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Linux Device Driver Development

Chris Lydick

Spring 2007

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Class ScheduleCIS e ( *i) TU 10:30 Intro to Device Drivers Lydick

PSYCH012

MWF 11:30 My Motivation Lydick

EECE92181

MWF 9:30 Reverse Engineering Lydick

LAB0

F 2:30p Demonstrations Lydick

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Textbook ListJ. 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

I¶ve not had O perating Systems«but« ± Role of Device Drivers

Mechanism vs. PolicyBlack BoxSemi/undefined interface (device) -> Welldefined interface (Linux API)

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Operating Systems 102

Uses C LanguageGets 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 ³skeletons´ and demos (Wheew!)My testbed: Fedora Core 4, 2.6.11 (bookrequested 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 typesof 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 : FIF O pipes demonstrate

contention ± Scullpriv : private data for each console

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O perating Systems LabExercises

Scull0 demonstrationScullpipe0 demonstrationScullpriv demonstrationShort (Temperature Sensor)Shortprint demonstration

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13

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Operating Systems« Final

O ther 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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MotivationMy Thesis: Supercomputing Cluster in 031Rathbone:

± USB Connectivity: driver timeouts/overflows inO penBSD

± Communicated with Chris Pascoe ( O penBSDDeveloper)

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MotivationAcer Labs M5632 Bridge Cable ± Worked fine using the standard USB 1.0

Driver ± Issues arose with the USB 2.0 (EHCI)

driver [diff file]³Abused´ the kernel profiling framework to

check at runtime for kernel stack overflows. ± We¶re switching to Linux (no issues), but it¶s good

to know how to dig into drivers« right? ± Plus, isn¶t Linux supposed to be better than

Windoze?

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Reverse Engineering 101

Reverse Engineering: Getting somethingto work by watching it work whencorrectly loaded. ± Usually occurs within Windows (sorry, we

just can¶t 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/pci0000:00/000:00:02.0/usb2/

PCI Bus

Hardware Sniffers« (much more difficult toanalyze!)

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Conclusions

GET THE B OOK ! It¶s very helpful and isa great reference!Examples are available for downloadBook is freely available (wget it beforeit¶s gone!)Next step: USB!