haiku-beta6/src/kits/storage/DiskDeviceRoster.cpp

//----------------------------------------------------------------------
//  This software is part of the OpenBeOS distribution and is covered 
//  by the OpenBeOS license.
//---------------------------------------------------------------------

#include <new.h>

#include <Directory.h>
#include <DiskDevice.h>
#include <DiskDevicePrivate.h>
#include <DiskDeviceRoster.h>
#include <DiskScannerAddOn.h>
#include <Entry.h>
#include <FindDirectory.h>
#include <Message.h>
#include <Partition.h>
#include <Path.h>
#include <RegistrarDefs.h>
#include <RosterPrivate.h>
#include <Session.h>

#include "AddOnImage.h"

//----------------------------------------------------------------------------
// Hack to make BDiskDeviceRoster communicate with our registrar.

BRoster _be_roster;
const BRoster *be_roster = &_be_roster;

// init_roster
struct _InitRoster {
	_InitRoster()
	{
		bool initialized = false;
		// find the registrar port
		port_id rosterPort = find_port(kRosterPortName);
		port_info info;
		if (rosterPort >= 0 && get_port_info(rosterPort, &info) == B_OK) {
			// construct the roster messenger
			struct {
				port_id	fPort;
				int32	fHandlerToken;
				team_id	fTeam;
				int32	extra0;
				int32	extra1;
				bool	fPreferredTarget;
				bool	extra2;
				bool	extra3;
				bool	extra4;
			} fakeMessenger;
			fakeMessenger.fPort = rosterPort;
			fakeMessenger.fHandlerToken = 0;
			fakeMessenger.fTeam = info.team;
			fakeMessenger.fPreferredTarget = true;
			BMessenger mainMessenger = *(BMessenger*)&fakeMessenger;
			// ask for the MIME messenger
			BMessage reply;
			status_t error = mainMessenger.SendMessage(
				B_REG_GET_MIME_MESSENGER, &reply);
			if (error == B_OK && reply.what == B_REG_SUCCESS) {
				BMessenger mimeMessenger;
				reply.FindMessenger("messenger", &mimeMessenger);
				BRoster::Private(_be_roster).SetTo(mainMessenger,
												   mimeMessenger);
				initialized = true;
			} else {
			}
		}
		if (!initialized) {
			printf("initializing be_roster failed!\n");
			exit(1);
		}
	}
} _InitRosterObject;

//----------------------------------------------------------------------------


/*!	\class BDiskDeviceRoster
	\brief An interface for iterating through the disk devices known to the
		   system and for a notification mechanism provided to listen to their
		   changes.
*/

/*!	\brief find_directory constants of the add-on dirs to be searched. */
static const directory_which kAddOnDirs[] = {
	B_USER_ADDONS_DIRECTORY,
//	B_COMMON_ADDONS_DIRECTORY,
	B_BEOS_ADDONS_DIRECTORY
};
/*!	\brief Size of the kAddOnDirs array. */
static const int32 kAddOnDirCount
	= sizeof(kAddOnDirs) / sizeof(directory_which);


// constructor
/*!	\brief Creates a BDiskDeviceRoster object.

	The object is ready to be used after construction.
*/
BDiskDeviceRoster::BDiskDeviceRoster()
	: fManager(),
	  fCookie(0),
	  fPartitionAddOnDir(NULL),
	  fFSAddOnDir(NULL),
	  fPartitionAddOnDirIndex(0),
	  fFSAddOnDirIndex(0)
{
	get_disk_device_messenger(&fManager);
}

// destructor
/*!	\brief Frees all resources associated with the object.
*/
BDiskDeviceRoster::~BDiskDeviceRoster()
{
	if (fPartitionAddOnDir)
		delete fPartitionAddOnDir;
	if (fFSAddOnDir)
		delete fFSAddOnDir;
}

// GetNextDevice
/*!	\brief Returns the next BDiskDevice.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized to
		   represent the next device.
	\return
	- \c B_OK: Everything went fine.
	- \c B_ENTRY_NOT_FOUND: The end of the list of devices had already been
	  reached.
	- another error code
*/
status_t
BDiskDeviceRoster::GetNextDevice(BDiskDevice *device)
{
//printf("BDiskDeviceRoster::GetNextDevice()\n");
	status_t error = (device ? B_OK : B_BAD_VALUE);
	// compose request message
	BMessage request(B_REG_NEXT_DISK_DEVICE);
	if (error == B_OK)
		error = request.AddInt32("cookie", fCookie);
	// send request
	BMessage reply;
	if (error == B_OK)
		error = fManager.SendMessage(&request, &reply);
	// analyze reply
	if (error == B_OK) {
//reply.PrintToStream();
		// result
		status_t result = B_OK;
		error = reply.FindInt32("result", &result);
//printf("  check: %s\n", strerror(error));
		if (error == B_OK)
			error = result;
//printf("  check: %s\n", strerror(error));
		// cookie
		if (error == B_OK)
			error = reply.FindInt32("cookie", &fCookie);
//printf("  check: %s\n", strerror(error));
		// device
		BMessage archive;
		if (error == B_OK)
			error = reply.FindMessage("device", &archive);
//printf("  check: %s\n", strerror(error));
		if (error == B_OK)
			error = device->_Unarchive(&archive);
//printf("  check: %s\n", strerror(error));
	}
//printf("BDiskDeviceRoster::GetNextDevice() done: %s\n", strerror(error));
	return error;
}

// Rewind
/*!	\brief Rewinds the device list iterator.
	\return \c B_OK, if everything went fine, another error code otherwise.
*/
status_t
BDiskDeviceRoster::Rewind()
{
	fCookie = 0;
	return B_OK;
}

// VisitEachDevice
/*!	\brief Iterates through the all devices.

	The supplied visitor's Visit(BDiskDevice*) is invoked for each device.
	If Visit() returns \c true, the iteration is terminated and this method
	returns \c true. If supplied, \a device is set to the concerned device.

	\param visitor The visitor.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized
		   to the device at which the iteration was terminated.
		   May be \c NULL.
	\return \c true, if the iteration was terminated, \c false otherwise.
*/
bool
BDiskDeviceRoster::VisitEachDevice(BDiskDeviceVisitor *visitor,
								   BDiskDevice *device)
{
	bool terminatedEarly = false;
	if (visitor) {
		int32 oldCookie = fCookie;
		fCookie = 0;
		BDiskDevice deviceOnStack;
		BDiskDevice *useDevice = (device ? device : &deviceOnStack);
		while (!terminatedEarly && GetNextDevice(useDevice) == B_OK)
			terminatedEarly = visitor->Visit(useDevice);
		fCookie = oldCookie;
		if (!terminatedEarly)
			useDevice->Unset();
	}
	return terminatedEarly;
}

// VisitEachSession
/*!	\brief Iterates through the all devices' sessions.

	The supplied visitor's Visit(BSession*) is invoked for each session.
	If Visit() returns \c true, the iteration is terminated and this method
	returns \c true. If supplied, \a device is set to the concerned device
	and in \a session the pointer to the session object is returned.

	\param visitor The visitor.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized
		   to the device at which the iteration was terminated.
		   May be \c NULL.
	\param session Pointer to a pre-allocated BSession pointer to be set
		   to the session at which the iteration was terminated.
		   May be \c NULL.
	\return \c true, if the iteration was terminated, \c false otherwise.
*/
bool
BDiskDeviceRoster::VisitEachSession(BDiskDeviceVisitor *visitor,
									BDiskDevice *device, BSession **session)
{
	bool terminatedEarly = false;
	if (visitor) {
		int32 oldCookie = fCookie;
		fCookie = 0;
		BDiskDevice deviceOnStack;
		BDiskDevice *useDevice = (device ? device : &deviceOnStack);
		BSession *foundSession = NULL;
		while (!foundSession && GetNextDevice(useDevice) == B_OK)
			foundSession = useDevice->VisitEachSession(visitor);
		fCookie = oldCookie;
		if (!terminatedEarly)
			useDevice->Unset();
		else if (device && session)
			*session = foundSession;
	}
	return terminatedEarly;
}

// VisitEachPartition
/*!	\brief Iterates through the all devices' partitions.

	The supplied visitor's Visit(BPartition*) is invoked for each partition.
	If Visit() returns \c true, the iteration is terminated and this method
	returns \c true. If supplied, \a device is set to the concerned device
	and in \a partition the pointer to the partition object is returned.

	\param visitor The visitor.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized
		   to the device at which the iteration was terminated.
		   May be \c NULL.
	\param partition Pointer to a pre-allocated BPartition pointer to be set
		   to the partition at which the iteration was terminated.
		   May be \c NULL.
	\return \c true, if the iteration was terminated, \c false otherwise.
*/
bool
BDiskDeviceRoster::VisitEachPartition(BDiskDeviceVisitor *visitor,
									  BDiskDevice *device,
									  BPartition **partition)
{
	bool terminatedEarly = false;
	if (visitor) {
		int32 oldCookie = fCookie;
		fCookie = 0;
		BDiskDevice deviceOnStack;
		BDiskDevice *useDevice = (device ? device : &deviceOnStack);
		BPartition *foundPartition = NULL;
		while (!foundPartition && GetNextDevice(useDevice) == B_OK)
			foundPartition = useDevice->VisitEachPartition(visitor);
		fCookie = oldCookie;
		if (!terminatedEarly)
			useDevice->Unset();
		else if (device && partition)
			*partition = foundPartition;
	}
	return terminatedEarly;
}

// Traverse
/*!	\brief Pre-order traverses the trees of the spanned by the BDiskDevices
		   and their subobjects.

	The supplied visitor's Visit() is invoked for each device, for each
	session and for each partition.
	If Visit() returns \c true, the iteration is terminated and this method
	returns \c true as well.

	\param visitor The visitor.
	\return \c true, if the iteration was terminated, \c false otherwise.
*/
bool
BDiskDeviceRoster::Traverse(BDiskDeviceVisitor *visitor)
{
	bool terminatedEarly = false;
	if (visitor) {
		int32 oldCookie = fCookie;
		fCookie = 0;
		BDiskDevice device;
		while (!terminatedEarly && GetNextDevice(&device) == B_OK)
			terminatedEarly = device.Traverse(visitor);
		fCookie = oldCookie;
	}
	return terminatedEarly;
}

// VisitEachMountedPartition
/*!	\brief Iterates through the all devices' partitions that are mounted.

	The supplied visitor's Visit(BPartition*) is invoked for each mounted
	partition.
	If Visit() returns \c true, the iteration is terminated and this method
	returns \c true. If supplied, \a device is set to the concerned device
	and in \a partition the pointer to the partition object is returned.

	\param visitor The visitor.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized
		   to the device at which the iteration was terminated.
		   May be \c NULL.
	\param partition Pointer to a pre-allocated BPartition pointer to be set
		   to the partition at which the iteration was terminated.
		   May be \c NULL.
	\return \c true, if the iteration was terminated, \c false otherwise.
*/
bool
BDiskDeviceRoster::VisitEachMountedPartition(BDiskDeviceVisitor *visitor,
											 BDiskDevice *device,
											 BPartition **partition)
{
	bool terminatedEarly = false;
	if (visitor) {
		struct MountedPartitionFilter : public PartitionFilter {
			virtual bool Filter(BPartition *partition)
				{ return partition->IsMounted(); }
		} filter;
		PartitionFilterVisitor filterVisitor(visitor, &filter);
		terminatedEarly
			= VisitEachPartition(&filterVisitor, device, partition);
	}
	return terminatedEarly;
}

// VisitEachMountablePartition
/*!	\brief Iterates through the all devices' partitions that are mountable.

	The supplied visitor's Visit(BPartition*) is invoked for each mountable
	partition.
	If Visit() returns \c true, the iteration is terminated and this method
	returns \c true. If supplied, \a device is set to the concerned device
	and in \a partition the pointer to the partition object is returned.

	\param visitor The visitor.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized
		   to the device at which the iteration was terminated.
		   May be \c NULL.
	\param partition Pointer to a pre-allocated BPartition pointer to be set
		   to the partition at which the iteration was terminated.
		   May be \c NULL.
	\return \c true, if the iteration was terminated, \c false otherwise.
*/
bool
BDiskDeviceRoster::VisitEachMountablePartition(BDiskDeviceVisitor *visitor,
											   BDiskDevice *device,
											   BPartition **partition)
{
	bool terminatedEarly = false;
	if (visitor) {
		struct MountablePartitionFilter : public PartitionFilter {
			virtual bool Filter(BPartition *partition)
				{ return partition->ContainsFileSystem(); }
		} filter;
		PartitionFilterVisitor filterVisitor(visitor, &filter);
		terminatedEarly
			= VisitEachPartition(&filterVisitor, device, partition);
	}
	return terminatedEarly;
}

// VisitEachInitializablePartition
/*!	\brief Iterates through the all devices' partitions that are initializable.

	The supplied visitor's Visit(BPartition*) is invoked for each
	initializable partition.
	If Visit() returns \c true, the iteration is terminated and this method
	returns \c true. If supplied, \a device is set to the concerned device
	and in \a partition the pointer to the partition object is returned.

	\param visitor The visitor.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized
		   to the device at which the iteration was terminated.
		   May be \c NULL.
	\param partition Pointer to a pre-allocated BPartition pointer to be set
		   to the partition at which the iteration was terminated.
		   May be \c NULL.
	\return \c true, if the iteration was terminated, \c false otherwise.
*/
bool
BDiskDeviceRoster::VisitEachInitializablePartition(BDiskDeviceVisitor *visitor,
												   BDiskDevice *device,
												   BPartition **partition)
{
	bool terminatedEarly = false;
	if (visitor) {
		struct InitializablePartitionFilter : public PartitionFilter {
			virtual bool Filter(BPartition *partition)
				{ return !partition->IsHidden(); }
		} filter;
		PartitionFilterVisitor filterVisitor(visitor, &filter);
		terminatedEarly
			= VisitEachPartition(&filterVisitor, device, partition);
	}
	return terminatedEarly;
}

// GetDeviceWithID
/*!	\brief Returns a BDiskDevice for a given ID.

	The supplied \a device is initialized to the device identified by \a id.

	\param id The ID of the device to be retrieved.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized
		   to the device identified by \a id.
	\return
	- \c B_OK: Everything went fine.
	- \c B_ENTRY_NOT_FOUND: A device with ID \a id could not be found.
	- other error codes
*/
status_t
BDiskDeviceRoster::GetDeviceWithID(int32 id, BDiskDevice *device) const
{
	return _GetObjectWithID("device_id", id, device);
}

// GetSessionWithID
/*!	\brief Returns a BSession for a given ID.

	The supplied \a device is initialized to the device the session identified
	by \a id resides on, and \a session is set to point to the respective
	BSession.

	\param id The ID of the session to be retrieved.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized
		   to the device the session identified by \a id resides on.
	\param session Pointer to a pre-allocated BSession pointer to be set to
		   the session identified by \a id.
	\return
	- \c B_OK: Everything went fine.
	- \c B_ENTRY_NOT_FOUND: A session with ID \a id could not be found.
	- other error codes
*/
status_t
BDiskDeviceRoster::GetSessionWithID(int32 id, BDiskDevice *device,
									BSession **session) const
{
	status_t error = (device && session ? B_OK : B_BAD_VALUE);
	if (error == B_OK)
		error = _GetObjectWithID("session_id", id, device);
	if (error == B_OK)
		*session = device->SessionWithID(id);
	return error;
}

// GetPartitionWithID
/*!	\brief Returns a BPartition for a given ID.

	The supplied \a device is initialized to the device the partition
	identified by \a id resides on, and \a partition is set to point to the
	respective BPartition.

	\param id The ID of the partition to be retrieved.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized
		   to the device the partition identified by \a id resides on.
	\param partition Pointer to a pre-allocated BPartition pointer to be set
		   to the partition identified by \a id.
	\return
	- \c B_OK: Everything went fine.
	- \c B_ENTRY_NOT_FOUND: A partition with ID \a id could not be found.
	- other error codes
*/
status_t
BDiskDeviceRoster::GetPartitionWithID(int32 id, BDiskDevice *device,
									  BPartition **partition) const
{
	status_t error = (device && partition ? B_OK : B_BAD_VALUE);
	if (error == B_OK)
		error = _GetObjectWithID("partition_id", id, device);
	if (error == B_OK)
		*partition = device->PartitionWithID(id);
	return error;
}

// StartWatching
/*!	\brief Adds a target to the list of targets to be notified on disk device
		   events.

	\todo List the event mask flags, the events and describe the layout of the
		  notification message.

	If \a target is already listening to events, this method replaces the
	former event mask with \a eventMask.

	\param target A BMessenger identifying the target to which the events
		   shall be sent.
	\param eventMask A mask specifying on which events the target shall be
		   notified.
	\return \c B_OK, if everything went fine, another error code otherwise.
*/
status_t
BDiskDeviceRoster::StartWatching(BMessenger target, uint32 eventMask)
{
	status_t error = B_OK;
	// compose request message
	BMessage request(B_REG_DEVICE_START_WATCHING);
	if (error == B_OK)
		error = request.AddMessenger("target", target);
	if (error == B_OK)
		error = request.AddInt32("events", (int32)eventMask);
	// send request
	BMessage reply;
	if (error == B_OK)
		error = fManager.SendMessage(&request, &reply);
	// analyze reply
	if (error == B_OK) {
		// result
		status_t result = B_OK;
		error = reply.FindInt32("result", &result);
		if (error == B_OK)
			error = result;
	}
	return error;
}

// StopWatching
/*!	\brief Remove a target from the list of targets to be notified on disk
		   device events.
	\param target A BMessenger identifying the target to which notfication
		   message shall not longer be sent.
	\return \c B_OK, if everything went fine, another error code otherwise.
*/
status_t
BDiskDeviceRoster::StopWatching(BMessenger target)
{
	status_t error = B_OK;
	// compose request message
	BMessage request(B_REG_DEVICE_STOP_WATCHING);
	if (error == B_OK)
		error = request.AddMessenger("target", target);
	// send request
	BMessage reply;
	if (error == B_OK)
		error = fManager.SendMessage(&request, &reply);
	// analyze reply
	if (error == B_OK) {
		// result
		status_t result = B_OK;
		error = reply.FindInt32("result", &result);
		if (error == B_OK)
			error = result;
	}
	return error;
}

// GetNextPartitioningSystem
/*!	\brief Returns the next partitioning system capable of partitioning.

	The returned \a shortName can be passed to BSession::Partition().

	\param shortName Pointer to a pre-allocation char buffer, of size
		   \c B_FILE_NAME_LENGTH or larger into which the short name of the
		   partitioning system shall be written.
	\param longName Pointer to a pre-allocation char buffer, of size
		   \c B_FILE_NAME_LENGTH or larger into which the long name of the
		   partitioning system shall be written. May be \c NULL.
	\return
	- \c B_OK: Everything went fine.
	- \c B_BAD_VALUE: \c NULL \a shortName.
	- \c B_ENTRY_NOT_FOUND: End of the list has been reached.
	- other error codes
*/
status_t
BDiskDeviceRoster::GetNextPartitioningSystem(char *shortName, char *longName)
{
	status_t error = (shortName ? B_OK : B_BAD_VALUE);
	if (error == B_OK) {
		// search until an add-on has been found or the end of all directories
		// has been reached
		bool found = false;
		do {
			// get the next add-on in the current dir
			AddOnImage image;
			error = _GetNextAddOn(fPartitionAddOnDir, &image);
			if (error == B_OK) {
				// add-on loaded: get the function that creates an add-on
				// object
				BDiskScannerPartitionAddOn *(*create_add_on)();
				if (get_image_symbol(image.ID(), "create_ds_partition_add_on",
									 B_SYMBOL_TYPE_TEXT,
									 (void**)&create_add_on) == B_OK) {
					// create the add-on object and copy the requested data
					if (BDiskScannerPartitionAddOn *addOn
						= (*create_add_on)()) {
						const char *addOnShortName = addOn->ShortName();
						const char *addOnLongName = addOn->LongName();
						if (addOnShortName && addOnLongName) {
							strcpy(shortName, addOnShortName);
							if (longName)
								strcpy(longName, addOnLongName);
							found = true;
						}
						delete addOn;
					}
				}
			} else if (error == B_ENTRY_NOT_FOUND) {
				// end of the current directory has been reached, try next dir
				error = _GetNextAddOnDir(&fPartitionAddOnDir,
										 &fPartitionAddOnDirIndex,
										 "partition");
			}
		} while (error == B_OK && !found);
	}
	return error;
}

// GetNextFileSystem
/*!	\brief Returns the next file system capable of initializing.

	The returned \a shortName can be passed to BPartition::Initialize().

	\param shortName Pointer to a pre-allocation char buffer, of size
		   \c B_FILE_NAME_LENGTH or larger into which the short name of the
		   file system shall be written.
	\param longName Pointer to a pre-allocation char buffer, of size
		   \c B_FILE_NAME_LENGTH or larger into which the long name of the
		   file system shall be written. May be \c NULL.
	\return
	- \c B_OK: Everything went fine.
	- \c B_BAD_VALUE: \c NULL \a shortName.
	- \c B_ENTRY_NOT_FOUND: End of the list has been reached.
	- other error codes
*/
status_t
BDiskDeviceRoster::GetNextFileSystem(char *shortName, char *longName)
{
	status_t error = (shortName ? B_OK : B_BAD_VALUE);
	if (error == B_OK) {
		// search until an add-on has been found or the end of all directories
		// has been reached
		bool found = false;
		do {
			// get the next add-on in the current dir
			AddOnImage image;
			error = _GetNextAddOn(fFSAddOnDir, &image);
			if (error == B_OK) {
				// add-on loaded: get the function that creates an add-on
				// object
				BDiskScannerFSAddOn *(*create_add_on)();
				if (get_image_symbol(image.ID(), "create_ds_fs_add_on",
									 B_SYMBOL_TYPE_TEXT,
									 (void**)&create_add_on) == B_OK) {
					// create the add-on object and copy the requested data
					if (BDiskScannerFSAddOn *addOn = (*create_add_on)()) {
						const char *addOnShortName = addOn->ShortName();
						const char *addOnLongName = addOn->LongName();
						if (addOnShortName && addOnLongName) {
							strcpy(shortName, addOnShortName);
							if (longName)
								strcpy(longName, addOnLongName);
							found = true;
						}
						delete addOn;
					}
				}
			} else if (error == B_ENTRY_NOT_FOUND) {
				// end of the current directory has been reached, try next dir
				error = _GetNextAddOnDir(&fFSAddOnDir, &fFSAddOnDirIndex,
										 "fs");
			}
		} while (error == B_OK && !found);
	}
	return error;
}

// RewindPartitiningSystems
/*!	\brief Rewinds the partitioning system list iterator.
	\return \c B_OK, if everything went fine, another error code otherwise.
*/
status_t
BDiskDeviceRoster::RewindPartitiningSystems()
{
	if (fPartitionAddOnDir) {
		delete fPartitionAddOnDir;
		fPartitionAddOnDir = NULL;
	}
	fPartitionAddOnDirIndex = 0;
	return B_OK;
}

// RewindFileSystems
/*!	\brief Rewinds the file system list iterator.
	\return \c B_OK, if everything went fine, another error code otherwise.
*/
status_t
BDiskDeviceRoster::RewindFileSystems()
{
	if (fFSAddOnDir) {
		delete fFSAddOnDir;
		fFSAddOnDir = NULL;
	}
	fFSAddOnDirIndex = 0;
	return B_OK;
}

// _GetObjectWithID
/*!	\brief Returns a BDiskDevice for a given device, session or partition ID.

	The supplied \a device is initialized to the device the object identified
	by \a id belongs to.

	\param fieldName "device_id", "sesison_id" or "partition_id" according to
		   the type of object the device shall be retrieved for.
	\param id The ID of the device, session or partition to be retrieved.
	\param device Pointer to a pre-allocated BDiskDevice to be initialized
		   to the device to be retrieved.
	\return
	- \c B_OK: Everything went fine.
	- \c B_ENTRY_NOT_FOUND: A device, session or partition respectively with
		 ID \a id could not be found.
	- other error codes
*/
status_t
BDiskDeviceRoster::_GetObjectWithID(const char *fieldName, int32 id,
									BDiskDevice *device) const
{
	status_t error = (device ? B_OK : B_BAD_VALUE);
	// compose request message
	BMessage request(B_REG_GET_DISK_DEVICE);
	if (error == B_OK)
		error = request.AddInt32(fieldName, id);
	// send request
	BMessage reply;
	if (error == B_OK)
		error = fManager.SendMessage(&request, &reply);
	// analyze reply
	if (error == B_OK) {
		// result
		status_t result = B_OK;
		error = reply.FindInt32("result", &result);
		if (error == B_OK)
			error = result;
		// device
		BMessage archive;
		if (error == B_OK)
			error = reply.FindMessage("device", &archive);
		if (error == B_OK)
			error = device->_Unarchive(&archive);
	}
	return error;
}


// _GetNextAddOn
/*!	\brief Finds and loads the next add-on of an add-on subdirectory.
	\param directory The add-on directory.
	\param image Pointer to an image_id into which the image ID of the loaded
		   add-on shall be written.
	\return
	- \c B_OK: Everything went fine.
	- \c B_ENTRY_NOT_FOUND: End of directory.
	- other error codes
*/
status_t
BDiskDeviceRoster::_GetNextAddOn(BDirectory **directory, int32 *index,
								 const char *subdir, AddOnImage *image)
{
	status_t error = (directory && index && subdir && image
					  ? B_OK : B_BAD_VALUE);
	if (error == B_OK) {
		// search until an add-on has been found or the end of all directories
		// has been reached
		bool found = false;
		do {
			// get the next add-on in the current dir
			error = _GetNextAddOn(*directory, image);
			if (error == B_OK) {
				found = true;
			} else if (error == B_ENTRY_NOT_FOUND) {
				// end of the current directory has been reached, try next dir
				error = _GetNextAddOnDir(directory, index, subdir);
			}
		} while (error == B_OK && !found);
	}
	return error;
}

// _GetNextAddOn
/*!	\brief Finds and loads the next add-on of an add-on subdirectory.
	\param directory The add-on directory.
	\param image Pointer to an image_id into which the image ID of the loaded
		   add-on shall be written.
	\return
	- \c B_OK: Everything went fine.
	- \c B_ENTRY_NOT_FOUND: End of directory.
	- other error codes
*/
status_t
BDiskDeviceRoster::_GetNextAddOn(BDirectory *directory, AddOnImage *image)
{
	status_t error = (directory ? B_OK : B_ENTRY_NOT_FOUND);
	if (error == B_OK) {
		// iterate through the entry list and try to load the entries
		bool found = false;
		while (error == B_OK && !found) {
			BEntry entry;
			error = directory->GetNextEntry(&entry);
			BPath path;
			if (error == B_OK && entry.GetPath(&path) == B_OK)
				found = (image->Load(path.Path()) == B_OK);
		}
	}
	return error;
}

// _GetNextAddOnDir
/*!	\brief Gets the next add-on directory path.
	\param path Pointer to a BPath to be set to the found directory.
	\param index Pointer to an index into the kAddOnDirs array indicating
		   which add-on dir shall be retrieved next.
	\param subdir Name of the subdirectory (in the "disk_scanner" subdirectory
		   of the add-on directory) \a directory shall be set to.
	\return
	- \c B_OK: Everything went fine.
	- \c B_ENTRY_NOT_FOUND: End of directory list.
	- other error codes
*/
status_t
BDiskDeviceRoster::_GetNextAddOnDir(BPath *path, int32 *index,
									const char *subdir)
{
	status_t error = (*index < kAddOnDirCount ? B_OK : B_ENTRY_NOT_FOUND);
	// get the add-on dir path
	if (error == B_OK) {
		error = find_directory(kAddOnDirs[*index], path);
		(*index)++;
	}
	// construct the subdirectory path
	if (error == B_OK) {
		error = path->Append("disk_scanner");
		if (error == B_OK)
			error = path->Append(subdir);
	}
if (error == B_OK)
printf("  next add-on dir: `%s'\n", path->Path());
	return error;
}

// _GetNextAddOnDir
/*!	\brief Gets the next add-on directory.
	\param directory Pointer to a BDirectory* to be set to the found directory.
	\param index Pointer to an index into the kAddOnDirs array indicating
		   which add-on dir shall be retrieved next.
	\param subdir Name of the subdirectory (in the "disk_scanner" subdirectory
		   of the add-on directory) \a directory shall be set to.
	\return
	- \c B_OK: Everything went fine.
	- \c B_ENTRY_NOT_FOUND: End of directory list.
	- other error codes
*/
status_t
BDiskDeviceRoster::_GetNextAddOnDir(BDirectory **directory, int32 *index,
									const char *subdir)
{
	BPath path;
	status_t error = _GetNextAddOnDir(&path, index, subdir);
	// create a BDirectory object, if there is none yet.
	if (error == B_OK && !*directory) {
		*directory = new BDirectory;
		if (!*directory)
			error = B_NO_MEMORY;
	}
	// init the directory
	if (error == B_OK)
		error = (*directory)->SetTo(path.Path());
	// cleanup on error
	if (error != B_OK && *directory) {
		delete *directory;
		*directory = NULL;
	}
	return error;
}

// _LoadPartitionAddOn
status_t
BDiskDeviceRoster::_LoadPartitionAddOn(const char *partitioningSystem,
									   AddOnImage *image,
									   BDiskScannerPartitionAddOn **_addOn)
{
	status_t error = (partitioningSystem && image && _addOn
		? B_OK : B_BAD_VALUE);
	// load the image
	bool found = false;
	BPath path;
	BDirectory *directory = NULL;
	int32 index = 0;
	while (error == B_OK && !found) {
		error = _GetNextAddOn(&directory, &index, "partition", image);
		if (error == B_OK) {
			// add-on loaded: get the function that creates an add-on
			// object
			BDiskScannerPartitionAddOn *(*create_add_on)();
			if (get_image_symbol(image->ID(), "create_ds_partition_add_on",
								 B_SYMBOL_TYPE_TEXT,
								 (void**)&create_add_on) == B_OK) {
				// create the add-on object and copy the requested data
				if (BDiskScannerPartitionAddOn *addOn = (*create_add_on)()) {
					if (!strcmp(addOn->ShortName(), partitioningSystem)) {
						*_addOn = addOn;
						found = true;
					} else
						delete addOn;
				}
			}
		}
	}
	// cleanup
	if (directory)
		delete directory;
	if (error != B_OK && image)
		image->Unload();
	return error;
}