BVolume¶

The BVolume class lets you ask questions about specific “volumes,” where a volume is any independent file system. Most applications are usually only interested in “persistent” volumes, such as hard disks, floppies, or CD-ROMs, but you can also create BVolumes to virtual file systems, such as /pipe.

Here’s what a BVolume knows:

The volume’s name, device ID, and “root directory.”
Its storage capacity, and the currently available storage.
If the volume is on a media that’s removable.
If the volume’s storage is persistent (as opposed to the ephemeral storage you get with virtual file systems).
If the volume is accessed through the network.
If the file system uses MIME as file types, if it responds to queries, and if it knows about attributes.

Initializing a BVolume¶

There are two ways to initialize a BVolume:

You can initialize it directly using a device ID (dev_t) that you pass to the BVolume constructor or SetTo() function. You can get a device ID from the device field of an entry_ref or node_ref structure. This method is useful if you have a file and you want to know which volume it lives on.
If you want to iterate over all the mounted volumes, you can ask a BVolumeRoster object to get you the “next” volume (BVolumeRoster::GetNextVolume()). You can also ask the BVolumeRoster for the “boot” volume. This is the volume that was used to boot the computer.

Mount and Unmount¶

A BVolume object can’t tell you directly whether the device that it represents is still mounted. If you want to ask, you can call a status_t-returning BVolume function; if the function returns B_BAD_VALUE, the device is no longer mounted.

Furthermore, you can’t ask a BVolume to unmount itself. If you want to be told when devices are mounted and unmounted, you have to ask the Node Monitor to help you. Call watch_node() thus:

watch_node(NULL, B_WATCH_MOUNT, messenger);

messenger is a BMessenger object that acts as the target of subsequent mount and unmount notifications. See “The Node Monitor” section of this chapter for details.