[OE-core] Contents of non-rootfs partitions

[Kristian Amlie]

On 24/11/16 07:15, Ulrich Ölmann wrote:
> Hi,
> 
> On Wed, Nov 23, 2016 at 04:56:56PM +0100, Patrick Ohly wrote:
>> On Wed, 2016-11-23 at 15:22 +0200, Ed Bartosh 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:
>>>>> [...]
>>>>> 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 prefer the explicit --exclude-dirs. It's less surprising and perhaps
>> there are usages for having the same content in different partitions
>> (redundancy, factory reset, etc.).
>>
>> Excluding only the directory content but not the actual directory is
>> indeed a good point. I'm a bit undecided. When excluding only the
>> directory content, there's no way of building a rootfs without that
>> mount point, if that's desired. OTOH, when excluding also the directory,
>> the data would have to be staged under a different path in the rootfs
>> and the mount point would have to be a separate, empty directory.
>>
>> I'm leaning towards excluding the directory content and keeping the
>> directory.
> 
> what about having both possibilities by leaning against the syntax that rsync
> uses to specify if a whole source directory or only it's contents shall be
> synced to some destination site (see [1])?
> 
> In analogy to this to exclude only the contents of the directory named 'data'
> you would use
> 
>   --exclude-dirs data/
> 
> but to additionally exclude the dir itself as well it would read
> 
>   --exclude-dirs data

This is creative, but ultimately too unintuitive IMHO. Rsync is the only
tool which uses this syntax AFAIK, and it's a constant source of
confusion, especially when mixed with cp or similar commands.

There is some discussion in the ticket as well:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=10712

-- 
Kristian