Maksym Pavlenko 1e001e6dfe erofs: make the layer content cache work with parallel unpack ...

The cache used to serve a hit by committing the layer during Prepare and
returning ErrAlreadyExists, which is incompatible with parallel unpacking:
the "rebase" capability defers the parent to Commit time, so a
commit-at-Prepare layer ends up parentless. The erofs snapshotter therefore
had to disable rebase whenever the cache was enabled, making every cache
*miss* fall back to a fully sequential (slower-than-cold) pull.

Introduce snapshots.ErrAlreadyStaged, returned from Prepare to mean "the
active snapshot's content is staged; skip the layer download and apply, but
still Commit it" (where the parent is applied). Unlike ErrAlreadyExists it
does not end the layer's lifecycle. The unpacker handles it by emitting a
status whose bottom half runs the normal serialized commit (rebasing the
parent in), and the metadata snapshotter threads it through Prepare like a
normal active snapshot. The erofs cache hit now stages the blob and returns
ErrAlreadyStaged instead of committing, so it can advertise "rebase"
unconditionally: hits skip download+conversion and misses stay parallel.

Also promote the "rebase" capability string to snapshots.RebaseCap (shared by
the unpacker, erofs, and overlay).

Follow up:  fetch is range-based, so only a fully cached contiguous
prefix skips downloads; a miss in a lower layer still pulls everything above
it. Per-layer fetch-skip is left as a follow-up.

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

2026-07-31 09:18:15 -07:00

..

plugin.go

erofs: make the layer content cache work with parallel unpack

2026-07-31 09:18:15 -07:00