imidj (pronouced like "image") is a tool like casync but simpler as it focuses only on chunking and re-assembling chunks into images again.
- glib
- liblzma
- libcrypto
- libcurl
Indexing is the operation that takes a image (such as a rootfs for an embedded device), splits it into variable-sized chunks using a rolling hash function, and saves the compressed chunks to disk (.chblo.xz). It also writes a chunk-index file (.chidx) that lists the chunks in order for re-assembly.
The indexing operation is usually performed by a CI system or by a release manager.
imidj is format agnostic, but to achieve small deltas between image versions, it is recommended to use a techniques such as reproducible builds.
Example:
imidj index myimage-v3.squashfs output-dir
indexes myimage-v3.squashfs and writes myimage-v3.squashfs.chidx to output-dir. The chunks are written to etc: output-dir/chunks/de/deadbeefdeadbeef.chblo.xz.
By serving the output-dir via HTTP/HTTPS/FTP/..., the patch operation can download the chunks remotely.
Patching is the operation that takes the chunk-index file (.chidx) and a URL to re-assemble the image. By feeding the patch operation one or more images (and their corresponding .chidx) already present on the target, it can then re-use chunks present in these local reference images, and only download chunks not found locally.
The patching operation is typically performed on a target device to upgrade/downgrade the rootfs and kernel.
Example:
imidj patch myimage-v3.squashfs myimage-v3.squashfs.chidx -u http://server:port/ -r myimage-v1.squashfs.chidx -R myimage-v1.squashfs -r myimage-v2.squashfs.chidx -R myimage-v2.squashfs
will create or update myimage-v3.squashfs based on the information in the chunk-index file myimage-v3.squashfs.chidx, reusing any chunks already found in myimage-v1.squashfs or myimage-v2.squashfs, and downloading any chunks not present in the former from the URL http://server:port/.