Linux Device Driver Development

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Linux Device Driver Development

• Chris Lydick
• Spring 2007

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Class Schedule
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Textbook List

• J. Corbet, A Rubini, G Kroah-Hartman. Linux
  Device Drivers, 3rd Ed.
• Available for download online!
• http//lwn.net/Kernel/LDD3/

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Operating Systems 101

• Ive not had Operating Systemsbut
• Role of Device Drivers
• Mechanism vs. Policy
• Black Box
• Semi/undefined interface (device) -gt Well defined
  interface (Linux API)

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Operating Systems 102

• Uses C Language
• Gets complicated very quickly (lots of macros,
  code)
• Need to have a sense of ...
• concurrency, race conditions
• interrupts, deferred work
• mutual exclusion
• kernel and user-space memories
• pointers, structures, (lots to consider)

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Operating Systems 103

• Textbook has provided lots of skeletons and
  demos (Wheew!)
• My testbed Fedora Core 4, 2.6.11 (book requested
  2.6.10)
• Should we start with. Hello World?

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Operating Systems 104

• OK, easy So what.
• Before digging deeper, consider 3 types of device
  drivers
• Character Devices (stream of bytes)
• Block Devices (file systems)
• Network Interfaces (duh.)

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Operating Systems 105

• Char devices
• Scull (Simple Character Utility for Loading
  Localities) testbed for Char devices.
• Scull0..3 global/persistent memory
• Scullpipe0..3 FIFO pipes demonstrate contention
• Scullpriv private data for each console

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Operating Systems Lab Exercises

• Scull0 demonstration
• Scullpipe0 demonstration
• Scullpriv demonstration
• Short (Temperature Sensor)
• Shortprint demonstration

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Operating Systems Final

• Other Areas of Interest
• Snull (network interface skeleton)
• USB-Skeleton (yep.)
• PCI-Skeleton (ok.)
• Sample Disk Driver (cool.)
• TTY Drivers, DMA and Memory Mapping, etc.

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Motivation

• My Thesis Supercomputing Cluster in 031
  Rathbone
• USB Connectivity driver timeouts/overflows in
  OpenBSD
• Communicated with Chris Pascoe (OpenBSD Developer)

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Motivation

• Acer Labs M5632 Bridge Cable
• Worked fine using the standard USB 1.0 Driver
• Issues arose with the USB 2.0 (EHCI) driver diff
  file
• Abused the kernel profiling framework to check
  at runtime for kernel stack overflows.
• Were switching to Linux (no issues), but its
  good to know how to dig into drivers right?
• Plus, isnt Linux supposed to be better than
  Windoze?

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Reverse Engineering 101

• Reverse Engineering Getting something to work by
  watching it work when correctly loaded.
• Usually occurs within Windows (sorry, we just
  cant get away from Microsoft!)

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Reverse Engineering 102

• USB Devices (URB)
• USB Analyzer/Sniffer (Snoopy, USB Monitor,..)
• Acts similarly to Ethereal
• /sys/devices/pci000000/0000002.0/usb2/
• PCI Bus
• Hardware Sniffers (much more difficult to
  analyze!)

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Conclusions

• GET THE BOOK! Its very helpful and is a great
  reference!
• Examples are available for download
• Book is freely available (wget it before its
  gone!)
• Next step USB!