[yocto] Where does the bitbake get the variable "TOPDIR"

[Biao]

At 2012-12-19 00:35:13,"Eren Türkay" <eren at hambedded.org> wrote:
>On Tue, Dec 18, 2012 at 08:28:32PM +0800, Biao wrote:
>> >http://hambedded.org/blog/2012/11/24/from-bitbake-hello-world-to-an-image/
>> I will try to give some feedback after finishing the reading.
>> But for now, there are some silly questions:
>> 1. There is a base_do_fetch() {}, I did not find the explanation of the keyword of 'base' in the manual, do i miss something?
>
>I don't know the internals of bitbake on that level but as far as I
>understand, bitbake uses the name of the bbclass file as a prefix in the
>function names for the sake of abstraction. So, as in autotools.bbclass,
>the tasks defined in base.bbclass gets prefixes with "base_" keyword.
>Probably, it's related with mapping the function names when 'inherit'
>keyword is used.
I agree it seems a prefix is mandatory when working with EXPORT_FUNCTIONS.
>
>I'm not clear on this topic either. A hand from an experienced bitbake
>guru would be really helpful here. The type of abstraction in bitbake
>should be explained in detail as well as how EXPORT_FUNCTION works.
>
>Any volunteers?
>
>> 2. There is 'bb.note' and 'bbnote' in the code example, is it a type-mistake or something else?
>
>No, this is not a mistake. You can use python as well as shell functions
>in bitbake recipes and classes. See 'python' keyword in function
>definitons where bb.note is used. That's why python function "bb.note()"
>is used to print log information. Without python keyword, the bitbake
>function is treated as shell.
>
Ok, so the bb.note is a python provided functions, which is missing from the docs.
>Regards,
>Eren
>
>-- 
>    . 73! DE TA1AET
>      http://linkedin.com/in/erenturkay
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