The major focus for many Linux developers has been in those parts of the kernel that support server type applications. However a rapidly expanding area of Linux development has been in the desktop applications area. A key aspect of this has been in the use of USB peripherals - especially keyboards, mice and mass storage devices. The hot-plug nature of USB devices has caused some of the underlying assumptions about Unix type devices to be re-assessed, and new or modified approaches to be adopted.

Linux USB development started in 1997, and has had a somewhat tortured history, with splintered development and several re-writes. It captures many of the issues associated with open source development - difficulty in obtaining device programming information, differences in opinion between developers concerning architecture, devices that are "almost but not quite" compliant to published specifications, and the difficulty in finding enough time to get all that coding, testing and documentation done.

The introduction of USB 2.0, with significantly higher speeds, has required some new drivers, but has also identified speed and efficiency problems with some of the existing drivers. Future enhancements to include new drivers, and improve existing ones, seem likely. As Linux emerges to become an important part of the desktop market, more manufacturer support is expected.

This talk will provide a brief overview of how Linux USB support got to where it is today, what the current capabilities of Linux USB are, and likely directions for future support. The talk will also cover how key elements of Linux USB work, with some digression into the Linux Input layer subsystem, since most users experience USB through USB keyboards, mice and joysticks, which are jointly supported by USB and Input subsystems. Likely changes to the way in which user space applications (such as the X Windowing System and games) are managed will also be overviewed.

The talk will also cover how Linux Hotplug works, and how it can be used to implement "policy" decisions for individual systems, without needing to implement changes to the kernel.

Brad Hards is the technical director of Sigma Bravo Pty Limited, a small engineering services company based in Canberra, Australia.

He has been a Linux user since 1993, when he download Slackware, one floppy disk at a time, over a modem link.

Brad Hards is a current kernel maintainer (USB CDC Ethernet class driver) and has written documentation for several open source activities, including the Linux USB guide. He ran a BoF at linux.conf.au 2001, and presented a paper on Linux USB at linux.conf.au 2002.