[Buildroot] Parallel top-level make and multiple rootfs types

[Yann E. MORIN <yann.morin.1998@free.fr>]

Thomas, Arnout, All,

On 2017-11-04 23:05 +0100, Thomas Petazzoni spake thusly:
> On Sat, 4 Nov 2017 21:56:58 +0100, Arnout Vandecappelle wrote:
> > > can I disable parallel execution of the rootfs-* build steps while still
> > > building everything up to target-finalize in parallel?  
> > 
> >  No, that's not possible with make. I don't know if Thomas has already thought
> > about this aspect of top-level parallel...
> 
> No, I haven't thought about this aspect of top-level parallel build.
> 
> >  I think the solution is to change the way we build the rootfs: instead of doing
> > the fakeroot steps over and over again, do it once, save with the -s option, and
> > then do the individual filesystems in a separate (readonly) fakeroot with -i to
> > read the previously created fakeroot file.
> 
> I think Yann did some work in terms of parallel generation of
> filesystem images, but I'm not sure exactly what he did :)

Quite a lot, in fact... See:
    https://git.buildroot.org/~ymorin/git/buildroot/log/?h=yem/fs-3

I wanted to send it earlier, but I did not yet find time to completely
test it...

The runtime-tests infra needed a few tweaks to make it work correctly,
and it also caught a few regressions that I already fixed, but it really
needs a bit more testing I think...

Hopefully I get some time to respin it at the bginning iof next cycle...

Regards,
Yann E. MORIN.

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