procfs Demo

Description

Demonstrates the /proc filesystem interface for exposing kernel information and accepting commands.

Features

• Directory creation (/proc/demo/)
• Read-only files (info, stats)
• Write-only files (control)
• seq_file interface for complex output
• Runtime control via echo commands

Build & Test

make
sudo insmod procfs_demo.ko

# View information
cat /proc/demo/info
cat /proc/demo/stats

# Send commands
echo "enable" | sudo tee /proc/demo/control
echo "disable" | sudo tee /proc/demo/control
echo "reset" | sudo tee /proc/demo/control

# Watch info change
watch -n 1 cat /proc/demo/info

# Cleanup
sudo rmmod procfs_demo

/proc Entries Created

Path	Mode	Purpose
/proc/demo/	directory	Container
/proc/demo/info	0444 (r–r–r–)	Device information
/proc/demo/stats	0444 (r–r–r–)	Statistics (seq_file)
/proc/demo/control	0200 (-w——-)	Command interface

Commands

• enable - Enable device
• disable - Disable device
• reset - Reset counter

Example Session

$ sudo insmod procfs_demo.ko
$ cat /proc/demo/info
Device Information
==================
Enabled: no
Count: 0
Status: idle
Jiffies: 4294892314

$ echo "enable" | sudo tee /proc/demo/control
$ cat /proc/demo/info
Device Information
==================
Enabled: yes
Count: 1
Status: enabled
Jiffies: 4294893142

$ cat /proc/demo/stats
=== Device Statistics ===
Boot time: 17179569
Operations: 1
Status: enabled
HZ: 250
PAGE_SIZE: 4096

Configuration:
  Enabled: yes

Learning Points

Simple vs seq_file

• Simple read: Small, fixed output (info file)
• seq_file: Multi-line, complex output (stats file)
• seq_file handles pagination automatically

File Permissions

• 0444 (r–r–r–): Read by all
• 0200 (-w——-): Write by root only
• 0644 (rw-r–r–): Read all, write root

Why Use /proc?

• Debugging: Expose internal state
• Monitoring: Runtime statistics
• Configuration: Runtime control
• User-friendly: Standard tools (cat, echo)

Common Uses

• Device status reporting
• Performance statistics
• Debug information
• Runtime configuration
• Kernel module parameters

Modern Alternative: sysfs

For new code, prefer sysfs (/sys) over procfs:

• procfs: Process information, legacy interfaces
• sysfs: Device and driver information

Advanced: seq_file Operations

static const struct seq_operations seq_ops = {
    .start = seq_start,
    .next  = seq_next,
    .stop  = seq_stop,
    .show  = seq_show,
};

Used for iterating over data structures.