Re: [PATCH 1/2] blspec: allow board files to overwrite config file settings

[Sascha Hauer <sha@pengutronix.de>]

On Tue, Jan 19, 2021 at 12:42:08PM +0100, Marco Felsch wrote:
> Hi Sascha,
> 
> On 21-01-19 12:01, Sascha Hauer wrote:
> > Hi Marco,
> > On Mon, Jan 18, 2021 at 09:48:49PM +0100, Marco Felsch wrote:
> > > This commit adds the support to overwrite and/or adapt blspec config
> > > files by the following global variables:
> > >   - global.blspec.fixup.devicetree
> > >   - global.blspec.fixup.initrd
> > >   - global.blspec.fixup.options
> > >   - global.blspec.fixup.linux
> > >   - global.blspec.fixup.devicetree-overlay.
> > > 
> > > Overwriting blspec-config's shouldn't be the normal case but there are
> > > cases where this support is needed. One use-case can be a special
> > > handling during update. E.g. the normal boot-flow don't need the initrd
> > > but the update-flow uses it because the update system is on the initrd.
> > 
> > When you have an update system and a regular system on the same
> > filesystem then I would expect an additional bootspec entry for the
> > update system.
> 
> AFAIK, barebox tries to find the correct entry by checking all config
> files and loads the first matching config file. Is there a way to
> specify an explicite config file?

Not yet, but maybe we are at a point where a way should be added.

> 
> > > Another use-case could be a dynamic devicetree-overlay handling. E.g.
> > > the board code dynamically checks which periphery boards are connected
> > > and adds the required overlays dynamically.
> > 
> > Board code can register overlays already, there's no need for bootspec
> > to do that.
> 
> But this needs a lot more handling if we boot from nfs or from emmc.
> Therefore I utilized the already existing code :)

I'm not sure I understand you correctly. You probably mean that you have
to decide which overlay to use when the path to the rootfs is already
known, right?

> 
> > Overall overwriting bootspec variables somewhat contradicts the whole
> > purpose of bootspec. I don't like that very much, so you'll need very
> > good reasons to get this through ;)
> 
> Yep, I thought so ;) Therefore I wrote a big warning. It gives you a lot
> opportunities to shot yourself in the foot. Therefore I print a warning
> if you overwrite a already exisiting config.

Your code shouldn't issue a warning when it's exactly used like
intended. A warning tells people they are doing something wrong, but in
this case they are doing everything correctly, so they might be tempted
to just patch the warning away.

Sascha

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