The following is a brief introduction and overview to Nicholas McGuire's technical paper on using the Linux proc filesystem in embedded systems. A link from which you can download the complete 18-page paper (PDF file) is available at the bottom . . .

Introduction and overview

The proc file system is a well established and widely used interface in the Linux kernel. Since the late 0.99.X releases of the Linux kernel, the proc file system has been included in the official kernel releases and has been used in many Linux systems. Its virtual file system interface allows both the inspection of kernel internal data structures and the manipulation of these data structures without requiring additional non-volatile memory.

Although the initial uses of proc focused primarily on network issues, additional applications quickly began using proc files in order to simplify administrative and debug tasks. In the early releases, the proc API was fairly complex; but as of Linux kernel 2.4.X, the interface has become much more user-friendly.

The main features of the proc file system are . . .

• Simple API
  
• Direct access to kernel internals
  
• Simple access via file system-abstraction
  
• POSIX compliant open/ read/ write/ close interface
  
• Kernel level security setting on a file-scope

Although the proc Interface is generally used in desktop and server systems, the focus of this article is on using the proc file system interface in Linux-based embedded and real-time systems, controlling of real-time tasks via proc interfaces, and other ways these systems can benefit from implementing dedicated, appliance-specific, proc interfaces.

In embedded systems with tight resource constraints, small file system footprint is a key issue, as is the requirement for run-time optimization. In such systems, proc file system and related sysctl functions can be used to provide kernel related administrative information via proc, as well as resource-optimized control interfaces, can substantially improve embedded system performance. A further, often ignored, aspect is that the proc and sysctl interfaces allow very precise tuning of access permissions, both increasing the security of the embedded system's administrative interfaces and improving diagnostic precision, which is essential for efficient error detection and analysis.

Key features of the proc interface that are particularly useful for embedded systems are . . .

• Performance — low processing overhead to gain access to kernel internal data structures via proc
  
• Highly configurable interface — enabling a “human readable” window into kernel internals
  
• Runtime monitoring — precise monitoring of system status and resources
  
• Security — well tunable access control based on per-file file-operations and kernel capabilities

This work is part of an on-going GPL project for Keymile AG (Vienna, Austria), where the proc interface is being applied to a series of embedded Linux based high-bandwidth Internet access devices. An associated GPL project which has the objective of developing a proc-based embedded utility set is available here. The project is also available via cvs, cvs -d :pserver:anoncvsopentech.at:/home/gpl login (password: anoncvs), cvs -d :pserver:anoncvsopentech.at:/home/gpl co proc_utils. Feedback to the author is always appreciated.

Read the complete article here . . .

 
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