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From: Richard Purdie <richard.purdie@linuxfoundation.org>
To: petter@technux.se
Date: Sun, 11 May 2014 13:13:00 +0100
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Cc: Patches and discussions about the oe-core layer
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Subject: Re: [PATCHv2 01/13] systemtap: remove usage of FILESPATH
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On Sun, 2014-05-11 at 00:31 +0200, petter@technux.se wrote:
> 2014-05-10 18:58 skrev Khem Raj:
> 
> > On Sat, May 10, 2014 at 1:05 AM, Petter Mabäcker <petter@technux.se>
> > wrote:
> >
> >> +FILESEXTRAPATHS_prepend := "${THISDIR}/systemtap:"
> >
> > would something like
> >
> > FILESEXTRAPATHS =. "${FILE_DIRNAME}/systemtap:"
> >
> > avoid the prepend and immediate evaluation
> 
> I guess someone with deep bitbake knowledge can answer this better. But 
> as far as I understand, you should always use immediate evaluation when 
> using THISDIR, to be extra safe. Not sure if it's more safe to use 
> FILE_DIRNAME if you want to avoid immediate expanding when using 
> FILESEXTRAPATHS?
> 
> The bitbake documentations says:
> 
> "The operators "_append" and "_prepend" differ from the operators ".=" 
> and "=." in that they are deferred until after parsing completes rather 
> than being immediately applied."
> 
> Not sure if above means that "=." will also immediately expand 
> variables or not?

They're not.

> Personally I have always used FILESEXTRAPATHS_prepend := 
> "${THISDIR}/<somename>:" like the yocto documentation recommends. But 
> sure if you can avoid immediate expanding in FILESEXTRPATHS, that would 
> mean a tiny optimization. In that case perhaps the documentation should 
> be updated as well. Looking in meta-layer both methods seems to be used.

What Khem means is that in the case we know we're in the .bb file
directory, we can use FILE_DIRNAME instead of using :=.

Why? FILE_DIRNAME is defined as:

conf/bitbake.conf:FILE_DIRNAME = "${@os.path.dirname(d.getVar('FILE'))}"

FILE will point to the .bb file.

Cheers,

Richard