Re: [PATCH] Make barebox flashable image link for "multi-image" targets

[Sascha Hauer <s.hauer@pengutronix.de>]

On Thu, Oct 22, 2015 at 06:48:54PM +0000, Trent Piepho wrote:
> On Thu, 2015-10-22 at 09:06 +0200, Sascha Hauer wrote:
> > > > > It only works when a single image is made.  If one is making multiple
> > > > > images, then the concept of a single finished image no longer applies,
> > > > > and no link is made.
> > > > 
> > > > Can't you make the image a config option in buildroot? Depending on only
> > > > having a single image selected in barebox doesn't sound like a good
> > > > idea.
> > > 
> > > buildroot doesn't have an option that for that.  It uses
> > > barebox-flash-image if it exists and then falls back to barebox.bin.
> > > The latter will still exist in a multi-image build, but is not the
> > > correct file!
> > > 
> > > My first thought was to add an option to buildroot for the name of the
> > > flash image file.  But barebox is the one choosing this name and it
> > > knows what it is.  So why should I have to manually copy this data out
> > > of barebox and into buildroot and keep to up to date when it chages?
> > > Barebox knows the value, have it tell buildroot what it is.  And there
> > > is already the barebox-flash-image symlink system that does just this.
> > > This way buildroot (and any other buildsystem or flash or test script
> > > that uses a barebox image) gets told what file to use straight from the
> > > authoritative source: the barebox build system that made the file.
> > > 
> > > So, that's why I did it this way.  And it's not like I'm adding a new
> > > feature for this, just making an existing one work in more cases that it
> > > did before.
> > 
> > Yes, it works in more cases, but not in all. With your patch it works
> > exactly in the case when one board is selected. Once you intentionally
> > or by accident enable another board then buildroot would silently fall
> > back to barebox.bin and nothing works anymore. Some images do not even
> > have a separate config option, for example there are three nitrogen 6x
> > images which are all controlled by the CONFIG_MACH_NITROGEN6X option.
> > 
> > Applying a band aid solution only lowers the pressure to do the
> > necessary changes in buildroot. I am not a fan of this.
> 
> So should the existing support for barebox-flash-image for
> non-multi-image boards be removed too?  If they switch a multi-image
> based build, even if they support only one image, the link goes away as
> you described above and one has the same problem.
> 
> And putting an option into barebox (and also every other script or
> system that wants to do something with the barebox flash image), still
> has the problem of duplicating information.  It's like putting an
> identical #define in two C files instead of in one header that both use.
> Barebox chose the image name, why not have it provide that information
> automatically?
> 
> For instance, I have a script that puts barebox on an SD card.  I have
> multiple different barebox builds for different devices.  I can point
> the script at the barebox output dir and it can tell, because barebox
> provides that information, what image file it needs to flash even
> through the name isn't the same for the different builds.
> 
> 
> What if, in the case of multiple images, the link is still made, but
> points to a non-existent location like
> "multiple-flash-images-generated".  That way anyone using the link will
> get an error and know they need to come up with a different plan.  Like
> not building multiple images when they only want one.
> 
> Another alternative would be to create a file that lists the images
> generated one per line, like the final make output that lists them to
> stdout.  Then the image name(s) could be retrieved automatically even in
> the case of multiple images.

I like this last idea. This would allow to get a consistent behaviour
between single image and multi image builds.

Sascha

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