Re: [ptxdist] PTXdist usescases

["Baeuerle, Florian" <Florian.Baeuerle@allegion.com>]

Am Dienstag, den 28.08.2018, 17:27 +0200 schrieb Erwin Rol:
> Hey Michael,
> 
> On Mon, 2018-08-27 at 18:40 +0200, Michael Olbrich wrote:
> > On Mon, Aug 13, 2018 at 02:40:14PM +0200, Robert Schwebel wrote:
> > > On Mon, Aug 13, 2018 at 02:16:20PM +0200, Erwin Rol wrote:
> > > > > Michael Olbrich prototyped a layering system for ptxdist
> > > > > we are currently testing the prototype and mol
> > > > > will post it here on the mailing list afterwards.
> > > > > 
> 
> What I am really looking for is to be able to make two (or more)
> filesystem images that I can build (and version) independently, and
> where the next "layer" does not have to rebuild the previous layer.
> 
> For example;
> 
> - A rootfs layer that generates a rootfs image, which holds the minimal
> setup for the hardware (bash, systemd, etc).
> 
> - A qt5fs, which holds QT5 and gui stuff, but that does not need to
> build the stuff that is already in the rootfs image (like bash and
> systemd).
> 
> - A appfs that holds own applications that use QT5 but again without
> building qt5fs/rootfs.

The advantages of such a scheme would be smaller updates.

On the other hand, you have to keep the upper layers (rootfs and qt5fs)
stable. This would probably lead to a reduced frequency of updates in those
layers.

Anyway, this might actually be possible with image packages[1], if you set
IMAGE_XPKG_EXTRA_ARGS to "--nodeps" (or find a different way to pass that
option to opkg). You can basically build an image with just the Qt5-package.

But then you'd have to make sure on your own, that the rootfs-image contains
all the dependencies required. Otherwise, you could pick Qt5s dependencies that
are not already included in the rootfs-image. This is where it gets hairy I
think.


I personally prefer just having one rootfs, because its simple and robust.
The problem is the size of updates, but the largest project's rootfs is only
roughly 50 MiB (including qt5, noto fonts and application). Other projects'
rootfs images are below 20 MiB (includes the kernel).

You can just update ptxdist and get new versions of everything without
thinking about it too much.

Regarding build times: You usually only build the whole thing once, and
then just recompile only the application anyway.
In our CI, a full build from scratch takes roughly 8 minutes for the largest
rootfs image.


1: https://www.ptxdist.org/doc/ref_manual.html#image-packages


Regards
Florian
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