The types of resource managers

There are two types of resource managers:

The type you use depends on what you want the resource manager to do, as well as on the amount of work you want to do yourself in order to present a proper POSIX filesystem to the client.

Device resource managers

Device resource managers create only single-file entries in the filesystem, each of which is registered with the process manager. Each name usually represents a single device. These resource managers typically rely on the resource-manager library to do most of the work in presenting a POSIX device to the user.

For example, a serial port driver registers names such as /dev/ser1 and /dev/ser2. When the user does ls -l /dev, the library does the necessary handling to respond to the resulting _IO_STAT messages with the proper information. The person who writes the serial port driver is able to concentrate instead on the details of managing the serial port hardware.

Filesystem resource managers

Filesystem resource managers register a mountpoint with the process manager. A mountpoint is the portion of the path that's registered with the process manager. The remaining parts of the path are managed by the filesystem resource manager. For example, when a filesystem resource manager attaches a mountpoint at /mount, and the path /mount/home/thomasf is examined:

Identifies the mountpoint that's managed by the process manager.
Identifies the remaining part that's to be managed by the filesystem resource manager.

Examples of using filesystem resource managers are: