[OE-core] Consistency and use cases for IMAGE_FSTYPES

[Denys Dmytriyenko]

On Thu, Mar 22, 2012 at 11:26:24PM +0000, Richard Purdie wrote:
> On Fri, 2012-03-09 at 14:39 -0700, Tom Rini wrote:
> > Hey all,
> > 
> > Over in meta-ti I kicked off a discussion
> > (https://lists.yoctoproject.org/pipermail/meta-ti/2012-March/000779.html)
> > about if we should be using '?=' or '+=' with IMAGE_FSTYPES in the
> > machine conf files.  This has been discussed a little bit before
> > (http://thread.gmane.org/gmane.comp.handhelds.openembedded.core/2060/focus=2061).
> >  The problem is we have the following and I believe ultimately
> > conflicting use cases:
> 
> I've been under the impression that we decided upon:
> 
> > - The machine needs to say 'I need or support the following formats'
> 
> so the machine starts and sets:
> 
> IMAGE_FSTYPES = "xxxx"
> 
> > - The distro needs to say 'I always want format X'
> 
> so the distro can do:
> 
> IMAGE_FSTYPES += " yyy"
> 
> > - The user needs to say 'I know best, give me only format X'
> 
> So the user can do:
> 
> IMAGE_FSTYPES = "X"

Richard,

Since local.conf gets parsed before machine.conf and distro.conf, the user 
needs to do this override:

IMAGE_FSTYPES_local = "X"

Otherwise machine.conf will always overwrite it with "xxxx" with its 
unconditional assignment.

-- 
Denys


> > - The user needs to say 'I know best, give me what you support + X'
> 
> IMAGE_FSTYPES += " X"
> 
> > We achieve this today, but not very nicely.  For the last one you need
> > to start playing order of operations games and that's just not nice.
> > My suggestion is that we need to change what the machine.conf sets to
> > another variable (SOMETHING_IMAGE_FSTYPES), and a default
> > IMAGE_FSTYPES becomes ?= ${SOMETHING_IMAGE_FSTYPES}.  Distros, and
> > users can then work more easily with their use cases.  Comments?
> 
> I think this is overcomplicating things. Yes the order is important but
> lets just document the above?