casync-nano

casync-nano is a feature-reduced replacement for casync aimed at embedded targets. It only supports extract operations, the .caibx file format and limits hashing to SHA256 hashes, but in turn tries to be light on dependencies and system resources in operation.

It implements enough of the regular casync CLI to work as a drop-in replacement in the casync mode of RAUC.

Scope

casync-nano is meant to be used as part of an image-based differential update mechanism for embedded devices. As such, it leaves out features such as filesystem images (.caidx) and image generation/management. On the other hand, it has some features that the original casync implementation lacks:

• Caching of index files corresponding to a local chunk store ("seed" in casync terminology). This is useful to avoid slow reindexing of a partition in an A/B update scheme where the active partition is read-only and thus corresponds to the index file that created it during the previous update by definition. (Chunks read from such a store are still validated to address unintentional changes and bit rot)
• Support for the kernel crypto API to accelerate hashing operations using hardware mechanisms that are present on many modern SoCs.
• Vastly reduced memory usage

State

casync-nano works and is actively being used. However, it should still be considered alpha-quality software. Many possible optimizations still have to be implemented.

Currently, casync-nano only supports reading from and writing to block devices (such as eMMC storage).

Dependencies

• libcurl
• openssl
• zstd