Projects/ZFS Channel Programs

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See also slides and video from talk at OpenZFS Developer Summit 2013, and slides and video from the OpenZFS Developer Summit 2014

Proposal

A ZFS channel program (ZCP) is a small script written in a domain specific language that manipulate ZFS internals in a single, atomically-visible operation. For instance, to delete all snapshots of a filesystem a ZCP could be written which 1) generates the list of snapshots, 2) traverses that list, and 3) destroys each snapshot unconditionally. Because each of these statements would be evaluated from within the kernel, ZCPs can guarantee safety from interference with other concurrent ZFS modifications. Executing from inside the kernel allows us to guarantee atomic visibility of these operations (correctness) and allows them to be performed in a single transaction group (performance).

A successful implementation of ZCP will:

  1. Support equivalent functionality for all of the current ZFS commands with improved performance and correctness from the point of view of the user of ZFS.
  2. Facilitate the quick addition of new and useful commands as ZCP enables the implementation of more powerful operations which previously would have been unsafe to implement in user programs, or would require modifications to the kernel for correctness. Since the ZCP layer guarantees the atomicity of each ZCP, we only need to write new sync_tasks for individual simple operations, then can use ZCPs to chain those simple operations together into more complicated operations.
  3. Allow ZFS users to safely implement their own ZFS operations without performing operations they don’t have the privileges for.
  4. Improve the performance and correctness of existing applications built on ZFS operations.