device driver will be coded normally as per the Linux device driver
0016 standards. Most X.25 device drivers will be moderately similar to the
0017 already existing Ethernet device drivers. However unlike those drivers, the
0018 X.25 device driver has a state associated with it, and this information
0019 needs to be passed to and from the Packet Layer for proper operation.
0020
0021 All messages are held in sk_buff's just like real data to be transmitted
0022 over the LAPB link. The first byte of the skbuff indicates the meaning of
0023 the rest of the skbuff, if any more information does exist.
0024
0025
0026 Packet Layer to Device Driver
0027 -----------------------------
0028
0029 First Byte = 0x00 (X25_IFACE_DATA)
0030
0031 This indicates that the rest of the skbuff contains data to be transmitted
0032 over the LAPB link. The LAPB link should already exist before any data is
0033 passed down.
0034
0035 First Byte = 0x01 (X25_IFACE_CONNECT)
0036
0037 Establish the LAPB link. If the link is already established then the connect
0038 confirmation message should be returned as soon as possible.
0039
0040 First Byte = 0x02 (X25_IFACE_DISCONNECT)
0041
0042 Terminate the LAPB link. If it is already disconnected then the disconnect
0043 confirmation message should be returned as soon as possible.
0044
0045 First Byte = 0x03 (X25_IFACE_PARAMS)
0046
0047 LAPB parameters. To be defined.
0048
0049
0050 Device Driver to Packet Layer
0051 -----------------------------
0052
0053 First Byte = 0x00 (X25_IFACE_DATA)
0054
0055 This indicates that the rest of the skbuff contains data that has been
0056 received over the LAPB link.
0057
0058 First Byte = 0x01 (X25_IFACE_CONNECT)
0059
0060 LAPB link has been established. The same message is used for both a LAPB
0061 link connect_confirmation and a connect_indication.
0062
0063 First Byte = 0x02 (X25_IFACE_DISCONNECT)
0064
0065 LAPB link has been terminated. This same message is used for both a LAPB
0066 link disconnect_confirmation and a disconnect_indication.
0067
0068 First Byte = 0x03 (X25_IFACE_PARAMS)
0069
0070 LAPB parameters. To be defined.
0071
0072
0073 Requirements for the device driver
0074 ----------------------------------
0075
0076 Packets should not be reordered or dropped when delivering between the
0077 Packet Layer and the device driver.
0078
0079 To avoid packets from being reordered or dropped when delivering from
0080 the device driver to the Packet Layer, the device driver should not
0081 call "netif_rx" to deliver the received packets. Instead, it should
0082 call "netif_receive_skb_core" from softirq context to deliver them.
