From 1298c51f516a7bf04ca9add1b7db14417cdc66f3 Mon Sep 17 00:00:00 2001 From: Daniel Drake Date: Mon, 12 May 2008 18:46:37 +0100 Subject: Backend documentation for porting efforts Hopefully comprehensive enough for people to get started. --- libusb/libusbi.h | 347 ++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 341 insertions(+), 6 deletions(-) (limited to 'libusb/libusbi.h') diff --git a/libusb/libusbi.h b/libusb/libusbi.h index 87b2953..015d489 100644 --- a/libusb/libusbi.h +++ b/libusb/libusbi.h @@ -1,6 +1,6 @@ /* * Internal header for libusb - * Copyright (C) 2007 Daniel Drake + * Copyright (C) 2007-2008 Daniel Drake * Copyright (c) 2001 Johannes Erdfelt * * This library is free software; you can redistribute it and/or @@ -251,58 +251,393 @@ struct discovered_devs *discovered_devs_append( /* OS abstraction */ +/* This is the interface that OS backends need to implement. + * All fields are mandatory, except ones explicitly noted as optional. */ struct usbi_os_backend { + /* A human-readable name for your backend, e.g. "Linux usbfs" */ const char *name; + + /* Perform initialization of your backend. You might use this function + * to determine specific capabilities of the system, allocate required + * data structures for later, etc. + * + * This function is called when a libusb user initializes the library + * prior to use. + * + * Return 0 on success, or a LIBUSB_ERROR code on failure. + */ int (*init)(void); + + /* Deinitialization. Optional. This function should destroy anything + * that was set up by init. + * + * This function is called when the user deinitializes the library. + */ void (*exit)(void); + /* Enumerate all the USB devices on the system, returning them in a list + * of discovered devices. + * + * Your implementation should enumerate all devices on the system, + * regardless of whether they have been seen before or not. + * + * When you have found a device, compute a session ID for it. The session + * ID should uniquely represent that particular device for that particular + * connection session since boot (i.e. if you disconnect and reconnect a + * device immediately after, it should be assigned a different session ID). + * If your OS cannot provide a unique session ID as described above, + * presenting a session ID of (bus_number << 8 | device_address) should + * be sufficient. Bus numbers and device addresses wrap and get reused, + * but that is an unlikely case. + * + * After computing a session ID for a device, call + * usbi_get_device_by_session_id(). This function checks if libusb already + * knows about the device, and if so, it provides you with a libusb_device + * structure for it. + * + * If usbi_get_device_by_session_id() returns NULL, it is time to allocate + * a new device structure for the device. Call usbi_alloc_device() to + * obtain a new libusb_device structure with reference count 1. Populate + * the bus_number and device_address attributes of the new device, and + * perform any other internal backend initialization you need to do. At + * this point, you should be ready to provide device descriptors and so + * on through the get_*_descriptor functions. Finally, call + * usbi_sanitize_device() to perform some final sanity checks on the + * device. Assuming all of the above succeeded, we can now continue. + * If any of the above failed, remember to unreference the device that + * was returned by usbi_alloc_device(). + * + * At this stage we have a populated libusb_device structure (either one + * that was found earlier, or one that we have just allocated and + * populated). This can now be added to the discovered devices list + * using discovered_devs_append(). Note that discovered_devs_append() + * may reallocate the list, returning a new location for it, and also + * note that reallocation can fail. Your backend should handle these + * error conditions appropriately. + * + * This function should not generate any bus I/O and should not block. + * If I/O is required (e.g. reading the active configuration value), it is + * OK to ignore these suggestions :) + * + * This function is executed when the user wishes to retrieve a list + * of USB devices connected to the system. + * + * Return 0 on success, or a LIBUSB_ERROR code on failure. + */ int (*get_device_list)(struct discovered_devs **discdevs); + /* Open a device for I/O and other USB operations. The device handle + * is preallocated for you, you can retrieve the device in question + * through handle->dev. + * + * Your backend should allocate any internal resources required for I/O + * and other operations so that those operations can happen (hopefully) + * without hiccup. This is also a good place to inform libusb that it + * should monitor certain file descriptors related to this device - + * see the usbi_add_pollfd() function. + * + * This function should not generate any bus I/O and should not block. + * + * This function is called when the user attempts to obtain a device + * handle for a device. + * + * Return: + * - 0 on success + * - LIBUSB_ERROR_ACCESS if the user has insufficient permissions + * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since + * discovery + * - another LIBUSB_ERROR code on other failure + * + * Do not worry about freeing the handle on failed open, the upper layers + * do this for you. + */ int (*open)(struct libusb_device_handle *handle); + + /* Close a device such that the handle cannot be used again. Your backend + * should destroy any resources that were allocated in the open path. + * This may also be a good place to call usbi_remove_pollfd() to inform + * libusb of any file descriptors associated with this device that should + * no longer be monitored. + * + * This function is called when the user closes a device handle. + */ void (*close)(struct libusb_device_handle *handle); + /* Retrieve the device descriptor from a device. + * + * The descriptor should be retrieved from memory, NOT via bus I/O to the + * device. This means that you may have to cache it in a private structure + * during get_device_list enumeration. Alternatively, you may be able + * to retrieve it from a kernel interface (some Linux setups can do this) + * still without generating bus I/O. + * + * This function is expected to write DEVICE_DESC_LENGTH (18) bytes into + * buffer, which is guaranteed to be big enough. + * + * This function is called when sanity-checking a device before adding + * it to the list of discovered devices, and also when the user requests + * to read the device descriptor. + * + * Return 0 on success or a LIBUSB_ERROR code on failure. + */ int (*get_device_descriptor)(struct libusb_device *device, unsigned char *buffer); + + /* Get the ACTIVE configuration descriptor for a device. + * + * The descriptor should be retrieved from memory, NOT via bus I/O to the + * device. This means that you may have to cache it in a private structure + * during get_device_list enumeration. You may also have to keep track + * of which configuration is active when the user changes it. + * + * This function is expected to write len bytes of data into buffer, which + * is guaranteed to be big enough. If you can only do a partial write, + * return an error code. + * + * Return: + * - 0 on success + * - LIBUSB_ERROR_NOT_FOUND if the device is in unconfigured state + * - another LIBUSB_ERROR code on other failure + */ int (*get_active_config_descriptor)(struct libusb_device *device, unsigned char *buffer, size_t len); + + /* Get a specific configuration descriptor for a device. + * + * The descriptor should be retrieved from memory, NOT via bus I/O to the + * device. This means that you may have to cache it in a private structure + * during get_device_list enumeration. + * + * The requested descriptor is expressed as a zero-based index (i.e. 0 + * indicates that we are requesting the first descriptor). The index does + * not (necessarily) equal the bConfigurationValue of the configuration + * being requested. + * + * This function is expected to write len bytes of data into buffer, which + * is guaranteed to be big enough. If you can only do a partial write, + * return an error code. + * + * Return 0 on success or a LIBUSB_ERROR code on failure. + */ int (*get_config_descriptor)(struct libusb_device *device, uint8_t config_index, unsigned char *buffer, size_t len); + /* Set the active configuration for a device. + * + * A configuration value of -1 should put the device in unconfigured state. + * + * This function can block. + * + * Return: + * - 0 on success + * - LIBUSB_ERROR_NOT_FOUND if the configuration does not exist + * - LIBUSB_ERROR_BUSY if interfaces are currently claimed (and hence + * configuration cannot be changed) + * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it + * was opened + * - another LIBUSB_ERROR code on other failure. + */ int (*set_configuration)(struct libusb_device_handle *handle, int config); + /* Claim an interface. When claimed, the application can then perform + * I/O to an interface's endpoints. + * + * This function should not generate any bus I/O and should not block. + * Interface claiming is a logical operation that simply ensures that + * no other drivers/applications are using the interface, and after + * claiming, no other drivers/applicatiosn can use the interface because + * we now "own" it. + * + * Return: + * - 0 on success + * - LIBUSB_ERROR_NOT_FOUND if the interface does not exist + * - LIBUSB_ERROR_BUSY if the interface is in use by another driver/app + * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it + * was opened + * - another LIBUSB_ERROR code on other failure + */ int (*claim_interface)(struct libusb_device_handle *handle, int iface); + + /* Release a previously claimed interface. + * + * This function should also generate a SET_INTERFACE control request, + * resetting the alternate setting of that interface to 0. It's OK for + * this function to block as a result. + * + * You will only ever be asked to release an interface which was + * successfully claimed earlier. + * + * Return: + * - 0 on success + * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it + * was opened + * - another LIBUSB_ERROR code on other failure + */ int (*release_interface)(struct libusb_device_handle *handle, int iface); + /* Set the alternate setting for an interface. + * + * You will only ever be asked to set the alternate setting for an + * interface which was successfully claimed earlier. + * + * It's OK for this function to block. + * + * Return: + * - 0 on success + * - LIBUSB_ERROR_NOT_FOUND if the alternate setting does not exist + * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it + * was opened + * - another LIBUSB_ERROR code on other failure + */ int (*set_interface_altsetting)(struct libusb_device_handle *handle, int iface, int altsetting); + + /* Clear a halt/stall condition on an endpoint. + * + * It's OK for this function to block. + * + * Return: + * - 0 on success + * - LIBUSB_ERROR_NOT_FOUND if the endpoint does not exist + * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it + * was opened + * - another LIBUSB_ERROR code on other failure + */ int (*clear_halt)(struct libusb_device_handle *handle, unsigned char endpoint); + + /* Perform a USB port reset to reinitialize a device. + * + * If possible, the handle should still be usable after the reset + * completes, assuming that the device descriptors did not change during + * reset and all previous interface state can be restored. + * + * If something changes, or you cannot easily locate/verify the resetted + * device, return LIBUSB_ERROR_NOT_FOUND. This prompts the application + * to close the old handle and re-enumerate the device. + * + * Return: + * - 0 on success + * - LIBUSB_ERROR_NOT_FOUND if re-enumeration is required, or if the device + * has been disconnected since it was opened + * - another LIBUSB_ERROR code on other failure + */ int (*reset_device)(struct libusb_device_handle *handle); - /* optional */ + /* Determine if a kernel driver is active on an interface. Optional. + * + * The presence of a kernel driver on an interface indicates that any + * calls to claim_interface would fail with the LIBUSB_ERROR_BUSY code. + * + * Return: + * - 0 if no driver is active + * - 1 if a driver is active + * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it + * was opened + * - another LIBUSB_ERROR code on other failure + */ int (*kernel_driver_active)(struct libusb_device_handle *handle, int interface); + + /* Detach a kernel driver from an interface. Optional. + * + * After detaching a kernel driver, the interface should be available + * for claim. + * + * Return: + * - 0 on success + * - LIBUSB_ERROR_NOT_FOUND if no kernel driver was active + * - LIBUSB_ERROR_INVALID_PARAM if the interface does not exist + * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it + * was opened + * - another LIBUSB_ERROR code on other failure + */ int (*detach_kernel_driver)(struct libusb_device_handle *handle, int interface); + /* Destroy a device. Optional. + * + * This function is called when the last reference to a device is + * destroyed. It should free any resources allocated in the get_device_list + * path. + */ void (*destroy_device)(struct libusb_device *dev); + /* Submit a transfer. Your implementation should take the transfer, + * morph it into whatever form your platform requires, and submit it + * asynchronously. + * + * This function must not block. + * + * Return: + * - 0 on success + * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected + * - another LIBUSB_ERROR code on other failure + */ int (*submit_transfer)(struct usbi_transfer *itransfer); + + /* Cancel a previously submitted transfer. + * + * This function must not block. The transfer cancellation must complete + * later, resulting in a call to usbi_handle_transfer_cancellation() + * from the context of handle_events. + */ int (*cancel_transfer)(struct usbi_transfer *itransfer); + + /* Clear a transfer as if it has completed or cancelled, but do not + * report any completion/cancellation to the library. You should free + * all private data from the transfer as if you were just about to report + * completion or cancellation. + * + * This function might seem a bit out of place. It is used when libusb + * detects a disconnected device - it calls this function for all pending + * transfers before reporting completion (with the disconnect code) to + * the user. Maybe we can improve upon this internal interface in future. + */ void (*clear_transfer_priv)(struct usbi_transfer *itransfer); + /* Handle any pending events. This involves monitoring any active + * transfers and processing their completion or cancellation. + * + * The function is passed an array of pollfd structures (size nfds) + * as a result of the poll() system call. The num_ready parameter + * indicates the number of file descriptors that have reported events + * (i.e. the poll() return value). This should be enough information + * for you to determine which actions need to be taken on the currently + * active transfers. + * + * For any cancelled transfers, call usbi_handle_transfer_cancellation(). + * For completed transfers, call usbi_handle_transfer_completion(). + * For control/bulk/interrupt transfers, populate the "transferred" + * element of the appropriate usbi_transfer structure before calling the + * above functions. For isochronous transfers, populate the status and + * transferred fields of the iso packet descriptors of the transfer. + * + * This function should also be able to detect disconnection of the + * device, reporting that situation with usbi_handle_disconnect(). + * + * Return 0 on success, or a LIBUSB_ERROR code on failure. + */ int (*handle_events)(struct pollfd *fds, nfds_t nfds, int num_ready); - /* number of bytes to reserve for libusb_device.os_priv */ + /* Number of bytes to reserve for per-device private backend data. + * This private data area is accessible through the "os_priv" field of + * struct libusb_device. */ size_t device_priv_size; - /* number of bytes to reserve for libusb_device_handle.os_priv */ + /* Number of bytes to reserve for per-handle private backend data. + * This private data area is accessible through the "os_priv" field of + * struct libusb_device. */ size_t device_handle_priv_size; - /* number of bytes to reserve for usbi_transfer.os_priv */ + /* Number of bytes to reserve for per-transfer private backend data. + * This private data area is accessible by calling + * usbi_transfer_get_os_priv() on the appropriate usbi_transfer instance. + */ size_t transfer_priv_size; - /* number of additional bytes for os_priv for each iso packet */ + /* Mumber of additional bytes for os_priv for each iso packet. + * Can your backend use this? */ /* FIXME: linux can't use this any more. if other OS's cannot either, * then remove this */ size_t add_iso_packet_size; -- cgit v1.2.1