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Patrick Mochel

Patrick Mochel gets paid to play with big toys and have a lot of fun, while occasionally moonlighting as a kernel hacker. Patrick has made numerous contributions to the Linux kernel.

Patrick is giving a talk on Linux's SysFS

Sysfs - A Unified, Safe, and Extensible Model for Exporting Kernel Attributes

All subsystems in the kernel currently have some way of exposing and/or modifying attributes during runtime. Typically, this is done via procfs or sysctl.

While these mechanisms are relatively easy to use, they expose several problems. The implementation of both is old and often neglected. There are no formatting or content standards for procfs. The processing and formatting of data is the responsibility of the owner of the file. These implementations are usually copied from other implementors, and usually buggy.

Driverfs was created to expose the the kernel data structures of the new driver model, including physical devices, as well as bus, class, and device-specific drivers, and the linkage between each. Each entity gets a directory in the filesystem, creating a standard, default location to expose attributes to userspace.

Driverfs provides an interface to very easily define type-safe attributes. The owners of the attributes are free from the responsibility of formatting and parsing the data, preventing several bugs alone. Plus, all events are properly synchronized and objects reference counted, preventing against race conditions.

Driverfs is also extensible. It allows any group of objects to maintain a hierarchy and expose an interface to export type-safe and race-free attributes.

During the 2002 Kernel Summit, it was decided that other subsystems should have such an easy and safe interface to export attributes. Instead of creating separate filesystems for each subsystem to expose attributes, Linus said to use the same filesystem.

This decision is causing driverfs to be renamed to sysfs. The interfaces and structures are being refined. Other subsystems are being converted to use it instead of their own procfs or sysctl format.

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