On Sat, Dec 17, 2011 at 1:58 AM, Jeff Haran [off-list ref] wrote:

quoted

-----Original Message-----
From: kernelnewbies-bounces at kernelnewbies.org [mailto:kernelnewbies-
bounces at kernelnewbies.org] On Behalf Of Alexandre Courbot
Sent: Monday, October 24, 2011 7:05 PM
To: Jimmy Pan
Cc: Kernelnewbies at kernelnewbies.org
Subject: Re: Is there a way to build a cross reference with kernel

file

quoted

On Tue, Oct 25, 2011 at 12:00 AM, Jimmy Pan [off-list ref] wrote:

quoted

It seems we can use ctags, while, I don't really know how to

implement it.

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I don't want to use the online cross reference every time...

I personally use KDevelop to navigate the kernel. It's not perfect yet
and a little bit tricky to configure correctly, but it's still pretty
efficient and I work on improving it. I wrote about it recently:
http://www.gnurou.org/code/kdevelop-kernel

CTags is also known to work well, actually there is even a 'make tags'
target in the kernel's Makefile.

Hope this helps,
Alex.

I have found that one of the hardest things to deal with when trying to
understand kernel code (or the code for any big project written in C) is
trying to find out where a given structure field is used. For instance,
say you want to find out where the cb field of a sk_buff structure is
referenced. If I use cscope on my kernel source tree and enter "cb"
under "Find this C symbol:", it provides 2596 references. The vast
majority of those references will have nothing to do with sk_buff
structures because cb is used as a variable or field name all over the
place, usually to mean some sort of pointer to a callback function, but
I'd have to sift through all 2596 of them to find the references to the
"right" cb.

I tried kdevelop to solve this same problem. It doesn't seem to provide
any references to structure field names. Hover the mouse cursor over a
field name in kdevelop and nothing pops up like it would for say a local
or global variable name. At least it didn't when I tried it.

Has anybody found a tool the solves this kind of problem well?
Specifically, given a struct foo containing a field named bar, show me
all of the code that references the bar field of struct foos but not the
bar fields of other structures nor instances of variables that are
themselves named bar.

I realize that with things like arbitrary type casting and the C
pre-processor, doing this kind of thing with 100% accuracy could be
quite difficult. But even if it was only partially successful at
eliminating the false positives that come with tools like cscope, it
could save a lot of time.

Well you can always rely on conventions. For the sk_buff example,
generally the kernel uses sk_buff pointers and the variable name is
almost always skb. So git grep skb->cb is a good approach to this.

Also, I think that the first thing one have to learn in the kernel is
the project layout. Where everything is placed and why. I recommend
that the first thing someone getting into kernel dev is getting
familiar with each sub-dir.

One should be able to ask questions such as: Where are the input
drivers? Where is the code for a given filesystem or the support for
an architecture?

So, in your example I would do something like this:

$ git grep "skb->cb" net/

If I want to know the usage of that field in the network core or

$ git grep "skb->cb" drivers/net/

If I want to know how drivers used it.

Again, ETAGS and tools like that are good for pointing where a symbol
is defined, but its usage is a little more trickier. Like you said the
kernel uses _lots_ of functions pointers so I don't think that a tool
that shows me every place a given function is called will be easier
(if possible) to implement.

Hope it helps,

-- 
Javier Mart?nez Canillas
(+34) 682 39 81 69
Barcelona, Spain