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Day 17 - sysfs vs ioctl

Summary

Implemented sysfs attribute (debounce_ms) and compared it with ioctl.

What I Learned

  • sysfs is part of Linux device model
  • sysfs attributes are tied to struct device
  • device_create() 4th argument is critical (drvdata)
  • sysfs and ioctl can share the same backend state

Debug Experience

  • sysfs file existed but cat failed
  • root cause: dev_get_drvdata(dev) returned NULL
  • fixed by passing mydev into device_create()

Key Insight

Control plane can have multiple interfaces:

  • sysfs (text-based)
  • ioctl (binary)

But both must operate on the same internal state.

Design Thinking

  • sysfs is ideal for simple configuration (debounce_ms)
  • ioctl is better for structured control (GET_STATUS, CLR_EVENTS)
  • read/poll is for event data

Reflection

This is the first time I clearly see separation of:

  • data plane (read/poll)
  • control plane (sysfs/ioctl)

The design is much cleaner and more scalable.