[OE-core] questions about WORKDIR and S usage and files/ stuff

[Robert P. J. Day]

On Sun, 22 Feb 2015, Richard Purdie wrote:

> http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=4eb3db9a2ca8eaff64b64b8f56dac25d4734571c
>
> http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=cf72ede74d35746a10d0708942287548f9c72f30
>
> and some of the surrounding patches. I'd assumed base-files was part
> of that series, clearly it wasn't but there were many other recipes
> changed at that time.

  ah, gotcha. so let me just summarize my understanding of this, it
looks pretty straightforward.

  once upon a time, base.bbclass politely(?) auto-created the S
directory for each recipe. this had the potential for screwing things
up if the recipe author didn't set S properly for that recipe.

  solution: stop auto-creating S, leaving the responsibility for
creating whatever S refers to to the recipe itself, typically as a
result of just doing a regular unpack of the SRC_URI. this allows a
trivial sanity check -- whatever directory S refers to should exist as
the result of the simple unpacking of that recipe.

  now, given the default setting in bitbake.conf of

  S = WORKDIR/BP

as long as that value is appropriate for a recipe, then the recipe
author need not set it explicitly. *but*, even in the case where a
recipe doesn't require any "unpacking" -- as in, recipes like
base-files which refer exclusively to local files -- it is still
necessary to set S to *something* that will exist, just to pass that
sanity test, and the easiest solution is to just set it to WORKDIR,
which is guaranteed to exist for *any* recipe.

  final thought on this -- to pass the sanity check, it is necessary
only for the directory referred to by S to exist. the obvious thing to
set it to is, of course, WORKDIR, but in the case of recipes like
base-files which don't even *use* S, it's technically possible to set
it to *any* directory guaranteed to exist. i'm not suggesting this is
a smart thing to do, only that it would be technically viable.

  and all this suggests that, even if you set S = WORKDIR, for
cleanliness, you should still avoid referring to unpacked objects
relative to S, just in case -- it's safer to restrict yourself to
referring to things relative to WORKDIR. is that about right?

rday

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
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