Re: [PATCH] Corrections to Documentation/rbtree.txt

Ian Abbott
2008-03-26T14:09:55Z

On 25/03/08 18:24, Rob Landley wrote:
> On Tuesday 25 March 2008 06:02:22 Ian Abbott wrote:
>> On 20/03/08 18:39, Rob Landley wrote:
>>> On Thursday 20 March 2008 10:29:57 Ian Abbott wrote:
>>>> From: Ian Abbott <abbotti@mev.co.uk>
>>>>
>>>> The description of the rb_entry() macro in Documentation/rbtree.txt
>>>> seems incorrect. This patch improves it (hopefully). Also I changed the
>>>> example code to call the previous 'my_search()' example instead of an
>>>> undefined 'mysearch()'.
>>> I have no objection to the patch (and the my_search thing seems like an
>>> obvious typo), but is there a reason to prefer rb_entry() rather than
>>> container_of()? If so, the rationale might be a good thing to add to the
>>> documentation...
>> I don't know the rationale, but all the code I can see uses rb_entry()
>> and not container_of().
>
> Except container_of() works, which is a nice thing to know, and it already
> mentions rb_entry() as another way to do it. If someone could explain _why_
> to use one over the other, that would be a good thing to add.

Let's see if Andrea Arcangeli can still remember the rationale from 9
years ago! :-)

container_of() works just as well, but _none_ of the existing code in
the kernel uses it to access the container of the struct rb_node; they
all use rb_entry(), including the example code in include/linux/rbtree.h.

> Again, I don't care much either way, I just want to know what the point is of
> choosing one over the other that makes changing what's there worth bothering
> with. You're changing the documentation to hide the fact that rb_entry() is
> basically another name for container_of(), and this is supposed to be an
> improvement?

Personally I have no preference for rb_entry() over container_of(), but
as all the code in the kernel uses rb_entry() it seems better if the
examples in the documentation use it too.