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Configfs - Joel Becker


Joel Becker has been breaking computers since his father took him to work as a child. He's been breaking Linux for over thirteen lucky years. He still owns the first machine he ever ran Linux on, and it might even boot.

For the past eight years, he has been breaking - and fixing! - Linux for Oracle. During that time, he has done various and sundry things, some of them reputable. He is the maintainer for configfs and the co-maintainer for ocfs2.


There are multiple ways a driver or subsystem may expose its configuration to userspace. The goal is the same - an entity in kernelspace wants to present an observation and/or configuration interface to userspace. Creating a easy to use interface is a challenge. The methods Linux employs often fit one need well but are ill-matched for another.

configfs solves one particular problem: kernel entities that are created by requests from userspace. An action from userspace causes the entity to be created, presenting the attributes by which it can be configured. An action from userspace is required to remove the entity. Client drivers and subsystems respond to these actions.

configfs is intended to coexist alongside sysfs and procfs. A device discovered by a kernel driver might present its configuration via sysfs; the entity was created by a kernel action. Conversely, the creation of a netconsole target is an action by the user. She asks the kernel to create the new target and then configures it via attributes.

This presentation will discuss the work required to use configfs in a driver or subsystem, as well as the view seen by userspace attempting to configure that subsystem. The netconsole driver's simple use case will be used to explain the basic concepts. Emphasis will be made on the separation between the entities and the filesystem view; a subsystem should not need to know it is part of a pseudo-filesystem.

The presenter is the author and maintainer of configfs. It was originally written to configure the ocfs2 cluster stack.