[cdalar]

Summary

Adds onctl create --rootfs-size <MiB> (fc.rootfsSizeMib) for Firecracker: after a microVM's rootfs is copied from the base image, it's grown to that size, file and ext4 filesystem both. Default 0 keeps today's behavior.

Motivation: boxctl.io boxes all get the base image's 4 GiB disk regardless of size, so e.g. a Rancher install on a large (4 vCPU / 16 GiB) box dies on kubelet DiskPressure. With this, boxctl-vms can give each size its own disk from one small base image (companion: cdalar/boxctl-vms#108, which keeps pause/export diffs from shipping the grown tail's zeros).

Technical details

• DebugfsRootfsPreparer.GrowRootfs: sparse truncate → e2fsck -f -y (exit 1/2 = corrected, still usable; ≥4 fails) → offline resize2fs. Costs no host disk until the guest writes; reflinked base blocks stay shared. Refuses to shrink below the base image; same size is a no-op.
• New optional cloud.RootfsResizer interface, mirroring BaseImageIdentifier — but not best-effort: Deploy fails and cleans up the VM dir when a size is set and the preparer can't honor it, rather than booting a smaller disk than asked for.
• Firecracker only. Cloud Hypervisor is untouched (boxctl.io only uses it for fixed-size Windows boxes).

Testing

• New unit tests: grow call order and resulting size, no-op, shrink refusal (file untouched), e2fsck exit-code handling, resize2fs failure, and Deploy wiring (grows with the right path/size, default doesn't, failure cleans up, missing resizer fails).
• TestDebugfsRootfsPreparer_GrowRootfs_RealExt4 runs real e2fsprogs on a real ext4 image and checks the filesystem's block count and a clean fsck. Skipped locally (macOS, no e2fsprogs) — should run on the Linux CI runner.
• go test ./... passes with a clean HOME; go vet, gofmt, make clean. (With a real ~/.onctl present, TestReadConfig_NoConfigDirectory and TestCreateFlagsBindToViper fail on main too — they read the home config.)

🤖 Generated with Claude Code

https://claude.ai/code/session_01Ngxnc2n5dZEkDj6cR8KhNN

[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 36.85%. Comparing base (ea19670) to head (723be1a).

Files with missing lines	Patch %	Lines
internal/providerfc/common.go	93.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1150      +/-   ##
==========================================
+ Coverage   36.58%   36.85%   +0.27%     
==========================================
  Files          51       51              
  Lines        5615     5643      +28     
==========================================
+ Hits         2054     2080      +26     
- Misses       3561     3563       +2     

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