306 lines
11 KiB
ReStructuredText
306 lines
11 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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===============================
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The Linux LAPB Module Interface
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===============================
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Version 1.3
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Jonathan Naylor 29.12.96
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Changed (Henner Eisen, 2000-10-29): int return value for data_indication()
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The LAPB module will be a separately compiled module for use by any parts of
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the Linux operating system that require a LAPB service. This document
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defines the interfaces to, and the services provided by this module. The
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term module in this context does not imply that the LAPB module is a
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separately loadable module, although it may be. The term module is used in
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its more standard meaning.
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The interface to the LAPB module consists of functions to the module,
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callbacks from the module to indicate important state changes, and
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structures for getting and setting information about the module.
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Structures
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----------
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Probably the most important structure is the skbuff structure for holding
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received and transmitted data, however it is beyond the scope of this
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document.
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The two LAPB specific structures are the LAPB initialisation structure and
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the LAPB parameter structure. These will be defined in a standard header
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file, <linux/lapb.h>. The header file <net/lapb.h> is internal to the LAPB
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module and is not for use.
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LAPB Initialisation Structure
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-----------------------------
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This structure is used only once, in the call to lapb_register (see below).
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It contains information about the device driver that requires the services
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of the LAPB module::
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struct lapb_register_struct {
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void (*connect_confirmation)(int token, int reason);
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void (*connect_indication)(int token, int reason);
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void (*disconnect_confirmation)(int token, int reason);
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void (*disconnect_indication)(int token, int reason);
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int (*data_indication)(int token, struct sk_buff *skb);
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void (*data_transmit)(int token, struct sk_buff *skb);
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};
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Each member of this structure corresponds to a function in the device driver
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that is called when a particular event in the LAPB module occurs. These will
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be described in detail below. If a callback is not required (!!) then a NULL
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may be substituted.
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LAPB Parameter Structure
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------------------------
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This structure is used with the lapb_getparms and lapb_setparms functions
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(see below). They are used to allow the device driver to get and set the
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operational parameters of the LAPB implementation for a given connection::
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struct lapb_parms_struct {
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unsigned int t1;
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unsigned int t1timer;
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unsigned int t2;
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unsigned int t2timer;
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unsigned int n2;
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unsigned int n2count;
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unsigned int window;
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unsigned int state;
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unsigned int mode;
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};
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T1 and T2 are protocol timing parameters and are given in units of 100ms. N2
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is the maximum number of tries on the link before it is declared a failure.
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The window size is the maximum number of outstanding data packets allowed to
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be unacknowledged by the remote end, the value of the window is between 1
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and 7 for a standard LAPB link, and between 1 and 127 for an extended LAPB
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link.
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The mode variable is a bit field used for setting (at present) three values.
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The bit fields have the following meanings:
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====== =================================================
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Bit Meaning
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====== =================================================
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0 LAPB operation (0=LAPB_STANDARD 1=LAPB_EXTENDED).
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1 [SM]LP operation (0=LAPB_SLP 1=LAPB=MLP).
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2 DTE/DCE operation (0=LAPB_DTE 1=LAPB_DCE)
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3-31 Reserved, must be 0.
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====== =================================================
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Extended LAPB operation indicates the use of extended sequence numbers and
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consequently larger window sizes, the default is standard LAPB operation.
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MLP operation is the same as SLP operation except that the addresses used by
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LAPB are different to indicate the mode of operation, the default is Single
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Link Procedure. The difference between DCE and DTE operation is (i) the
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addresses used for commands and responses, and (ii) when the DCE is not
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connected, it sends DM without polls set, every T1. The upper case constant
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names will be defined in the public LAPB header file.
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Functions
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---------
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The LAPB module provides a number of function entry points.
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::
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int lapb_register(void *token, struct lapb_register_struct);
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This must be called before the LAPB module may be used. If the call is
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successful then LAPB_OK is returned. The token must be a unique identifier
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generated by the device driver to allow for the unique identification of the
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instance of the LAPB link. It is returned by the LAPB module in all of the
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callbacks, and is used by the device driver in all calls to the LAPB module.
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For multiple LAPB links in a single device driver, multiple calls to
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lapb_register must be made. The format of the lapb_register_struct is given
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above. The return values are:
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============= =============================
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LAPB_OK LAPB registered successfully.
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LAPB_BADTOKEN Token is already registered.
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LAPB_NOMEM Out of memory
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============= =============================
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::
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int lapb_unregister(void *token);
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This releases all the resources associated with a LAPB link. Any current
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LAPB link will be abandoned without further messages being passed. After
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this call, the value of token is no longer valid for any calls to the LAPB
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function. The valid return values are:
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============= ===============================
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LAPB_OK LAPB unregistered successfully.
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LAPB_BADTOKEN Invalid/unknown LAPB token.
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============= ===============================
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::
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int lapb_getparms(void *token, struct lapb_parms_struct *parms);
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This allows the device driver to get the values of the current LAPB
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variables, the lapb_parms_struct is described above. The valid return values
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are:
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============= =============================
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LAPB_OK LAPB getparms was successful.
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LAPB_BADTOKEN Invalid/unknown LAPB token.
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============= =============================
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::
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int lapb_setparms(void *token, struct lapb_parms_struct *parms);
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This allows the device driver to set the values of the current LAPB
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variables, the lapb_parms_struct is described above. The values of t1timer,
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t2timer and n2count are ignored, likewise changing the mode bits when
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connected will be ignored. An error implies that none of the values have
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been changed. The valid return values are:
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============= =================================================
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LAPB_OK LAPB getparms was successful.
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LAPB_BADTOKEN Invalid/unknown LAPB token.
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LAPB_INVALUE One of the values was out of its allowable range.
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============= =================================================
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::
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int lapb_connect_request(void *token);
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Initiate a connect using the current parameter settings. The valid return
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values are:
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============== =================================
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LAPB_OK LAPB is starting to connect.
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LAPB_BADTOKEN Invalid/unknown LAPB token.
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LAPB_CONNECTED LAPB module is already connected.
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============== =================================
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::
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int lapb_disconnect_request(void *token);
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Initiate a disconnect. The valid return values are:
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================= ===============================
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LAPB_OK LAPB is starting to disconnect.
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LAPB_BADTOKEN Invalid/unknown LAPB token.
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LAPB_NOTCONNECTED LAPB module is not connected.
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================= ===============================
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::
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int lapb_data_request(void *token, struct sk_buff *skb);
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Queue data with the LAPB module for transmitting over the link. If the call
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is successful then the skbuff is owned by the LAPB module and may not be
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used by the device driver again. The valid return values are:
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================= =============================
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LAPB_OK LAPB has accepted the data.
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LAPB_BADTOKEN Invalid/unknown LAPB token.
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LAPB_NOTCONNECTED LAPB module is not connected.
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================= =============================
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::
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int lapb_data_received(void *token, struct sk_buff *skb);
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Queue data with the LAPB module which has been received from the device. It
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is expected that the data passed to the LAPB module has skb->data pointing
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to the beginning of the LAPB data. If the call is successful then the skbuff
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is owned by the LAPB module and may not be used by the device driver again.
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The valid return values are:
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============= ===========================
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LAPB_OK LAPB has accepted the data.
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LAPB_BADTOKEN Invalid/unknown LAPB token.
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============= ===========================
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Callbacks
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---------
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These callbacks are functions provided by the device driver for the LAPB
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module to call when an event occurs. They are registered with the LAPB
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module with lapb_register (see above) in the structure lapb_register_struct
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(see above).
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::
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void (*connect_confirmation)(void *token, int reason);
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This is called by the LAPB module when a connection is established after
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being requested by a call to lapb_connect_request (see above). The reason is
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always LAPB_OK.
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::
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void (*connect_indication)(void *token, int reason);
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This is called by the LAPB module when the link is established by the remote
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system. The value of reason is always LAPB_OK.
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::
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void (*disconnect_confirmation)(void *token, int reason);
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This is called by the LAPB module when an event occurs after the device
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driver has called lapb_disconnect_request (see above). The reason indicates
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what has happened. In all cases the LAPB link can be regarded as being
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terminated. The values for reason are:
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================= ====================================================
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LAPB_OK The LAPB link was terminated normally.
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LAPB_NOTCONNECTED The remote system was not connected.
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LAPB_TIMEDOUT No response was received in N2 tries from the remote
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system.
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================= ====================================================
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::
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void (*disconnect_indication)(void *token, int reason);
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This is called by the LAPB module when the link is terminated by the remote
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system or another event has occurred to terminate the link. This may be
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returned in response to a lapb_connect_request (see above) if the remote
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system refused the request. The values for reason are:
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================= ====================================================
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LAPB_OK The LAPB link was terminated normally by the remote
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system.
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LAPB_REFUSED The remote system refused the connect request.
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LAPB_NOTCONNECTED The remote system was not connected.
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LAPB_TIMEDOUT No response was received in N2 tries from the remote
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system.
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================= ====================================================
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::
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int (*data_indication)(void *token, struct sk_buff *skb);
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This is called by the LAPB module when data has been received from the
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remote system that should be passed onto the next layer in the protocol
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stack. The skbuff becomes the property of the device driver and the LAPB
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module will not perform any more actions on it. The skb->data pointer will
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be pointing to the first byte of data after the LAPB header.
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This method should return NET_RX_DROP (as defined in the header
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file include/linux/netdevice.h) if and only if the frame was dropped
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before it could be delivered to the upper layer.
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void (*data_transmit)(void *token, struct sk_buff *skb);
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This is called by the LAPB module when data is to be transmitted to the
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remote system by the device driver. The skbuff becomes the property of the
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device driver and the LAPB module will not perform any more actions on it.
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The skb->data pointer will be pointing to the first byte of the LAPB header.
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