[OE-core] how to see the *effect* of changing the configuration for a build?

[Robert P. J. Day]

  ok, i'm just going to ask for piles of advice on what (bitbake)
commands and options i can use to see the effect of various changes to
a build's configuration as part of a tutorial.

  as a starting point, i've built a core-image-minimal target for a
qemuarm machine, just to keep things simple so this doesn't require
any hardware.

  i realize i can use variations of "bitbake -e" to see the
environment, but i'm curious if there are shorter ways.  for instance,
if i want to demonstrate how to add a single package to a build, i can
add the following to local.conf:

  IMAGE_INSTALL_append = " strace"

but what's the easiest way to verify that that package will be
incorporated into a new build without actually doing the build?  one
option is to simply do a dry run of fetchall, to see what would need
to be fetched:

$ bitbake -n -c fetchall core-image-minimal
... snip ...
NOTE: Running task 279 of 286 (ID: 21, /home/rpjday/oe/oe-core/meta/recipes-devtools/strace/strace_4.7.bb, do_fetch)
NOTE: Running task 286 of 286 (ID: 1, /home/rpjday/oe/oe-core/meta/recipes-core/images/core-image-minimal.bb, do_fetchall)
NOTE: Tasks Summary: Attempted 286 tasks of which 284 didn't need to be rerun and all succeeded.
$

but that's a bit messy (and if, for some reason, strace has already
been fetched, it wouldn't be listed).  i could also check the bitbake
environment, which i can see has numerous references to "strace".
but is there a cleaner way?  i'd then work my way up to adding more
packages, then IMAGE_FEATURES and so on, showing the effect at each
step, ideally without having to spend time doing a rebuild every time.

  with layers, it's easier as i can use bitbake-layers, so i'm good
with that.  anyway, suggestions as to how to display configuration
changes appreciated.

rday

-- 

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

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
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