Device publishers are hardware-support components that publish information on attached devices through the Persistent Publish/Subscribe (PPS) service. Applications use this information to access the content on devices so they can display media information in browsers or invoke multimedia services to read metadata from those devices.
Applications could send commands to device drivers to read device information but this design requires developers to learn hardware interfaces, which is inconvenient. Device publishers offer a reliable source of device information by allowing applications to subscribe to PPS objects to receive device updates. Refer to the Persistent Publish/Subscribe Developer's Guide for details on implementing a subscriber.
The information published for a device includes:
Device publishers are designed for specific hardware types. We ship the following device publishers:
Device publishers don't monitor the physical connection of devices. Other system services monitor hardware events and respond when users attach or detach storage devices (e.g., USB sticks) or when they insert or remove mediastores (e.g., SD cards) from physical slots. For instance, the io-usb server monitors the hardware and reacts to each USB device attachment or detachment by notifying usblauncher.
The publishers run as persistent background processes. Typically, they're launched during bootup. You can restart publishers if they unexpectedly terminate.