[OE-core] Contents of non-rootfs partitions

[Ed Bartosh]

On Wed, Nov 23, 2016 at 02:08:28PM +0100, Kristian Amlie wrote:
> On 23/11/16 13:08, Ed Bartosh wrote:
> > On Tue, Nov 22, 2016 at 12:54:52PM +0100, Kristian Amlie wrote:
> >> On 22/11/16 12:10, Patrick Ohly wrote:
> >>>> ...
> >>>
> >>> All of these introduce some special mechanism. Let me propose something
> >>> that might integrate better with the existing tooling:
> >>>
> >>> The "rootfs" directory gets redefined as representing the entire virtual
> >>> file system. When creating a disk image, it gets split up into different
> >>> partitions based on the image configuration.
> >>>
> >>> For example, the /home or /data directories in the rootfs could hold the
> >>> content that in some image configurations goes into separate partitions.
> >>>
> >>> The advantage of this approach is that the tooling for staging content
> >>> for image creation does not need to be changed. The same staged content
> >>> then can be used to create different images, potentially even using
> >>> different partition layouts.
> >>
> >> That's a very good idea. I think it beats all of my suggestions!
> >>
> >>> To implement this approach with wic, wic needs to be taught how to
> >>> exclude directories from the main rootfs. Ideally, the mkfs.* tools
> >>> should also support that without having to make an intermediate copy of
> >>> the files for a certain partition, but initially wic could create
> >>> temporary directory trees.
> >>
> >> Yes, some work would be needed here, but ultimately it would be contained within wic and related tools, which is a good thing.
> >>
> > 
> > I support the idea. Let's discuss the details of implementation and
> > create a bug in bugzilla to track the development 
> 
> Do you want me to create the ticket? (it'll be my first, so apologies in
> advance if I omit something important)
> 
> > This can be done by extending existing rootfs plugin. It should be able
> > to do 2 things:
> > 
> > - populate content of one rootfs directory to the partition. We can
> >   extend syntax of --rootfs-dir parameter to specify optional directory path to use
> > 
> > - exclude rootfs directories when populating partitions. I'd propose to
> >   introduce --exclude-dirs wks parser option to handle this.
> > 
> > Example of wks file with proposed new options:
> > part /     --source rootfs --rootfs-dir=core-image-minimal       --ondisk sda --fstype=ext4 --label root --align 1024 --exclude-dirs data --exclude-dirs home
> > part /data --source rootfs --rootfs-dir=core-image-minimal:/home --ondisk sda --fstype=ext4 --label data --align 1024
> > part /home --source rootfs --rootfs-dir=core-image-minimal:/data --ondisk sda --fstype=ext4 --label data --align 1024
> > 
> > Does this make sense?
> 
> Looks good. The only thing I would question is that, in the interest of
> reducing redundancy, maybe we should omit --exclude-dirs and have wic
> figure this out by combining all the entries, since "--exclude-dirs
> <dir>" and the corresponding "part <dir>" will almost always come in
> pairs. Possibly we could mark the "/" partition with one single
> --no-overlapping-dirs to force wic to make this consideration. Or do you
> think that's too magical?
>
Tt's quite implicit from my point of view. However, if people like it we
can implement it this way.

> (I haven't checked how feasible this is in the code btw)

I think it would be much easier to implement --exclude-dirs.

BTW, it will also allow to exclude directories from any partition, not just from
root, e.g. to use --exclude dirs this way:
part /data --source rootfs --rootfs-dir=core-image-minimal:/home --ondisk sda --fstype=ext4 --label data --align 1024 --exclude-dirs cache --exclude-dirs tmp

--
Regards,
Ed