feat: support multiple MirageOS block devices

[pocopepe]

Description

Block devices from #315, comma separated as discussed.

solo5BlkDev, block and blkMntPoint now take ordered comma separated lists, mapped positionally. Single device setups are unaffected. Added guards for empty list entries and for mixing a / mounted block with others, both error out instead of silently mismapping.

3.1 of 3 from #315.

Related issues

• Related: Support multiple block and network devices over Solo5/MirageOS #315

How was this tested?

go test ./pkg/unikontainers/... -v -run "TestHandleExplicitBlockImages|TestNoRootfsMultipleBlockDevs|TestMirageMultipleBlkDevs"

=== RUN   TestHandleExplicitBlockImages
=== RUN   TestHandleExplicitBlockImages/parses_an_ordered_list_of_block_images_and_mount_points
=== RUN   TestHandleExplicitBlockImages/single_image_stays_backward_compatible
=== RUN   TestHandleExplicitBlockImages/empty_block_image_yields_no_devices
=== RUN   TestHandleExplicitBlockImages/mismatched_counts_return_an_error
=== RUN   TestHandleExplicitBlockImages/rootfs_combined_with_other_block_devices_returns_an_error
=== RUN   TestHandleExplicitBlockImages/empty_entries_return_an_error
--- PASS: TestHandleExplicitBlockImages (0.00s)
=== RUN   TestNoRootfsMultipleBlockDevs
--- PASS: TestNoRootfsMultipleBlockDevs (0.00s)
PASS
ok      github.com/urunc-dev/urunc/pkg/unikontainers    0.010s
=== RUN   TestMirageMultipleBlkDevs
--- PASS: TestMirageMultipleBlkDevs (0.00s)
PASS
ok      github.com/urunc-dev/urunc/pkg/unikontainers/unikernels (cached)

Built a MirageOS unikernel declaring two block devices in its Solo5 manifest, storage and data, and ran it through urunc/containerd end to end.

Both devices declared and attached:

$ sudo nerdctl run --rm --runtime io.containerd.urunc.v2 --snapshotter devmapper --network=none docker.io/pocopepe/mirage-multiblock:multi
Solo5: Bindings version v0.12.0
...
2026-08-05T20:14:49-00:00: [INFO] [application] multiblock: block 'storage' -> 20480 sectors of 512 bytes
2026-08-05T20:14:49-00:00: [INFO] [application] multiblock: block 'data'    -> 10240 sectors of 512 bytes
2026-08-05T20:14:49-00:00: [INFO] [application] multiblock: both block devices attached successfully
Solo5: solo5_exit(0) called

Mismatched annotation counts, caught before the VM ever boots:

$ sudo nerdctl run --rm --runtime io.containerd.urunc.v2 --snapshotter devmapper --network=none docker.io/pocopepe/mirage-multiblock:mismatch
FATA[0000] failed to create shim task: OCI runtime create failed: failed to get block devices to attach in sandbox: block images (2) and mount points (1) must have the same count

Pushed images:

• docker.io/pocopepe/mirage-multiblock:multi
• docker.io/pocopepe/mirage-multiblock:mismatch

LLM usage

Claude Sonnet 5

Checklist

• I have read the contribution guide.
• The linter passes locally (make lint).
• The e2e tests of at least one tool pass locally (make test_ctr, make test_nerdctl, make test_docker, make test_crictl).
• If LLMs were used: I have read the llm policy.

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