[OE-core] Consistency and use cases for IMAGE_FSTYPES

[Tom Rini]

On Fri, Mar 23, 2012 at 09:17:20AM -0700, Darren Hart wrote:
> On 03/23/2012 08:48 AM, Tom Rini wrote:
> > On Fri, Mar 23, 2012 at 01:14:24AM +0000, Richard Purdie wrote:
> >> On Thu, 2012-03-22 at 19:53 -0400, Denys Dmytriyenko wrote:
> >>> 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"
> >>>
> >>> 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.
> >>
> >> Right, I'd forgotten that little detail :/.
> >>
> >> It actually makes me wonder if our include order is the right one but
> >> now isn't the time to try changing that.
> >>
> >> I agree the neatest way to change it is probably something like
> >> MACHINE_FSTYPES. I do worry a lot about backwards compatibility though
> >> and I'd also point out where we're at in the release cycle (bug fix
> >> only).
> > 
> > Well, one problem that would make this a bugfix is that no one does what
> > you say we agreed on today.  oe-core has qemu.inc using ?=, meta-intel
> > is using += and meta-ti is mixed (which is what got this started).
> > 
> > 
> 
> Is this causing any nasty failures right now, or is it in the "this is a
> confusing mess and it would be nice to get it cleaned up" bucket? If the
> latter, I think I'd prefer to wait a bit an clean up the
> local.conf/machine.conf IMAGE_FSTYPES clobbering issue.

Well, I found this as part of adding UBI support for a board and it
wasn't sticking.

I'd go so far as to say that for a release, we really need to pick a
standard, document and follow it.  If it's machine.conf does =, everyone
else does += and user's have to do _local =, fine, it sucks but it's
documented and consistent on all of the BSP layers.

> If this isn't really fixable (for whatever requirements bitbake has on
> load/parse order of config files), then Koen's EXTRA_IMAGE_FSTYPES seems
> like the most consistent mechanism with other things, like
> CORE_IMAGE_EXTRA_INSTALL (OK, maybe IMAGE_EXTRA_FSTYPES ?).
> 
> So the default becomes:
> 
> IMAGE_FSTYPES ?= ${IMAGE_EXTRA_FSTYPES}
> 
> and DISTROs might define that as:
> 
> IMAGE_FSTYPES += "yyy"
> 
> and users can update local.conf to be:
> 
> IMAGE_FSTYPES = "X"
> 
> But, doesn't this meant the DISTRO append will still change the
> IMAGE_FSTYPES to "X yyy" even though the user intended "only X"?

How about:
bitbake.conf: IMAGE_FSTYPES ??= ${IMAGE_EXTRA_FSTYPES}
distro.conf: IMAGE_FSTYPES ?= "yyy ${IMAGE_EXTRA_FSTYPES}"
local.conf: IMAGE_FSTYPES = "X"

Or am I forgetting the magic of ??= again...

-- 
Tom
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