Hello Community Members  , 

 

I would like to propose a change to how we handle sparse image generation for ext* file-systems in OpenEmbedded, 

specifically moving away from the generic img2simg tool toward the specialised ext2simg in the e2fsprogs [contrib/android]

1) Problem

Currently, image_types_sparse.bbclass uses img2simg for all file-system types. 

img2simg is a  tool that reads the raw image to find zero-filled blocks. 

For ext* file-systems, this is inefficient compared to  ext2simg from e2fsprogs [contrib/android]

which understands the file-system structure and uses the block bitmap to determine sparse areas.

2) History

Previously, 'ext2simg' was bundled within android-tools (v5.1 and older).

The utility has since migrated to the e2fsprogs project (contrib/android).

However, upstream e2fsprogs does not provide a build system for this tool,

and it requires libsparse from android-tools to compile.

 

 

3) Proposed Changes

To implement this, I am looking at a cross-layer approach:

 

a. meta-oe (android-tools):

Export libsparse, libbase, and liblog headers and libraries to the sysroot. Currently, these are often internal to the build.

Reorganise header installation to ${includedir}/sparse to match the expected include paths for e2fsprogs contrib tools.

 

b. oe-core (e2fsprogs):

Add a conditional compilation step in e2fsprogs-native to build the ext4sparse utility located in contrib/android/.

This would link against the exported libsparse from android-tools-native.

 

c. meta-oe (image_types_sparse.bbclass):

Update CONVERSION_CMD:sparse to detect ext* types.

Use  ext2simg from the e2fsprogs [contrib/android] for these types while falling back to img2simg for others (like f2fs).

 

 

4) Points for Discussion / Feasibility

     I am seeking feedback on the following:

 

a. Layer Dependency: 

This introduces a tighter coupling between oe-core and meta-oe. 

Is it acceptable for e2fsprogs-native (core) to optionally depend on android-tools-native (meta-oe), 

or i can create an bbapend file in meta-oe called e2fsprogs_%.bbappend.