[OE-core] [for-master][RFC PATCH 0/3] Support template files for wic wks

[Christopher Larson]

On Mon, May 2, 2016 at 7:23 PM, Christopher Larson <kergoth at gmail.com>
wrote:

> From: Christopher Larson <chris_larson at 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.


One downside to this approach is, afaik,  that it's the first serious
deviation between wic outside and wic as an image type. One alternative
would be to parse the template at parse time to inject vars into WICVARS,
but let wic process the template, but then of course a change to the
template without re-running bitabke wouldn't update WICVARS and the written
env files.
-- 
Christopher Larson
kergoth at gmail dot com
Founder - BitBake, OpenEmbedded, OpenZaurus
Maintainer - Tslib
Senior Software Engineer, Mentor Graphics
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