[OE-core] do_image: Adding support for IMAGE_ROOTFS_EXCLUDE_PATH.

[Kristian Amlie]

Ping. Would be great to get some feedback so I can continue working on this.

--
Kristian

On 26/04/17 17:03, Kristian Amlie wrote:
> This is a direct followup from the earlier f6a064d969f414 commit in wic. It
> works more or less the same way: The variable specifies a list of directories
> relative to the root of the rootfs, and these directories will be excluded from
> the resulting rootfs image. If an entry ends with a slash, only the contents are
> omitted, not the directory itself.
> 
> This is early feedback call, and several things are missing here (see
> below). However, I would like to know if at least the basic approach is
> acceptable. Reviewers pressed on time really only need to look at the topmost
> hunk as well as the last couple of lines of the two functions. Those show what
> the basic idea is.
> 
> What's missing:
> 
> * Documentation
> 
> * Test coverage
> 
> * Respecting IMAGE_ROOTFS_EXCLUDE_PATH is a behavior change, and isn't
>   appropriate for all image creators. In fact, for the the main use case [1] to
>   work it must not always be respected.
> 
> My idea for the last point is that the variable will not be respected by
> default, and each of the pure filesystem image creators (btrfs, ext2/3/4, etc)
> will set a flag that mark their image creator as a "pure filesystem", which
> would respect this variable. Image creators that make partitions, however,
> should not respect it, because they will use wic for that purpose instead, and
> then they need to have access to the entire rootfs. Hence they should not set
> the flag.
> 
> I'm imagining something like this:
> 
>   d.setVarFlag('do_image_%s' % t, 'respect_exclude_path', '1')
> 
> although I'm not sure if that's the best approach (tips are welcome).
> 
> [1] The use case for this feature is the following: We are creating two types of
> images in Mender: One complete partitioned image, and one image containing only
> the rootfs. In order to be able to populate non-rootfs partitions, we want to
> use the regular bitbake recipes for building these components, but then exclude
> certain directories from the rootfs image. Using wic, we are adding those
> directories back into the partitioned image, but under different
> partitions. Unlike the rootfs image, the other partitions are not expected to be
> rebuilt after the first rollout.
>