On Sat, Dec 17, 2011 at 1:58 AM, Jeff Haran <jharan@xxxxxxxxxxxxxx> wrote: >> -----Original Message----- >> From: kernelnewbies-bounces@xxxxxxxxxxxxxxxxx [mailto:kernelnewbies- >> bounces@xxxxxxxxxxxxxxxxx] On Behalf Of Alexandre Courbot >> Sent: Monday, October 24, 2011 7:05 PM >> To: Jimmy Pan >> Cc: Kernelnewbies@xxxxxxxxxxxxxxxxx >> Subject: Re: Is there a way to build a cross reference with kernel > file >> >> On Tue, Oct 25, 2011 at 12:00 AM, Jimmy Pan <dspjm1@xxxxxxxxx> wrote: >> > It seems we can use ctags, while, I don't really know how to > implement it. >> > 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 Martínez Canillas (+34) 682 39 81 69 Barcelona, Spain _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
