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1.. SPDX-License-Identifier: GPL-2.0
2
3===============================
4The Linux LAPB Module Interface
5===============================
6
7Version 1.3
8
9Jonathan Naylor 29.12.96
10
11Changed (Henner Eisen, 2000-10-29): int return value for data_indication()
12
13The LAPB module will be a separately compiled module for use by any parts of
14the Linux operating system that require a LAPB service. This document
15defines the interfaces to, and the services provided by this module. The
16term module in this context does not imply that the LAPB module is a
17separately loadable module, although it may be. The term module is used in
18its more standard meaning.
19
20The interface to the LAPB module consists of functions to the module,
21callbacks from the module to indicate important state changes, and
22structures for getting and setting information about the module.
23
24Structures
25----------
26
27Probably the most important structure is the skbuff structure for holding
28received and transmitted data, however it is beyond the scope of this
29document.
30
31The two LAPB specific structures are the LAPB initialisation structure and
32the LAPB parameter structure. These will be defined in a standard header
33file, <linux/lapb.h>. The header file <net/lapb.h> is internal to the LAPB
34module and is not for use.
35
36LAPB Initialisation Structure
37-----------------------------
38
39This structure is used only once, in the call to lapb_register (see below).
40It contains information about the device driver that requires the services
41of the LAPB module::
42
43 struct lapb_register_struct {
44 void (*connect_confirmation)(int token, int reason);
45 void (*connect_indication)(int token, int reason);
46 void (*disconnect_confirmation)(int token, int reason);
47 void (*disconnect_indication)(int token, int reason);
48 int (*data_indication)(int token, struct sk_buff *skb);
49 void (*data_transmit)(int token, struct sk_buff *skb);
50 };
51
52Each member of this structure corresponds to a function in the device driver
53that is called when a particular event in the LAPB module occurs. These will
54be described in detail below. If a callback is not required (!!) then a NULL
55may be substituted.
56
57
58LAPB Parameter Structure
59------------------------
60
61This structure is used with the lapb_getparms and lapb_setparms functions
62(see below). They are used to allow the device driver to get and set the
63operational parameters of the LAPB implementation for a given connection::
64
65 struct lapb_parms_struct {
66 unsigned int t1;
67 unsigned int t1timer;
68 unsigned int t2;
69 unsigned int t2timer;
70 unsigned int n2;
71 unsigned int n2count;
72 unsigned int window;
73 unsigned int state;
74 unsigned int mode;
75 };
76
77T1 and T2 are protocol timing parameters and are given in units of 100ms. N2
78is the maximum number of tries on the link before it is declared a failure.
79The window size is the maximum number of outstanding data packets allowed to
80be unacknowledged by the remote end, the value of the window is between 1
81and 7 for a standard LAPB link, and between 1 and 127 for an extended LAPB
82link.
83
84The mode variable is a bit field used for setting (at present) three values.
85The bit fields have the following meanings:
86
87====== =================================================
88Bit Meaning
89====== =================================================
900 LAPB operation (0=LAPB_STANDARD 1=LAPB_EXTENDED).
911 [SM]LP operation (0=LAPB_SLP 1=LAPB=MLP).
922 DTE/DCE operation (0=LAPB_DTE 1=LAPB_DCE)
933-31 Reserved, must be 0.
94====== =================================================
95
96Extended LAPB operation indicates the use of extended sequence numbers and
97consequently larger window sizes, the default is standard LAPB operation.
98MLP operation is the same as SLP operation except that the addresses used by
99LAPB are different to indicate the mode of operation, the default is Single
100Link Procedure. The difference between DCE and DTE operation is (i) the
101addresses used for commands and responses, and (ii) when the DCE is not
102connected, it sends DM without polls set, every T1. The upper case constant
103names will be defined in the public LAPB header file.
104
105
106Functions
107---------
108
109The LAPB module provides a number of function entry points.
110
111::
112
113 int lapb_register(void *token, struct lapb_register_struct);
114
115This must be called before the LAPB module may be used. If the call is
116successful then LAPB_OK is returned. The token must be a unique identifier
117generated by the device driver to allow for the unique identification of the
118instance of the LAPB link. It is returned by the LAPB module in all of the
119callbacks, and is used by the device driver in all calls to the LAPB module.
120For multiple LAPB links in a single device driver, multiple calls to
121lapb_register must be made. The format of the lapb_register_struct is given
122above. The return values are:
123
124============= =============================
125LAPB_OK LAPB registered successfully.
126LAPB_BADTOKEN Token is already registered.
127LAPB_NOMEM Out of memory
128============= =============================
129
130::
131
132 int lapb_unregister(void *token);
133
134This releases all the resources associated with a LAPB link. Any current
135LAPB link will be abandoned without further messages being passed. After
136this call, the value of token is no longer valid for any calls to the LAPB
137function. The valid return values are:
138
139============= ===============================
140LAPB_OK LAPB unregistered successfully.
141LAPB_BADTOKEN Invalid/unknown LAPB token.
142============= ===============================
143
144::
145
146 int lapb_getparms(void *token, struct lapb_parms_struct *parms);
147
148This allows the device driver to get the values of the current LAPB
149variables, the lapb_parms_struct is described above. The valid return values
150are:
151
152============= =============================
153LAPB_OK LAPB getparms was successful.
154LAPB_BADTOKEN Invalid/unknown LAPB token.
155============= =============================
156
157::
158
159 int lapb_setparms(void *token, struct lapb_parms_struct *parms);
160
161This allows the device driver to set the values of the current LAPB
162variables, the lapb_parms_struct is described above. The values of t1timer,
163t2timer and n2count are ignored, likewise changing the mode bits when
164connected will be ignored. An error implies that none of the values have
165been changed. The valid return values are:
166
167============= =================================================
168LAPB_OK LAPB getparms was successful.
169LAPB_BADTOKEN Invalid/unknown LAPB token.
170LAPB_INVALUE One of the values was out of its allowable range.
171============= =================================================
172
173::
174
175 int lapb_connect_request(void *token);
176
177Initiate a connect using the current parameter settings. The valid return
178values are:
179
180============== =================================
181LAPB_OK LAPB is starting to connect.
182LAPB_BADTOKEN Invalid/unknown LAPB token.
183LAPB_CONNECTED LAPB module is already connected.
184============== =================================
185
186::
187
188 int lapb_disconnect_request(void *token);
189
190Initiate a disconnect. The valid return values are:
191
192================= ===============================
193LAPB_OK LAPB is starting to disconnect.
194LAPB_BADTOKEN Invalid/unknown LAPB token.
195LAPB_NOTCONNECTED LAPB module is not connected.
196================= ===============================
197
198::
199
200 int lapb_data_request(void *token, struct sk_buff *skb);
201
202Queue data with the LAPB module for transmitting over the link. If the call
203is successful then the skbuff is owned by the LAPB module and may not be
204used by the device driver again. The valid return values are:
205
206================= =============================
207LAPB_OK LAPB has accepted the data.
208LAPB_BADTOKEN Invalid/unknown LAPB token.
209LAPB_NOTCONNECTED LAPB module is not connected.
210================= =============================
211
212::
213
214 int lapb_data_received(void *token, struct sk_buff *skb);
215
216Queue data with the LAPB module which has been received from the device. It
217is expected that the data passed to the LAPB module has skb->data pointing
218to the beginning of the LAPB data. If the call is successful then the skbuff
219is owned by the LAPB module and may not be used by the device driver again.
220The valid return values are:
221
222============= ===========================
223LAPB_OK LAPB has accepted the data.
224LAPB_BADTOKEN Invalid/unknown LAPB token.
225============= ===========================
226
227Callbacks
228---------
229
230These callbacks are functions provided by the device driver for the LAPB
231module to call when an event occurs. They are registered with the LAPB
232module with lapb_register (see above) in the structure lapb_register_struct
233(see above).
234
235::
236
237 void (*connect_confirmation)(void *token, int reason);
238
239This is called by the LAPB module when a connection is established after
240being requested by a call to lapb_connect_request (see above). The reason is
241always LAPB_OK.
242
243::
244
245 void (*connect_indication)(void *token, int reason);
246
247This is called by the LAPB module when the link is established by the remote
248system. The value of reason is always LAPB_OK.
249
250::
251
252 void (*disconnect_confirmation)(void *token, int reason);
253
254This is called by the LAPB module when an event occurs after the device
255driver has called lapb_disconnect_request (see above). The reason indicates
256what has happened. In all cases the LAPB link can be regarded as being
257terminated. The values for reason are:
258
259================= ====================================================
260LAPB_OK The LAPB link was terminated normally.
261LAPB_NOTCONNECTED The remote system was not connected.
262LAPB_TIMEDOUT No response was received in N2 tries from the remote
263 system.
264================= ====================================================
265
266::
267
268 void (*disconnect_indication)(void *token, int reason);
269
270This is called by the LAPB module when the link is terminated by the remote
271system or another event has occurred to terminate the link. This may be
272returned in response to a lapb_connect_request (see above) if the remote
273system refused the request. The values for reason are:
274
275================= ====================================================
276LAPB_OK The LAPB link was terminated normally by the remote
277 system.
278LAPB_REFUSED The remote system refused the connect request.
279LAPB_NOTCONNECTED The remote system was not connected.
280LAPB_TIMEDOUT No response was received in N2 tries from the remote
281 system.
282================= ====================================================
283
284::
285
286 int (*data_indication)(void *token, struct sk_buff *skb);
287
288This is called by the LAPB module when data has been received from the
289remote system that should be passed onto the next layer in the protocol
290stack. The skbuff becomes the property of the device driver and the LAPB
291module will not perform any more actions on it. The skb->data pointer will
292be pointing to the first byte of data after the LAPB header.
293
294This method should return NET_RX_DROP (as defined in the header
295file include/linux/netdevice.h) if and only if the frame was dropped
296before it could be delivered to the upper layer.
297
298::
299
300 void (*data_transmit)(void *token, struct sk_buff *skb);
301
302This is called by the LAPB module when data is to be transmitted to the
303remote system by the device driver. The skbuff becomes the property of the
304device driver and the LAPB module will not perform any more actions on it.
305The skb->data pointer will be pointing to the first byte of the LAPB header.