mkfs.ext4 zeroes the entire inode table and journal at format time
unless told otherwise. On an 8 GiB work disk that's roughly 500-700ms
of host CPU/IO per 'banger vm create', for a one-time small per-write
penalty inside the guest the first time it touches an unwritten
inode that nobody can perceive.
Centralise the canonical mkfs -E option list as
system.MkfsExtraOptions and use it everywhere banger calls mkfs.ext4
on a VM-internal image: the no-seed work disk, MaterializeWorkDisk,
BuildWorkSeedImage, and the imagepull rootfs builder. The work-disk
paths feed vm create directly; the others are one-off but still
benefit from the faster format.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
The package doc in internal/imagepull/imagepull.go still described
a two-step Pull + Flatten + BuildExt4 pipeline and warned that the
resulting image was "suitable as input to `image build` but not
directly bootable" because ownership preservation was deferred.
That's been wrong for a while: ApplyOwnership
(internal/imagepull/ownership.go) restores tar-header uid/gid/mode
via a debugfs set_inode_field batch, and InjectGuestAgents
(internal/imagepull/inject.go) writes banger's guest-side assets
into the image. `image pull` now produces a directly bootable
rootfs end-to-end.
Updated:
- imagepull.go package doc — describes the full
Pull → Flatten → BuildExt4 → ApplyOwnership → InjectGuestAgents
pipeline and drops the "Phase A limitations" list that spoke
of deferred ownership.
- ext4.go BuildExt4 doc — notes that the filesystem is root-owned
via `-E root_owner=0:0` and points at ApplyOwnership as the
step that handles per-file ownership, instead of the previous
"see the package doc for the implications" handwave.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
mkfs.ext4's positional fs-size is documented in 1 KiB units (not the
filesystem's 4 KiB block size), so passing sizeBytes/4096 made
filesystems 1/4 the intended size. A 4 GiB request became a 1 GiB
ext4 in a 4 GiB file, packed to 0 free blocks — VM create then failed
with 'Could not allocate block' when patchRootOverlay tried to write
guest config.
The file is truncated to the target size before mkfs runs; without
the positional arg, mkfs uses the whole device.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
New internal/imagepull/ subpackage. Three concerns, each
independently testable:
Pull (imagepull.go):
- github.com/google/go-containerregistry's remote.Image with the
linux/amd64 platform pinned. Anonymous pulls only for v1.
- Layer blobs cached on disk via cache.NewFilesystemCache under
<cacheDir>/blobs/sha256/<hex> — OCI-standard layout so
skopeo/crane could co-exist later.
- Eagerly touches every layer once so network errors surface at
Pull time, not deep in Flatten.
Flatten (flatten.go):
- Replays layers oldest-first into destDir.
- Whiteout-aware: .wh.<name> deletes the named entry,
.wh..wh..opq wipes the parent directory's contents from prior
layers.
- Path-traversal hardening mirrored from kernelcat extractTar:
reject .., absolute paths, and symlinks/hardlinks whose
resolved target escapes destDir.
- Handles tar.TypeReg, TypeDir, TypeSymlink, TypeLink. Skips
device/fifo nodes silently (need privilege; udev/devtmpfs
handles them in the guest).
BuildExt4 (ext4.go):
- Truncates outFile to sizeBytes, then runs `mkfs.ext4 -F -d
<srcDir> -E root_owner=0:0`. No mount, no sudo, no loopback.
- 64 MiB floor; callers handle real sizing with content-aware
headroom.
- File ownership in the resulting ext4 reflects srcDir's on-disk
ownership — runner's uid/gid since extraction was unprivileged.
Documented in package doc as a Phase A v1 limitation; Phase B
will add a debugfs- or tar2ext4-based ownership fixup.
paths.Layout gains OCICacheDir at $XDG_CACHE_HOME/banger/oci/,
ensured at startup alongside the other dirs.
Tests use go-containerregistry's in-process registry to push and
pull synthetic multi-layer images. Cover: layer caching round-trip,
whiteout + opaque-marker handling, path-traversal rejection, unsafe
symlink rejection, real mkfs.ext4 round-trip (skipped if mkfs.ext4
absent), and tiny-size rejection.
go-containerregistry v0.21.5 added as a direct dep, plus its
transitive closure (containerd/stargz, opencontainers/go-digest,
docker/cli config helpers, etc).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
