[svlug] Source Code Walk-through -- Analysis Tools

Kristian Erik Hermansen kristian.hermansen at gmail.com
Sat Nov 3 20:54:27 PST 2007

My Linux developer friend Peter Petrakis, who works at Stratus on
fault-tolerant OS/driver hardening, gave some advice.  I think the
presenter and attendees may find it useful :-)

You can see his LinkedIn profile below.  He used to work on AlphaLinux
many years ago...

---------- Forwarded message ----------
From: Peter Petrakis <peter.petrakis at gmail.com>
Date: Nov 3, 2007 9:42 PM
Subject: Re: [svlug] Please read and respond - I suggest postponing
1st code walk-thru mtg
To: Kristian Erik Hermansen <kristian.hermansen at gmail.com>

Opengrok is about the best thing I've ever
used,http://www.opensolaris.org/os/project/opengrok/. It's like using
LXR but with syntax highlighting and better search capabilities. He
should consider scripting his presentation using javascript or
something similar. That or re-examine the whole code walk through
think entirely and prepare the code he'll examine in advance.

Problem with these fancy data mining tools is sometimes they mess up
and it takes you a couple clicks to find what you're looking for.
That's OK when you're working in your office but could be awkward and
stressful when you're on stage IMHO. The most rock solid and least
sexy way to browse source code is using cscope. Also, sometimes the
best way to understand a new feature is to look at the diffs. meld is
really good for that.


On 11/3/07, Kristian Erik Hermansen <kristian.hermansen at gmail.com> wrote:
> Any ideas on how to best browse Linux sources in front of an audience
> for this guy who is going to be filmed @ Google doing Linux source
> code walkthroughs?
> Forwarded Conversation
> Subject: [svlug] Please read and respond - I suggest postponing 1st
> code walk-thru mtg
> ------------------------
>  From: Darlene Wallach <freepalestin at dslextreme.com>
> To: SVLUG <svlug at lists.svlug.org>
> Cc: Leslie Hawthorn <lhawthorn at google.com>, Tiffany Griffith
> <tgriffith at google.com>
> Date: Sat, Nov 3, 2007 at 6:30 PM
> All,
> I have a concern that we are not ready to start
> the Linux kernel code walk-through meetings. I
> want to make sure we are putting the very generous
> offer of Google to host us to the best possible use.
> I also want to make sure we are making the best use
> of our time to participate and have our meetings
> filmed.
> I have not seen a syllabus/curriculum for the
> upcoming Linux kernel code walk-through.
> I assert we should have a suggested
> syllabus/curriculum, which specific kernel code
> we will use, a specific editor, etc. so that
> everyone is looking at the same code and seeing
> the same line numbers - this would seem to especially
> benefit people who will view via the video. What
> else should be common for everyone? What am I not
> listing?
> I suggest we have a link on svlug.org which lists
> everything so that people who want to participate
> can look there to see where we are - what we have
> covered, what we plan on covering (in case they
> want to come to a specific meeting).
> Are there people interested in the code walk-through
> that want to propose different aspects? If different
> people take on the tasks it won't all land in the
> hands of one person. I assume most people have day
> jobs, family/relationship responsibilities. So most
> people will not have a lot of extra time on their
> hands.
> Are there people who concur with my assertions and
> suggestions?
> Are there people who offer to take on doing some of
> the work?
>   - which specific kernel should we use
>   etc.
> Here is what I have seen posted in regards to what
> to cover/do:
> Srihari Raghavan
>     Sort of a junior-level Linux experience guy here.  I was wondering,
> if there is currently, and if not, is there any interest...in having
> intensive source code walk-through sessions for Linux kernel.
>      To get an idea of what I am talking about, some thing along the
> lines of:
> http://www.mckusick.com/courses/2006.advdescrip.html
> and in another post Srihari wrote:
> My 2c w.r.t suggestions...
>      a. Filming it for youtube is great, but it could be worthwhile to
> do it after a few sessions, as that would give us time to make the
> sessions more structured, settle down on topics, identify ways of
> conducting these sessions etc.,
>      b. Regarding topics, these are some thoughts...IMHO.  In general,
> it would be good to understand "Design Patterns in Kernel
> software"...how does Linux solve (in terms of in-depth data structures,
> algorithms) the many well known aspects of OS/kernels....some examples:
>          1. How does Linux work with diff. HW...essentially kernel
> startup, machine dependent/independent code, working in a small
> processing/memory footprint device, logical volumes etc.,
>          2. Process creation/handling, system calls, interrupts,
> interrupt handlers, BH handlers, kernel synchronization methods etc.,
>          3. Scheduler - how does it handle interactive vs. CPU intensive
> processes..O(1) scheduler using priority queues/red-black trees, process
> synchronization etc.,
>          4. Memory handling - slab allocator and other types, virtual
> memory, memory alloc/dealloc tracking, handling leaks,
> paging/segmentation etc.,
>          5. Linux kobjects, sysfs, modules, driver interfaces etc.,
>          6. Networking stacks, Filesystem internals, SMP,
> virtualization...and other advanced topics.
>      c. I personally would be fine with pre-meeting prep, but if the
> group decides to go with homework or both, its fine by me.
>      d. Typical kernel source code archives are
>          http://fxr.watson.org/fxr/source/?v=linux-2.6
>          http://lxr.linux.no/
> ====================================
> Andrew Wilcox
> I have an old book that describes the Linux 2.2 kernel, "Linux Core
> Kernel Commentary".  Maybe someone could write an update to 2.6 for
> it.  It would seem like an interesting project (I personally don't
> have the time for it right now, however).  It's a fantastic book -- it
> covers some of the "stranger" parts of the kernel (i.e. SMP,
> scheduling) in more understandable terms than just the source code.
> It also contains a full print out of the whole core of the kernel
> code, cross-referenced with the commentary.
> Here's a link to the book on Amazon:
> http://www.amazon.com/gp/product/1576104699
> Also, there seems to be a 2nd edition for the 2.4 kernel at
> http://www.amazon.com/gp/product/1588801497 -- I do not personally
> have this edition, but it may be worth looking in to.
> and in another post Andrew wrote:
> Not sure if we might want to discuss the multiboot record or not?
> Fairly trivial, but probably worth mentioning.
> (this was in response to Bruce Coston)
> ====================================
> Akkana Peck
> I don't mind pre-session assignments like that. But depending on the
> module we're reading, it might help to have someone give some
> background in what the module does if it's not obvious, so we're
> not just blindly reading lines of code and trying to guess.
> It would be really cool to have homework like "Now try tweaking this
> code to do foo" and see what people come up with and what problems
> they have.
> That would be excellent if people wanted to cover different types of
> modules.  Some might be more interested in scheduler details, some
> in network algorithms, some in USB drivers. But that'll become
> clearer after several sessions -- we're probably fine with one group
> initially.
> and in another post Akkana wrote:
> Several people have expressed interest in startup and init.
> I'm not sure if there's a lot of interesting actual kernel code
> involved there, but if there is, I'd be interested too.
> How the process table is managed might be another good place
> to start (and we'd get a better understanding of things like
> those pesky zombie processes).
> Specific kernel areas I'd love to learn about:
> - ACPI and power management, how suspend (to RAM or disk, but
>    especially RAM) and ACPI sleep states are managed, and what
>    happens on resume. And what's up with those unkillable daemons
>    running in kernel space?
> - Udev.
> - The "completely fair scheduler" and how it can help desktop
>    processes (and it would be interesting to hear ways that the CK
>    scheduler might have differed, if anyone knows).
> - A USB driver or two -- device drivers are one of the areas where
>    it might be most possible to contribute, and so many devices are USB.
>    (Maybe choose some USB class where a lot of devices still don't
>    have drivers, like webcams.)
> - The new wireless infrastructure, and analyze any specific wireless
>    driver -- as with USB drivers, it's an area that needs help, so if
>    we can learn how the system works, we might be able to contribute.
> ====================================
> Larry Colen
> I suspect that just doing
> anything along these lines will have the very significant effect of
> giving other people the idea of holding these code walkthroughs.
> I would like to suggest that at each meeting we ask someone to
> volunteer to note down any potential bugs, or documentation errors.
> Code walkthroughs are helpful for more than just people learning the
> code.
> http://www.linuxjournal.com/article/4388
> and in another post Larry wrote:
> I find that having context really helps me learn things like this, so
> I think that a good place to start would be a high level overview. The
> general structure of the kernel.
> Online supplements would be URLs of good places to look for info, and
> maybe some faqs for etiquette on the lkml etc.
> For digging into the code, I'd probably want to start with a fairly
> high level look at what happens when init() is called.
> ====================================
> bruce coston
> Beginning should be easy, Boot - probably with GRUB as its the most
> common method now. Or start just after that as GRUB is not the kernel
> itself.
> ====================================
> Philip Martin
> I think there's some interesting stuff there.  All the PCI bus
> initialization, which would provide a nice segue into device driver
> loading and ACPI.  The whole init process (as in /sbin/init) is
> outside the kernel, but would be a great place to start looking at the
> linux process lifecycle, process table and scheduler.
> Maybe we should group things into umbrella concepts which can be
> covered in a number of sessions.  Each session should be as atomic as
> possible, however, to enhance retention.  Something like:
> major kernel data structures (atomic_t, kernel_size_t, etc),
> conventions (locking), utility functions, etc.
> booting and device discovery (ACPI, bus initialization, device
> discovery, device driver loading, udev)
> process management (process lifecycle, process table, process scheduler,
> etc)
> device drivers (general framework, specific types, etc)
> VFS (VFS layer, IO scheduler, ext2, ext3, etc)
> VM
> etc.
> The progression should be logical and should hopefully build upon what
> has come before.
> ====================================
> Brian J. Tarricone
> is there a need to standardise on a
> particular version that everyone will follow?  Presumably 2.6 will be
> covered, but, for example, 2.6.12 is very different from 2.6.23, since
> active development is occurring on the 2.6 series.  Things like the
> recent addition of a new CPU task scheduler, a new default memory
> allocator, and even many of the VM changes occurring early in the 2.6
> series might make for some confusion if people are on different versions.
> _______________________________________________
> svlug mailing list
> svlug at lists.svlug.org
> http://lists.svlug.org/lists/listinfo/svlug
> --------
>  From: Tejas Kokje <tejas.kokje at gmail.com>
> To: svlug at lists.svlug.org
> Date: Sat, Nov 3, 2007 at 7:13 PM
> [Quoted text hidden]Darlene,
> For curriculum, how about following chapter order of one of the published
> kernel books like "Understanding the Linux Kernel" ?  We need not to follow
> it strictly, but it can always act as a guideline.
> As for kernel version, how about 2.6.23 since it has new CFS scheduler ? We
> all will be on same page if we get same kernel. Something from kernel.org.
> Like
> ftp://ftp.kernel.org/pub/linux/kernel/v2.6/linux-2.6.23.tar.gz
> If I understand correctly, this tarball is not going to change even when
> future versions of kernels are released.
> For editor, I don't think it matters. Good old vi with ctags will do it (yeah,
> emacs users ..flame me). Everybody is free to use whatever they like.
> I strongly feel that we should meet on Tuesday. If not for kernel
> walkthroughs, atleast to discuss about the issues you raised. We can divide
> responsibilites when we all meet. First meeting can remind us of first day of
> course at school (only discuss logistics, course overview etc with dates for
> midterms & finals :-D)
> I think discussing these issues asynchronously through mailing list might not
> be the best way and end up taking more time.
> Everybody else, chime in.
> Tejas Kokje
> [Quoted text hidden]
> --------
>  From: Akkana Peck <akkana at shallowsky.com>
> Reply-To: svlug at lists.svlug.org
> To: svlug at lists.svlug.org
> Date: Sat, Nov 3, 2007 at 7:36 PM
> Darlene Wallach writes:
> > I have a concern that we are not ready to start
> > the Linux kernel code walk-through meetings.
> [ ... ]
> > I have not seen a syllabus/curriculum for the
> > upcoming Linux kernel code walk-through.
> I'm not too worried. I'm very much aware this is a volunteer thing
> thrown together very quickly -- I'm guessing Paul is still trying
> to decide what's best to do first, and how fast we'll be able to
> follow.  It might take a few meetings to figure that out.
> I'm all for jumping right in and learning some basics while
> we all figure out how these sessions should be run.
> Once things are rolling and there's a plan several weeks in
> advance, I love your idea of having all the info on svlug.org
> so people will know where we are and what to prepare for next.
> I'm certainly willing to help with that.
> > which specific kernel code we will use,
> I do agree that we should decide on a specific kernel version
> beforehand, so we don't have to spend the whole first session
> fighting with wi-fi configuration, waiting for downloads,
> configuring and building.
> Paul, is (the latest stable version) a reasonable choice
> for us to have ready on our laptops?
> > a specific editor, etc.
> Oh, now you're talking about restricting our choice of religion! :-)
> Seriously, I expect most people will use whatever editor is
> most familiar to them on the privacy of their own laptops.
> However, for future documentation on svlug.org, it might be
> good to pick a favorite web source viewer, e.g. LXR.  I found
> http://fxr.watson.org/fxr/source/?v=linux-2.6 for the git version, but
> nothing that has 2.6.23. Are there any better search/display tools?
> --
>     ...Akkana
>     "Beginning GIMP: From Novice to Professional": http://gimpbook.com
> [Quoted text hidden]
> --------


Kristian Erik Hermansen

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