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