The Storage Kit: BVolumeRoster

Derived from: (none)

Declared in: be/nustorage/VolumeRoster.h

Library: libbe.so

Overview

The BVolumeRoster class keeps track of the volumes thatare mounted in the file system hierarchy. It lets you know about volumes in two ways:

		It lists the volumes that are currently mounted. You can step through the list through iterative calls to the GetNextVolume() function.
		It lets you know when new volumes are mounted, and when existing volumes are unmounted. (See StartWatching().)

How you create your BVolumeRoster object depends on what you're going to do with it:

If you simply want to step through the volume list, then creating a BVolumeRoster on the stack is acceptable and sufficient.

However, if you want to watch for volumes being mounted and unmounted, then you must keep your BVolumeRoster object around. The watching stops when the object is deleted.

A single BVolumeRoster object can perform both functions: You can use it to step through the volume list at the same time that it's watching volumes.

Constructor and Destructor

BVolumeRoster()

      BVolumeRoster(void)

Creates a new BVolumeRoster object. You don't have to "initialize" the object before using it (as you do with most other Storage Kit classes). You can call GetNextVolume() (or whatever) immediately after constructing.

~BVolumeRoster()

      ~BVolumeRoster(void)

Destroys the object. If this BVolumeRoster object was watching volumes, the watch is called off.

Member Functions

GetBootVolume()

      status_t GetBootVolume(BVolume *boot_vol)

Initializes boot_vol to refer to the "boot volume." This is the volume that was used to boot the computer. boot_vol must be allocated before you pass it in. If the boot volume can't be found, the argument is uninitialized.

(Currently, this function looks for the volume that's mounted at /boot. The only way to fool the system into thinking that there isn't a boot volume is to rename /boot--not a smart thing to do.)

RETURN CODES

• B_NO_ERROR. The boot volume was successfully retrieved.
• B_ENTRY_NOT_FOUND. The boot volume wasn't found.

GetNextVolume(), Rewind()

      status_t GetNextVolume(BVolume *volume)
      void Rewind(void) 

GetNextVolume() retrieves the "next" volume from the volume list and uses it to initialize the argument (which must be allocated). When the function return B_BAD_VALUE, you've reached the end of the list.

Rewind() rewinds the volume list such that the next GetNextVolume() will return the first element in the list.

RETURN CODES

• B_NO_ERROR. The next volume was successfully retrieved.
• B_BAD_VALUE. You've reached the end of the volume list.

StartWatching(), StopWatching(), Messenger()

      status_t StartWatching(BMessenger messenger = be_app_messenger)
      status_t StopWatching(void)
      BMessenger Messenger(void) const

These functions start and stop the BVolumeRoster's volume-watching facility. (This is actually just a convenient cover for the Node Monitor.)

• StartWatching() registers a request for notifications of volume mounts and unmounts . The notifications are sent (as BMessages) to the BHandler/BLooper pair specified by the argument. There are separate messages for mounting and unmounting; their formats are described below. The caller retains possession of the BHandler/BLooper that the BMessenger represents. The volume watching continues until this BVolumeRoster object is destroyed, or until you call...

• StopWatching(). This function tells the volume-watcher to stop watching. In other words, notifications of volume mounts and unmounts are no longer sent to the BVolumeRoster's target.

• Messenger() returns a copy of the BMessenger object that was set in the previous StartWatching() call.

There are separate notifications (BMessages) for volume-mounted and volume-unmounted. The fields are...

Volume Mounted

• what is B_DEVICE_MOUNTED.

• "new device" (B_INT32_TYPE). The dev_t number of the newly-mounted device.

• "device" (B_INT32_TYPE). The dev_t number of the device that holds the directory of the new device's mount point.

• "directory" (B_INT64_TYPE). The ino_t number of the directory that acts as the new device's mount point.

Volume Unmounted

• what is B_DEVICE_UNMOUNTED.

• "device" (B_INT32_TYPE). The dev_t number of the device that was just unmounted. Be careful with this number; dev_ts are quickly recycled. You should only need this number if you're keeping a list of the dev_ts of all mounted disks and you want to remove the dev_t for this recently-unmounted volume (keeping in mind that a device mounted message bearing this dev_t may arrive in the meantime).

RETURN CODES

• B_NO_ERROR. The volume-watcher was successfully started or stopped.
• B_BAD_VALUE. Poorly formed BMessenger.
• B_NO_MEMORY. Couldn't allocate resources.

The Be Book, in lovely HTML, for the BeOS Preview Release.

Copyright © 1997 Be, Inc. All rights reserved.

Be is a registered trademark; BeOS, BeBox, BeWare, GeekPort, the Be logo, and the BeOS logo are trademarks of Be, Inc.

Last modified July 17, 1997.