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This file contains the documentation written by Thomas Kurschel that was originally found in the headers of his pnp_manager. It’s outdated but could be used as a basis for the real documentation.
PnP manager; Takes care of registration and loading of PnP drivers
Read pnp_driver.h first to understand the basic idea behind PnP drivers.
To register a driver node, use register_driver. If the device got lost, use unregister_driver (note: if the parent node is removed, your node get removed automatically as your driver has obviously nothing to work with anymore). To get access to a (parent) device, use load_driver/ unload_driver.
To let the manager find a consumer (see pnp_driver.h), you can either specify its name directly during registration, using a PNP_DRIVER_FIXED_CONSUMER attribute, or let the manager search the appropriate consumer(s) via a PNP_DRIVER_DYNAMIC_CONSUMER attribute.
Searching of dynamic consumers is done as follows:
Specification of the base directory and of the names of Specific drivers is done via a file name pattern given by a PNP_DRIVER_DYNAMIC_CONSUMER attribute.
First, all substrings of the form “%attribute_name%” are replaced by the content of the attribute “attribute_name” as follows:
Second, the resulting name is split into chunks according to the presence of | characters (you can escape % and | with a ^ character). These characters are only delimiters and get removed before further processing. The directory before the first | character is the base directory (see above). It contains the “generic” and the “universal” subdirectories. The names of the specific drivers are created by first taking the entire file name, then by removing the last chunk, then by removing the last two chunks and so on until only the first chunk is left.
As drivers can contain multiple modules, the module name is constructed by appending the content of the PNP_DRIVER_TYPE attribute to the driver’s file name, seperated by a slash character (note: this only applies to dynamic consumers; for fixed consumers, you specify the module name directly via PNP_DRIVER_FIXED_CONSUMER).
E.g. given a dynamic consumer pattern of “pci/vendor=%vendor_id%|, device=%device_id%” for a device with the attributes vendor_id=0x123 and device_id=0xabcd (both being uint16), the PnP manager tries the specific drivers “pci/vendor=0123, device=abcd” and (if the first one fails/doesn’t exist) “pci/vendor=0123”. If they both refuse to handle the device, all drivers under “pci/generic” are tried until one accepts the device. Finally, all drivers under “pci/universal” are loaded, whatever happened before.
In practise, you should try to use specific drivers as much as possible. If detection based on device IDs is impossible (e.g. because the bus doesn’t support them at all), you can put the driver under “generic”. Generic drivers can also be used to specify wrappers that try to load old- style drivers if no new driver can be found. Also, they can be used to report an error or invoke an user program that tries downloading a proper Specific driver. Universal drivers are mainly used for informational purposes, e.g. to publish data about each found device, or to provide raw access to all devices.
If the device uses physical address space or I/O space or ISA DMA channels (called I/O resources), the driver has to acquire these resources. During hardware detection (usually via probe()), acquire_io_resources() must be called to get exclusive access. If no hardware could be found, they must be released via release_io_resources(). If detection was successful, the list of the (acquired) resources must be passed to register_device(). Resources can either belong to one hardware detection or to a device. If a hardware detection collides with another, it has to wait; if it collides with a device whose driver is not loaded, the driver loading is blocked. When detection fails, i.e. if release_io_resources() is called, all blocked drivers can be loaded again. If the detection fails, i.e. the resources are transferred via register_device(), all blocked devices are unregistered and pending load requests aborted. If a hardware detection collides with a device whose driver is loaded, acquire_io_resources() fails with B_BUSY. As this makes a hardware rescan impossible if the driver is loaded, you should define PNP_DRIVER_NO_LIVE_RESCAN for nodes that use I/O resources (see below).
To search for new drivers for a given device node, use rescan(). This marks all consumer devices as being verified and calls probe() of all consumers drivers (see above) to let them rescan the parent for devices. The <depth> parameter determines the nesting level, e.g. 2 means that first the consumers are scanned and then the consumers of the consumers.
Normally, all devices can be rescanned. If a driver cannot handle a rescan safely when it is loaded (i.e. used by a consumer), it must set PNP_DRIVER_NO_LIVE_RESCAN, in which case the device is ignored during rescan if the driver is loaded and attempts to load the driver during a rescan are blocked until the rescan is finished. If rescanning a device is not possible at all, it must have set PNP_DRIVER_NEVER_RESCAN to always ignore it.
To distinguish between new devices, lost devices and redetected devices, consumer devices should provide a connection code and a device identifier. They are specified by PNP_DRIVER_CONNECTION and PNP_DRIVER_CONNECTION respectively, and are expanded in the same way as PNP_DRIVER_DYNAMIC_CONSUMER. It is assumed that there can be only one device per connection and that a device can be uniquely identify by a device identifier. If a consumer device is registered on the same connection as an existing device but with a different device identifier, the old device gets unregistered automatically. If both connection and device identifier are the same, registration is handled as a redetection and ignored (unless a different type or driver module is specified - in this case, the device is replaced). Devices that were not redetected during a rescan get unregistered unless they were ignored (see above).
// interface of PnP manager
typedef struct device_manager_info {
module_info info;
// load driver
// node - node whos driver is to be loaded
// user_cookie - cookie to be passed to init_device of driver
// interface - interface of loaded driver
// cookie - device cookie issued by loaded driver
status_t (*init_driver)(device_node_handle node, void *userCookie,
driver_module_info **interface, void **cookie);
// unload driver
status_t (*uninit_driver)(device_node_handle node);
// rescan node for new dynamic drivers
// node - node whose dynamic drivers are to be scanned
status_t (*rescan)(device_node_handle node);
// register device
// parent - parent node
// attributes - NULL-terminated array of node attributes
// io_resources - NULL-terminated array of I/O resources (can be NULL)
// node - new node handle
// on return, io_resources are invalid: on success I/O resources belong
// to node, on fail they are released;
// if device is already registered, B_OK is returned but *node is NULL
status_t (*register_device)(device_node_handle parent,
const device_attr *attrs,
const io_resource_handle *io_resources,
device_node_handle *node);
// unregister device
// all nodes having this node as their parent are unregistered too.
// if the node contains PNP_MANAGER_ID_GENERATOR/PNP_MANAGER_AUTO_ID
// pairs, the id specified this way is freed too
status_t (*unregister_device)(device_node_handle node);
// find device by node content
// the given attributes must _uniquely_ identify a device node;
// parent - parent node (-1 for don't-care)
// attrs - list of attributes (can be NULL)
// The node you got will be automatically put on the next call
// to this function.
status_t (*get_next_child_device)(device_node_handle parent,
device_node_handle *_node, const device_attr *attrs);
// get parent device node
device_node_handle (*get_parent)(device_node_handle node);
// Must be called after get_next_child_device() (if you don't iterate through)
// and get_parent() to make sure the node is freed when it's not used anymore
void (*put_device_node)(device_node_handle node);
// acquire I/O resources
// resources - NULL-terminated array of resources to acquire
// handles - NULL-terminated array of handles (one per resource);
// array must be provided by caller
// return B_BUSY if a resource is used by a loaded driver
status_t (*acquire_io_resources)(io_resource *resources,
io_resource_handle *handles);
// release I/O resources
// handles - NULL-terminated array of handles
status_t (*release_io_resources)(const io_resource_handle *handles);
// create unique id
// generator - name of id set
// if result >= 0 - unique id
// result < 0 - error code
int32 (*create_id)(const char *generator);
// free unique id
status_t (*free_id)(const char *generator, uint32 id);
// helpers to extract attribute by name.
// if <recursive> is true, parent nodes are scanned if
// attribute isn't found in current node; unless you declared
// the attribute yourself, use recursive search to handle
// intermittent nodes, e.g. defined by filter drivers, transparently.
// for raw and string attributes, you get a copy that must
// be freed by caller
status_t (*get_attr_uint8)(device_node_handle node,
const char *name, uint8 *value, bool recursive);
status_t (*get_attr_uint16)(device_node_handle node,
const char *name, uint16 *value, bool recursive);
status_t (*get_attr_uint32)(device_node_handle node,
const char *name, uint32 *value, bool recursive);
status_t (*get_attr_uint64)(device_node_handle node,
const char *name, uint64 *value, bool recursive);
status_t (*get_attr_string)(device_node_handle node,
const char *name, char **value, bool recursive);
status_t (*get_attr_raw)(device_node_handle node,
const char *name, void **data, size_t *_size,
bool recursive);
// get next attribute of node;
// on call, *<attr_handle> must contain handle of an attribute;
// on return, *<attr_handle> is replaced by the next attribute or
// NULL if it was the last;
// to get the first attribute, <attr_handle> must point to NULL;
// the returned handle must be released by either passing it to
// another get_next_attr() call or by using release_attr()
// directly
status_t (*get_next_attr)(device_node_handle node,
device_attr_handle *attrHandle);
// release attribute handle <attr_handle> of <node>;
// see get_next_attr
status_t (*release_attr)(device_node_handle node,
device_attr_handle attr_handle);
// retrieve attribute data with handle given;
// <attr> is only valid as long as you don't release <attr_handle>
// implicitely or explicitely
status_t (*retrieve_attr)(device_attr_handle attr_handle,
const device_attr **attr);
// change/add attribute <attr> of/to node
status_t (*write_attr)(device_node_handle node,
const device_attr *attr);
// remove attribute of node by name
// <name> is name of attribute
status_t (*remove_attr)(device_node_handle node, const char *name);
} device_manager_info;
Required interface of PnP drivers
In contrast to standard BeOS drivers, PnP drivers are normal modules having the interface described below.
Every device is described by its driver via a PnP node with properties described in PnP Node Attributes. Devices are organized in a hierarchy, e.g. a devfs device is a hard disk device that is connected to a controller, which is a PCI device, that is connected to a PCI bus. Every device is connected to its lower-level device via a parent link stored in its Node. The higher-level is called the consumer of the lower-level device. If the lower-level device gets removed, all its consumers are removed too.
In our example, the hierarchy is
devfs device -> hard disk -> controller -> PCI device -> PCI bus
If the PCI bus is removed, everything up to including the devfs device is removed too.
The driver hierarchy is constructed bottom-up, i.e. the lower-level driver searches for a corresponding consumer, which in turns searches for its consumer and so on. The lowest driver is usually something like a PCI bus, the highest driver is normally a devfs entry (see pnp_devfs.h). Registration of devices and the search for appropriate consumers is done via the pnp_manager (see pnp_manager.h).
When a potential consumer is found, it gets informed about the new lower-level device and can either refuse its handling or accept it. On accept, it has to create a new node with the lower-level device node as its parent.
Loading of drivers is done on demand, i.e. if the consumer wants to access its lower-level device, it explicitely loads the corresponding driver, and once it doesn’t need it anymore, the lower-level driver must be unloaded. Usually, this process happens recursively, i.e. in our example, the hard disk driver loads the controller driver, which loads the PCI device driver which loads the PCI bus driver. The same process applies to unloading.
Because of this dynamic loading, drivers must store persistent data in the node of their devices. Please be aware that you cannot modify a node once published.
If a device gets removed, you must unregister its node. As said, the PnP manager will automatically unregister all consumers too. The corresponding drivers are notified to stop talking to their lower-level devices and to terminate running requests. Normally, you want to use a dedicated variable that is verified at each call to make sure that the parent is still there. The notification is done independantly of the driver being loaded by its consumer(s) or not. If it isn’t loaded, the notification callback gets NULL as the device cookie; normally, the driver returns immediately in this case. As soon as both the device is removed and the driver is unloaded, device_cleanup gets called to free resources that couldn’t be safely removed in device_removed when the driver was still loaded.
If a device has exactly one consumer, they often interact in some way. To simplify that, the consumer can pass a user-cookie to its parent during load. In this case, it’s up to the parent driver to get a pointer to the interface of the consumer. Effectively, such consumers have one interface for their consumers (base on pnp_driver_info), and a another for their parents (with a completely driver-specific structure).
In terms of synchronization, loading/unloading/remove-notifications are executed synchronously, i.e. if e.g. a device is to be unloaded but the drive currently handles a remove-notification, the unloading is delayed until the nofication callback returns. If multiple consumers load a driver, the driver gets initialized only once; subsequent load requests increase an internal load count only and return immediately. In turn, unloading only happens once the load count reaches zero.
struct driver_module_info {
module_info info;
float (*supports_device)(device_node_handle parent, bool *_noConnection);
// check whether this parent is supported
status_t (*register_device)(device_node_handle parent);
// Register your device node.
status_t (*init_driver)(device_node_handle node, void *user_cookie, void **_cookie);
// driver is loaded.
// node - node of device
// user_cookie - cookie passed by loading driver
// cookie - cookie issued by this driver
status_t (*uninit_driver)(void *cookie);
// driver gets unloaded.
void (*device_removed)(device_node_handle node, void *cookie);
// a device node, registered by this driver, got removed.
// if the driver wasn't loaded when this happenes, no (un)init_device
// is called and thus <cookie> is NULL;
void (*device_cleanup)(device_node_handle node);
// a device node, registered by this driver, got removed and
// the driver got unloaded
void (*get_supported_paths)(const char ***_busses, const char ***_devices);
};
Required interface of PnP bus drivers
Busses consist of two node layers: the lower layer defines the bus, the upper layer defines the abstract devices connected to the bus. Both layers are handled by a bus manager. Actual device nodes are on top of abstract device nodes.
E.g. if we have a PCI bus with an IDE controller on it, we get
IDE controller -> PCI device -> PCI bus
with:
The PCI bus manager establishes both the PCI devices and the PCI busses.
Abstract device nodes act as a gateway between actual device nodes and the corresponding bus node. They are constructed by the bus node driver via its rescan() hook. To identify a bus node, define PNP_BUS_IS_BUS as an attribute of it. As a result, the PnP manager will call the rescan() method of the bus driver whenever the bus is to be rescanned. Afterwards, all possible dynamic consumers are informed as done for normal nodes.
Normally, potential device drivers are notified immediately when rescan() registers a new abstract device node. But sometimes, device drivers need to know _all_ devices connected to the bus for correct detection. To ensure this, the bus node must define PNP_BUS_NOTIFY_CONSUMERS_AFTER_RESCAN. In this case, scanning for consumers is postponed until rescan() has finished.
If hot-plugging of devices can be detected automatically (e.g. USB), you should define PNP_DRIVER_ALWAYS_LOADED, so the bus driver is always loaded and thus capable of handling hot-plug events generated by the bus controller hardware.