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docs: Plan H — per-layer ZFS clone chain for daemon URIs (dockerd://, podman://) - #20
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sodre wants to merge 2 commits into
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docs: Plan H — per-layer ZFS clone chain for daemon URIs (dockerd://, podman://)#20sodre wants to merge 2 commits into
sodre wants to merge 2 commits into
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Plan H extends Plan G's per-layer zfs clone chain to dockerd:// and
podman:// URIs via \`${engine} save\` (preserves per-layer tarballs +
manifest.json describing layer order) instead of \`${engine} export\`
(flattens). Layer digests are content-addressed via sha256 of each
layer.tar, so the same image won't share .layers/ datasets across
docker:// and dockerd:// sources (registry blobs are compressed; save's
layer.tar is uncompressed — same content, different sha) but multiple
local daemon images with shared base layers DO dedup at the .layers/
level.
Default-off — flag unset leaves the existing flat-export daemon path
byte-for-byte unchanged. Same dispatch shape as Plan G (chain-mode
gate on ENROOT_ZFS_LAYER_CHAIN=y, branched in import_daemon_pointer
and create_from_pointer's recovery arm).
Plan-doc only — depends on Plan G's helpers, which land in PR #17.
The doc/plans/README.md index and doc/zfs.md knob description will
follow when both Plan G and Plan H land on zenroot/main.
Signed-off-by: Patrick Sodré <patrick@zero-ae.com>Signed-off-by: Patrick Sodré <patrick@zero-ae.com>
sodre
marked this pull request as ready for review
May 6, 2026 12:19
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Follow-up to #17 (Plan G). Adds the implementation plan for extending chain mode (
ENROOT_ZFS_LAYER_CHAIN=y) to daemon-local image URIs.Why a follow-up plan
Plan G (#17) only handles
docker://URIs because they go throughdocker::_prepare_layerswhich produces the per-layer directories the chain installer needs. The daemon path (dockerd://,podman://) uses${engine} export | tar -x— a flatten operation that drops layer information, so chain mode is silently a no-op for daemon URIs today.Plan H bridges that gap by switching the daemon path's extraction from
${engine} exportto${engine} save(which preserves per-layer tarballs in a tar archive plus amanifest.jsondescribing layer order), then routing through Plan G's existing_install_layer_chain.Tradeoffs spelled out in the plan
${engine} save | tar -xdumps each layer'slayer.tarto disk before extraction, so peak disk is ~1× the merged image size. Today's flat-export streams in a single pass with effectively no intermediate.docker://alpineand the same layer extracted viadockerd://alpineproduce different.layers/<digest>datasets — the registry blob is gzip/zstd-compressed anddocker save'slayer.taris uncompressed, so the sha256s differ. Within-source dedup (multiple daemon images that share a base) still works.podman save --format oci-archive) is not in scope.What lands in this PR
Plan markdown only —
doc/plans/2026-05-06-zfs-h-daemon-chain.md. The implementation references Plan G's_install_layer_chain/_apply_layer_payload/_build_layerhelpers, so this plan is unblocked once Plan G (#17) merges.Status
Draft — not for merge yet. Plan G (#17) should land first. The README/zfs.md cross-references will follow when both have landed.
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