1 / 12

Linux Device Drivers overview

Jeff Foster. Linux Device Drivers overview. Introduction. Goals of Linux Device Drivers Teach people how to write drivers Teach people some programming tricks Serve as reference Target audience: Linux user with no kernel knowledge ...but with a deep understanding of their device.

aleda
Download Presentation

Linux Device Drivers overview

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Jeff Foster Linux Device Driversoverview

  2. Introduction • Goals of Linux Device Drivers • Teach people how to write drivers • Teach people some programming tricks • Serve as reference • Target audience: • Linux user with no kernel knowledge • ...but with a deep understanding of their device Linux Device Drivers overview, September 12, 2000

  3. (Some of) Our Goals • Find bugs in existing drivers • Show existing drivers don’t have bugs • Help people write new drivers • Mismatch with book Linux Device Drivers overview, September 12, 2000

  4. What to Look For • Discussion of common mistakes • API requirements (KPI?) • driver functions return positive ints on success, negative ints on failure (pp50-51) • kernel won’t call non-blocking I/O functions if previous request still pending (p264) • Invariants • “every kernel function that calls kmalloc (GFP_KERNEL) should be reentrant” (p153) Linux Device Drivers overview, September 12, 2000

  5. What to Ignore • Warning: Out of date! • Written for 2.0.x, little bit on 2.1.x (Chap. 17) • 2.4.x will be released soon • Locking got a lot finer • Symbol table interface changed • Many fast/slow call distinctions gone • /dev changing in the future (currently awful) Linux Device Drivers overview, September 12, 2000

  6. Other Places to Look • The source code! • linux/include/blk.h: “All functions called within end_request() must be atomic.” • Patches to the source (2.2.14) linux/drivers/char/acquirewdt.c -unregister_reboot_notifier(&acq_notifier); +register_reboot_notifier(&acq_notifier); • Linux kernel mailing list (high volume) • The web Linux Device Drivers overview, September 12, 2000

  7. Partial Directory Layout • /usr/src/linux /arch architecture-specific stuff /i386 sometimes you have to look here /drivers device drivers /char character devices -- most modular /block block devices -- more integrated ... /init boot up code /kernel the core OS (e.g., scheduler) /mem black magic • Also /fs, /net, /lib, ... Linux Device Drivers overview, September 12, 2000

  8. Kernel Architecture • It looks like only /drivers interesting • ...but the kernel is more monolithic than it looks • ...especially block devices (buffer management) • char devices better behaved • Start here Linux Device Drivers overview, September 12, 2000

  9. Topic 1: Locking • Four kinds of locks in kernel • Spin locks and read-write locks • Interrupt enable/disable • Sometimes combined, e.g., spin_lock_irq • Whole kernel lock • Locks are used all over the place • Are they used correctly? consistently? Linux Device Drivers overview, September 12, 2000

  10. Topic 2: Interrupt Time • When in_interrupt is true, code cannot • Access current • Call the scheduler (may sleep) • Call kmalloc(GFP_KERNEL) (may sleep) • Copy to/from user-space (may sleep) • more? • Also see Dawson Engler’s work Linux Device Drivers overview, September 12, 2000

  11. Topic 3: Resource Allocation • Drivers get and release system resources • Memory • IRQs • module numbers (maybe) • space for their code (mod usage count) • Are the resources handled correctly? • Leaks lead to instability -- reboot to reclaim Linux Device Drivers overview, September 12, 2000

  12. What We’re Missing • Many errors in drivers are with device interface, not kernel interface • see patch files • No device-specific info in book • How do we find these bugs? Linux Device Drivers overview, September 12, 2000

More Related