Sync framework extensibility

Embodiments described herein may involve enabling applications to cooperate with a system-level sync framework. The sync framework may provide system synchronization of files between user devices and a cloud storage service. Arbitrary applications on a user computing device can communicate with the sync framework to temporarily suspend synchronization of a specified file by the sync framework. The application can register functions with the sync framework that the sync framework can invoke in relation to suspending synchronization, continuing to provide system-level access to the file for arbitrary applications, and resuming synchronization.