[OE-core] Contents of non-rootfs partitions

[Khem Raj]

> On Nov 22, 2016, at 11:13 PM, Kristian Amlie <kristian.amlie at mender.io> wrote:
> 
> On 23/11/16 00:45, Khem Raj wrote:
>> On 11/22/16 1:05 AM, Kristian Amlie wrote:
>>> Hey
>>> 
>>> In Mender we are using a dual rootfs partition layout (A/B layout) with a persistent data partition on the side. We're using wic to do the actual image building.
>>> 
>>> However, putting files into this data partition is not a straightforward operation ATM. All recipes in OE put files into the rootfs only, and we'd like there to be a way to specify that files should go into the data partition.
>>> 
>>> I haven't seen any straightforward way to do this in OE. Some suggestions for how it could be done:
>>> 
>>> * A "DATA_FILES" variable (like "IMAGE_BOOT_FILES"), where you can list files you'd like to be included. This is very straightforward, but has the disadvantage of being a bit hairy when paths are involved, and it doesn't allow for much logic.
>>> 
>>> * Keep a special "data" directory, something similar to sysroot, where recipes could install files into in order to have it included on the data partition. We could potentially have a bbclass for use in recipes to make this more streamlined.
>>> 
>> 
>> Firstly, it needs to be defined what the data partition is about.
>> 1. is it some pre-initialized/seeded data that can then be modified during
>> subsequent boots ?
>> 2. Is it read-only data which is then used to populate r/w data segments in
>> RAM during boot
>> 3. is it data that does not change over the course of install and reboots of
>> the device
> 
> It's preseeded, but modifiable data, that survives complete rootfs
> updates. IOW if you overwrite either of your A/B rootfs partitions, the
> data partition and its content survives.

at some point this data segment will be seeded.
think of factory case. 

So in such a case updates should not touch them unless user does a factory reset
which should clean it up

> 
> -- 
> Kristian