[OE-core] Contents of non-rootfs partitions

[Kristian Amlie]

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?

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

-- 
Kristian