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imagepull: update stale package + BuildExt4 docs

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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>
This commit is contained in:
Thales Maciel 2026-04-23 14:34:25 -03:00
parent 5eceebe49f
commit 2ebd2b64bb
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GPG key ID: 33112E6833C34679
2 changed files with 32 additions and 21 deletions
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12
internal/imagepull/ext4.go
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@ -17,12 +17,14 @@ const MinExt4Size int64 = 1 << 20 * 64 // 64 MiB
// BuildExt4 creates outFile as a sparse ext4 image of sizeBytes and
// populates it from srcDir using `mkfs.ext4 -F -d`. No mount, no sudo.
//
// sizeBytes must be at least MinExt4Size. Callers are expected to size
// the file with headroom over the staged tree (the daemon orchestrator
// does this; this function only enforces a sanity floor).
// sizeBytes must be at least MinExt4Size. Callers size the file with
// headroom over the staged tree (the daemon orchestrator does this;
// this function only enforces a sanity floor).
//
// The resulting image's file ownership reflects srcDir's on-disk
// ownership — see the package doc for the implications.
// The filesystem itself is root-owned via `-E root_owner=0:0`, but
// the per-file uid/gid/mode inside srcDir are the runner's — Go's
// unprivileged tar extraction can't preserve them. The pipeline's
// next step, ApplyOwnership, restores the tar-header values.
func BuildExt4(ctx context.Context, runner system.CommandRunner, srcDir, outFile string, sizeBytes int64) error {
if sizeBytes < MinExt4Size {
return fmt.Errorf("ext4 size %d below minimum %d", sizeBytes, MinExt4Size)