Messages in this thread | | | Date | Sun, 17 Dec 2017 23:33:01 +0100 | From | Luc Van Oostenryck <> | Subject | Re: [RFC patch] checkpatch: Add a test for long function definitions (>200 lines) |
| |
On Sun, Dec 17, 2017 at 01:46:45PM -0800, Linus Torvalds wrote: > On Sat, Dec 16, 2017 at 5:26 PM, Joe Perches <joe@perches.com> wrote: > >> > >> I'm not expecting you to be able to write a perl script that checks > >> the first line, but we have way too many 200-plus line functions in > >> the kernel. I'd like a warning on anything over 200 lines (a factor > >> of 4 over Linus's stated goal). > > > > In response to Matthew's request: > > > > This is a possible checkpatch warning for long > > function definitions. > > So I'm not sure a line count makes sense. > > Sometimes long functions can be sensible, if they are basically just > one big case-statement or similar. > > Looking at one of your examples: futex_requeue() is indeed a long > function, but that's mainly because it has a lot of comments about > exactly what is going on, and while it only has one (fairly small) > case statement, the rest of it is very similar (ie "in this case, do > XYZ"). > > Another case I looked at - try_to_unmap_one() - had very similar > behavior. It's long, but it's not long for the wrong reasons. > > And yes, "copy_process()" is disgusting, and probably _could_ be split > up a bit, but at the same time the bulk of the lines there really is > just the "initialize all the parts of the "struct task_struct". > > And other times, I suspect even a 50-line function is way too dense, > just because it's doing crazy things. > > So I have a really hard time with some arbitrary line limit. At eh > very least, I think it should ignore comments and whitespace lines. > > And yes, some real "complexity analysis" might give a much more sane > limit, but I don't even know what that would be or how it would work. >
It would be very easy to let sparse calculate the cyclomatic complexity of each function (and then either printing it or warn if too high), but: - warning would also need a hard limit - cyclomatic complexity of a function with a big (but simple) switch will also be high.
I far from sure that the cyclomatic complexity is very useful but maybe some variation of it (like counting a switch as a single edge) could have some value here.
-- Luc Van Oostenryck
| |