The talk was about a new file system called ComposerFS, which is designed for read-only images, such as those used in container hosts or for OSTree verified boot. The file system works by hashing files and storing them in a repository format. The talk explained how ComposerFS works in conjunction with OSTree and how it can be used to protect against runtime verification. It also mentioned possible use cases for ComposerFS, such as opportunistic sharing of files in containers. The speaker compared the performance of ComposerFS with other solutions and also discussed potential improvements to the OverlayFS and EROFS file systems. During the Q&A session, the speaker addressed questions about the compatibility of ComposerFS with the OCI image format and its suitability for remote build systems.