Hi Stefan, > This looks interesting. I've pondered whether the layered and immutable > image trends in recent years can be used effectively for virtual > machines.
There are already some examples: https://www.databricks.com/blog/booting-databricks-vms-7x-faster-serverless-compute https://community.fly.io/t/experimental-speedy-machine-creation-with-overlaybd/18958 And secure containers, agent sandboxes are special forms of VMs. > The advantage of a block driver is that it has better integration with > QEMU and may avoid the need for privileges. > By the way, I see that overylaybd already supports tcmu-runner, so I > guess you've decided that the benefits of integrating directly into QEMU > are worth it. Yes. > > 4. CLI surface: point -drive at the OCI-style JSON image config > > (which lists the layer blobs), or expose per-layer options? > Both :). Per-layer options allow for run-time (re)configuration or > hotplug using blockdev-add and similar monitor commands. Users may > prefer to point QEMU at a JSON file rather than building long > command-line options. OK > One thing I noticed is that the append-only format used for the upper > write layer is not documented. I guess it's different from the read-only > LSTM format since the index won't be kept in sorted order when > appending. > Do you want to document the append-only format? Yes, I'll document it later. It's only slightly different from the read-only one. Thanks Huiba
