337 lines
12 KiB
ReStructuredText
337 lines
12 KiB
ReStructuredText
=========================================
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Kernel CAPI Interface to Hardware Drivers
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=========================================
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1. Overview
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===========
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From the CAPI 2.0 specification:
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COMMON-ISDN-API (CAPI) is an application programming interface standard used
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to access ISDN equipment connected to basic rate interfaces (BRI) and primary
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rate interfaces (PRI).
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Kernel CAPI operates as a dispatching layer between CAPI applications and CAPI
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hardware drivers. Hardware drivers register ISDN devices (controllers, in CAPI
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lingo) with Kernel CAPI to indicate their readiness to provide their service
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to CAPI applications. CAPI applications also register with Kernel CAPI,
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requesting association with a CAPI device. Kernel CAPI then dispatches the
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application registration to an available device, forwarding it to the
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corresponding hardware driver. Kernel CAPI then forwards CAPI messages in both
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directions between the application and the hardware driver.
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Format and semantics of CAPI messages are specified in the CAPI 2.0 standard.
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This standard is freely available from https://www.capi.org.
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2. Driver and Device Registration
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=================================
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CAPI drivers must register each of the ISDN devices they control with Kernel
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CAPI by calling the Kernel CAPI function attach_capi_ctr() with a pointer to a
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struct capi_ctr before they can be used. This structure must be filled with
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the names of the driver and controller, and a number of callback function
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pointers which are subsequently used by Kernel CAPI for communicating with the
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driver. The registration can be revoked by calling the function
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detach_capi_ctr() with a pointer to the same struct capi_ctr.
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Before the device can be actually used, the driver must fill in the device
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information fields 'manu', 'version', 'profile' and 'serial' in the capi_ctr
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structure of the device, and signal its readiness by calling capi_ctr_ready().
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From then on, Kernel CAPI may call the registered callback functions for the
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device.
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If the device becomes unusable for any reason (shutdown, disconnect ...), the
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driver has to call capi_ctr_down(). This will prevent further calls to the
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callback functions by Kernel CAPI.
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3. Application Registration and Communication
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=============================================
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Kernel CAPI forwards registration requests from applications (calls to CAPI
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operation CAPI_REGISTER) to an appropriate hardware driver by calling its
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register_appl() callback function. A unique Application ID (ApplID, u16) is
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allocated by Kernel CAPI and passed to register_appl() along with the
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parameter structure provided by the application. This is analogous to the
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open() operation on regular files or character devices.
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After a successful return from register_appl(), CAPI messages from the
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application may be passed to the driver for the device via calls to the
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send_message() callback function. Conversely, the driver may call Kernel
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CAPI's capi_ctr_handle_message() function to pass a received CAPI message to
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Kernel CAPI for forwarding to an application, specifying its ApplID.
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Deregistration requests (CAPI operation CAPI_RELEASE) from applications are
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forwarded as calls to the release_appl() callback function, passing the same
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ApplID as with register_appl(). After return from release_appl(), no CAPI
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messages for that application may be passed to or from the device anymore.
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4. Data Structures
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==================
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4.1 struct capi_driver
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----------------------
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This structure describes a Kernel CAPI driver itself. It is used in the
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register_capi_driver() and unregister_capi_driver() functions, and contains
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the following non-private fields, all to be set by the driver before calling
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register_capi_driver():
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``char name[32]``
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the name of the driver, as a zero-terminated ASCII string
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``char revision[32]``
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the revision number of the driver, as a zero-terminated ASCII string
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4.2 struct capi_ctr
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-------------------
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This structure describes an ISDN device (controller) handled by a Kernel CAPI
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driver. After registration via the attach_capi_ctr() function it is passed to
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all controller specific lower layer interface and callback functions to
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identify the controller to operate on.
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It contains the following non-private fields:
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to be set by the driver before calling attach_capi_ctr():
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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``struct module *owner``
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pointer to the driver module owning the device
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``void *driverdata``
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an opaque pointer to driver specific data, not touched by Kernel CAPI
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``char name[32]``
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the name of the controller, as a zero-terminated ASCII string
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``char *driver_name``
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the name of the driver, as a zero-terminated ASCII string
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``int (*load_firmware)(struct capi_ctr *ctrlr, capiloaddata *ldata)``
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(optional) pointer to a callback function for sending firmware and
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configuration data to the device
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The function may return before the operation has completed.
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Completion must be signalled by a call to capi_ctr_ready().
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Return value: 0 on success, error code on error
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Called in process context.
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``void (*reset_ctr)(struct capi_ctr *ctrlr)``
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(optional) pointer to a callback function for stopping the device,
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releasing all registered applications
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The function may return before the operation has completed.
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Completion must be signalled by a call to capi_ctr_down().
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Called in process context.
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``void (*register_appl)(struct capi_ctr *ctrlr, u16 applid, capi_register_params *rparam)``
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pointers to callback function for registration of
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applications with the device
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Calls to these functions are serialized by Kernel CAPI so that only
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one call to any of them is active at any time.
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``void (*release_appl)(struct capi_ctr *ctrlr, u16 applid)``
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pointers to callback functions deregistration of
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applications with the device
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Calls to these functions are serialized by Kernel CAPI so that only
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one call to any of them is active at any time.
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``u16 (*send_message)(struct capi_ctr *ctrlr, struct sk_buff *skb)``
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pointer to a callback function for sending a CAPI message to the
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device
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Return value: CAPI error code
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If the method returns 0 (CAPI_NOERROR) the driver has taken ownership
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of the skb and the caller may no longer access it. If it returns a
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non-zero (error) value then ownership of the skb returns to the caller
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who may reuse or free it.
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The return value should only be used to signal problems with respect
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to accepting or queueing the message. Errors occurring during the
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actual processing of the message should be signaled with an
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appropriate reply message.
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May be called in process or interrupt context.
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Calls to this function are not serialized by Kernel CAPI, ie. it must
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be prepared to be re-entered.
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``char *(*procinfo)(struct capi_ctr *ctrlr)``
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pointer to a callback function returning the entry for the device in
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the CAPI controller info table, /proc/capi/controller
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Note:
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Callback functions except send_message() are never called in interrupt
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context.
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to be filled in before calling capi_ctr_ready():
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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``u8 manu[CAPI_MANUFACTURER_LEN]``
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value to return for CAPI_GET_MANUFACTURER
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``capi_version version``
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value to return for CAPI_GET_VERSION
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``capi_profile profile``
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value to return for CAPI_GET_PROFILE
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``u8 serial[CAPI_SERIAL_LEN]``
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value to return for CAPI_GET_SERIAL
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4.3 SKBs
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--------
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CAPI messages are passed between Kernel CAPI and the driver via send_message()
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and capi_ctr_handle_message(), stored in the data portion of a socket buffer
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(skb). Each skb contains a single CAPI message coded according to the CAPI 2.0
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standard.
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For the data transfer messages, DATA_B3_REQ and DATA_B3_IND, the actual
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payload data immediately follows the CAPI message itself within the same skb.
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The Data and Data64 parameters are not used for processing. The Data64
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parameter may be omitted by setting the length field of the CAPI message to 22
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instead of 30.
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4.4 The _cmsg Structure
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-----------------------
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(declared in <linux/isdn/capiutil.h>)
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The _cmsg structure stores the contents of a CAPI 2.0 message in an easily
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accessible form. It contains members for all possible CAPI 2.0 parameters,
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including subparameters of the Additional Info and B Protocol structured
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parameters, with the following exceptions:
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* second Calling party number (CONNECT_IND)
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* Data64 (DATA_B3_REQ and DATA_B3_IND)
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* Sending complete (subparameter of Additional Info, CONNECT_REQ and INFO_REQ)
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* Global Configuration (subparameter of B Protocol, CONNECT_REQ, CONNECT_RESP
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and SELECT_B_PROTOCOL_REQ)
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Only those parameters appearing in the message type currently being processed
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are actually used. Unused members should be set to zero.
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Members are named after the CAPI 2.0 standard names of the parameters they
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represent. See <linux/isdn/capiutil.h> for the exact spelling. Member data
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types are:
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=========== =================================================================
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u8 for CAPI parameters of type 'byte'
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u16 for CAPI parameters of type 'word'
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u32 for CAPI parameters of type 'dword'
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_cstruct for CAPI parameters of type 'struct'
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The member is a pointer to a buffer containing the parameter in
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CAPI encoding (length + content). It may also be NULL, which will
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be taken to represent an empty (zero length) parameter.
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Subparameters are stored in encoded form within the content part.
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_cmstruct alternative representation for CAPI parameters of type 'struct'
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(used only for the 'Additional Info' and 'B Protocol' parameters)
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The representation is a single byte containing one of the values:
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CAPI_DEFAULT: The parameter is empty/absent.
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CAPI_COMPOSE: The parameter is present.
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Subparameter values are stored individually in the corresponding
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_cmsg structure members.
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=========== =================================================================
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5. Lower Layer Interface Functions
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==================================
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::
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int attach_capi_ctr(struct capi_ctr *ctrlr)
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int detach_capi_ctr(struct capi_ctr *ctrlr)
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register/unregister a device (controller) with Kernel CAPI
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::
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void capi_ctr_ready(struct capi_ctr *ctrlr)
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void capi_ctr_down(struct capi_ctr *ctrlr)
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signal controller ready/not ready
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::
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void capi_ctr_handle_message(struct capi_ctr * ctrlr, u16 applid,
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struct sk_buff *skb)
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pass a received CAPI message to Kernel CAPI
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for forwarding to the specified application
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6. Helper Functions and Macros
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==============================
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Macros to extract/set element values from/in a CAPI message header
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(from <linux/isdn/capiutil.h>):
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====================== ============================= ====================
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Get Macro Set Macro Element (Type)
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====================== ============================= ====================
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CAPIMSG_LEN(m) CAPIMSG_SETLEN(m, len) Total Length (u16)
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CAPIMSG_APPID(m) CAPIMSG_SETAPPID(m, applid) ApplID (u16)
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CAPIMSG_COMMAND(m) CAPIMSG_SETCOMMAND(m,cmd) Command (u8)
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CAPIMSG_SUBCOMMAND(m) CAPIMSG_SETSUBCOMMAND(m, cmd) Subcommand (u8)
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CAPIMSG_CMD(m) - Command*256
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+ Subcommand (u16)
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CAPIMSG_MSGID(m) CAPIMSG_SETMSGID(m, msgid) Message Number (u16)
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CAPIMSG_CONTROL(m) CAPIMSG_SETCONTROL(m, contr) Controller/PLCI/NCCI
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(u32)
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CAPIMSG_DATALEN(m) CAPIMSG_SETDATALEN(m, len) Data Length (u16)
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====================== ============================= ====================
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Library functions for working with _cmsg structures
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(from <linux/isdn/capiutil.h>):
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``char *capi_cmd2str(u8 Command, u8 Subcommand)``
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Returns the CAPI 2.0 message name corresponding to the given command
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and subcommand values, as a static ASCII string. The return value may
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be NULL if the command/subcommand is not one of those defined in the
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CAPI 2.0 standard.
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7. Debugging
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============
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The module kernelcapi has a module parameter showcapimsgs controlling some
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debugging output produced by the module. It can only be set when the module is
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loaded, via a parameter "showcapimsgs=<n>" to the modprobe command, either on
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the command line or in the configuration file.
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If the lowest bit of showcapimsgs is set, kernelcapi logs controller and
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application up and down events.
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In addition, every registered CAPI controller has an associated traceflag
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parameter controlling how CAPI messages sent from and to tha controller are
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logged. The traceflag parameter is initialized with the value of the
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showcapimsgs parameter when the controller is registered, but can later be
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changed via the MANUFACTURER_REQ command KCAPI_CMD_TRACE.
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If the value of traceflag is non-zero, CAPI messages are logged.
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DATA_B3 messages are only logged if the value of traceflag is > 2.
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If the lowest bit of traceflag is set, only the command/subcommand and message
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length are logged. Otherwise, kernelcapi logs a readable representation of
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the entire message.
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