[OE-core] Contents of non-rootfs partitions

[Maciej Borzęcki]

On Wed, Nov 23, 2016 at 2:22 PM, Ed Bartosh <ed.bartosh at linux.intel.com> wrote:
> 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

Just to be sure, --exclude-dirs means that the contents of the
directory are skipped, not the directory itself?

Given your example, /home/tmp, /home/cache will be included in /data,
but /home/{cache,tmp}/* not. Is this correct?

Regards,
-- 
Maciej Borzecki
RnDity