Add an --ondemand flag to the offload daemon's restore subcommand to
support the post-copy mechanism from the live migration protocol.
In on-demand mode, the daemon creates empty memfds to back the guest
memory and sends them over to the VMM. This lets the VM start quickly,
right after the memfds are mapped into CH's address space.
At runtime, when the guest accesses a page (or the prefault handler
requests it), the daemon faults it in by copying the page content into
its shared memory mapping, then replies to the PageFault request so the
VMM can consider the page present.
Signed-off-by: Sebastien Boeuf <sboeuf@meta.com>
Assisted-by: Claude:claude-opus-4-7
Copy only populated extents when writing the snapshot file and when
filling the restore memfd, leaving unwritten ranges as holes. Both
the on-disk snapshot and the restored guest RAM stay sparse, so that
untouched guest pages cost no disk space or host memory.
This brings the offload daemon closer to be at feature parity with CH's
internal implementation of snapshot/restore. The only missing piece is
on-demand paging at this point.
Signed-off-by: Sebastien Boeuf <sboeuf@meta.com>
Assisted-by: Claude:claude-opus-4-7
Adding a new dedicated binary that is meant to be used as a reference
implementation for validating that offloaded snapshot/restore works and
meant to be used through tests in general.
Signed-off-by: Sebastien Boeuf <sboeuf@meta.com>
Assisted-by: Claude:claude-opus-4-7
