Le 02/05/2016 21:23, Christopher Larson a écrit :
From: Christopher Larson <chris_lar...@mentor.com>
This adds support for .wks.in files as WKS_FILE.
These files are treated as the contents of a bitbake variable, so
usual
bitbake variable references are supported. I considered using another
templating mechanism, for example the one used by yocto-layer, but
then we'd
end up largely mapping metadata variables to template fields anyway,
which is
a pointless indirection. Let bitbake expand the variables directly
instead.
This feature lets us, for example, reference ${APPEND} in --append,
and avoid
hardcoding the serial console tty in the wks file, and let the user's
changes
to APPEND affect wic the way they do the other image construction
mechanisms.
The template is read in and set in a variable at parse time, so
changes to the
variables referenced by the template will result in rebuilding the
image.
It's been suggested that the name should better reflect how its
contents are
used, i.e. .bbin or so. I've also considered including something like
'bbv' or
similar, to indicate its contents are that of a bitbake value. I think
this
should be discussed.
I'd love to hear questions or comments on this. I think the value is
clear,
and it's something we need to solve, but I'd like to hear if others
agree or
disagree on that, and whether this implementation is appropriate.
We have been discussing this a bit with Chris on IRC and i'll add a
couple of thoughts we had so that discussion isn't completely lost.
As a final user of yocto, I find the need for templating in wic very
usefull, it would allow me to specify disk size in the machine
specification and adapt the wic image accordingly, or use different disk
names ( mmcblk vs sda)
however my need is more generic and I think it would be interesting to
consider a bigger problem : using yocto variables in configuration
files. (I mean files in /etc/ here, not yocto configuration)
It is a pretty common problem to have to tailor configuration files for
particular machines, distro features, optional dependencies etc... this
is possible to do using OVERRIDES but it can only be done at the
whole-file level, not within a configuration file. Moreover it makes
some complex cases very tricky. let's present an example
It is pretty common to need to include the build-machine's ip address
in a configuration file. This can be usefull to send logs if the build
machine is also the developer's machine. The ip address of the build
machine can be easily obtained via python and put into the bitbake
environement, but using that variable to set a value in a random file in
/etc is pretty tricky.
similarly, I like to include my public ssh key as an authorized key for
root on my builds, il makes testing way easier
I think having a generic templating mechanism that would recognise some
source files as needing template extension would be awesome. I don't
understand fully how bitbake/yocto works, so I can't design a complete
archtecture, but here are a couple of thought we had with Chris on IRC
* recognise *.in in the same way *.patch are recognized. Is there a
risk of improper expansion ? maybe specify that templating is needed as
a parameter in SRC_URI
* should expansion be in do_fetch or do_patch or somewhere else...
images tend to skip do_patch, but do_fetch is on the bitbake side IIUC.
would that be a problem ?
* interaction with sstate and rebuilding needs to be considered...
changes need to be detected post-templating obviously
Overall, I really like the idea of this patch, there are lot of things
in a .wks that need expansion, but I think there is even more in every
other configuration file of the system.
Hope my random thoughts helped
Regards
Jérémy Rosen
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