Erofs overlay patches

[martinp26]

disk: honor erofscompression and allow create options for the overlay read-only root fs

Issue#3038
Issue#3039

What

Two commits fixing/extending compression handling for the overlayroot
read-only filesystem:

1. disk: honor erofscompression for overlay read-only root filesystem
   The overlay read-only fs can be squashfs or erofs
   (overlayroot_readonly_filesystem), but both overlay code paths in
   DiskBuilder hard-coded get_squashfscompression(), so
   erofscompression was ignored and an erofs overlay base was written
   uncompressed. Routes the read-only compression through a small helper
   (_get_root_readonly_compression) that returns get_erofscompression()
   for an erofs read-only type and get_squashfscompression() otherwise.
   Complements Add missing erofscompression validation #2648 (which fixed only the standalone erofs builder).

2. disk: allow extra create options for the overlay read-only root fs
   Adds a new free-form overlayroot_readonly_createoptions attribute
   (whitespace-split, analogous to fscreateoptions) passed as
   create_options to both overlay read-only FileSystem builds. This
   lets a description request e.g.
   overlayroot_readonly_createoptions="-C 1048576" for a larger EROFS
   pcluster. Updates schema (rnc + rng), the generated xml_parse.py,
   XMLState.get_fs_readonly_create_option_list(), disk.py, docs and
   tests.

Why

Building an AL2023 overlayroot EROFS image, erofscompression had no
effect (uncompressed ~1.4 GB base). With these two changes the recipe can
use erofscompression="lz4hc,level=12" +
overlayroot_readonly_createoptions="-C 1048576" directly.

Testing

• make check — flake8 clean (shell unchanged)
• make test — mypy kiwi clean; full unit suite passes at 100%
  coverage (new code covered; existing overlay test updated)
• make docs — sphinx html builds, new attribute documented
• schema regeneration verified: trang reproduces kiwi.rng
  byte-for-byte from the edited kiwi.rnc; the generated xml_parse.py
  additions match the generateDS output pattern

Assisted-by: Kiro:claude-opus-4.8

[schaefi]

Thanks much for looking into this.

I don't think we need a new attribute to differentiate compression options for erofs between different image layouts. The schema already provides k.type.erofscompression.attribute. So it should be possible to utilize this in the same way as it was done for builder/live.py and builder/filesystem.py. Just add the missing part to builder/disk.py as you you did but without the need for a new attribute in the schema

Thoughts ?

[schaefi]

use erofscompression="lz4hc,level=12" + overlayroot_readonly_createoptions="-C 1048576" directly.

under which condition you would need to specify both for one image type ?

[schaefi]

From my perspective you only need to apply the code we have in the other builders

filesystem_custom_parameters.update( 
    {
        'compression':
            self.xml_state.build_type.get_squashfscompression()
    } if root_filesystem == 'squashfs' else {
        'compression':
            self.xml_state.build_type.get_erofscompression()
    }
)

to the builder/disk.py where we only have

custom_args={
    'compression':
        self.xml_state.build_type.get_squashfscompression()
}

at several places

[martinp26]

use erofscompression="lz4hc,level=12" + overlayroot_readonly_createoptions="-C 1048576" directly.

under which condition you would need to specify both for one image type ?

mkfs.erofs carves out -C max-pcluster-size as a distinct setting from -z compression-algorithm[,#][:...] and there are potentially more options that one may want to pass to mkfs.*. fscreateoptions is used for the RW layer, overlayroot_readonly_createoptions would be the equivalent for the RO layer.

I am not seeing a way to express that with today's schema, am I missing it?

[schaefi]

@martinp26 ok, sorry I was on the wrong track. Yes makes perfect sense as we are using erofscompression specifically for compression settings and there is nothing that handles filesystem creation options for the read-only filesystem in an overlay build.

All good, sorry for the noise

[schaefi]

Looks good 👍

[schaefi]

I will build Staging packages at

https://build.opensuse.org/project/show/Virtualization:Appliances:Staging

[martinp26]

Thanks!