Add support for larger number of larger using GPT#181
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Pull request overview
Adds a new strategy for handling many EROFS layer mounts by packing plain (single-device) EROFS mounts into a single GPT-partitioned VMDK, reducing virtio-blk device consumption while preserving existing behavior for multi-device EROFS mounts.
Changes:
- Defer and batch plain EROFS mounts in the shim; above a threshold, generate/attach one GPT VMDK and mount partitions (e.g.,
/dev/vda1,/dev/vda2, …). - Introduce GPT layout generation (header/tail blobs, partition table) and a GPT-aware VMDK descriptor writer that can use ZERO extents (or a padding-file fallback).
- Add unit tests covering GPT layout/descriptor generation and mount transformation behavior; patch libkrun build to use a locally patched
imagocrate for VMDK extent-boundary correctness.
Reviewed changes
Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.
Show a summary per file
| File | Description |
|---|---|
| internal/shim/task/mount.go | Defers plain EROFS mounts and conditionally packs them into a GPT-partitioned VMDK; keeps multi-device EROFS behavior inline. |
| internal/shim/task/mount_test.go | Adds coverage for plain vs multi-device EROFS and GPT packing threshold behavior. |
| internal/erofs/vmdk.go | Adds GPT VMDK descriptor emission (ZERO extents / padding fallback) and helper blob/pad writers. |
| internal/erofs/gpt.go | Implements deterministic GPT layout computation and header/tail blob writers for partitioned layer disks. |
| internal/erofs/gpt_test.go | Tests GPT layout correctness, determinism, CRCs, and header/tail structure. |
| internal/erofs/vmdk_gpt_test.go | Tests GPT VMDK descriptor extent ordering and the to-file writer (aux file generation). |
| internal/erofs/no_copy_check_test.go | Adds an informational “no data copy” test that currently runs as a normal unit test. |
| Dockerfile | Patches imago in the libkrun build stage to fix extent-boundary reads for GPT VMDKs. |
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| if len(disk) > 36 { | ||
| disk = disk[:36] | ||
| } | ||
| mergedfsPath := filepath.Join(bundleDir, "merged_fs.vmdk") |
hsiangkao
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| // Write the GPT VMDK and its auxiliary blobs into bundleDir so the | ||
| // shim does not mutate the source image directories. Cache by | ||
| // stat-check: setupMounts may be called more than once per bundle | ||
| // (e.g. on restore) but the layer set for a given bundle is fixed. | ||
| gptPath := filepath.Join(bundleDir, "merged_fs_gpt.vmdk") | ||
| if _, err := os.Stat(gptPath); err != nil { | ||
| if !os.IsNotExist(err) { | ||
| log.G(ctx).Warnf("failed to stat %v: %v", gptPath, err) | ||
| return fmt.Errorf("erofs gpt vmdk: %w", errdefs.ErrNotImplemented) | ||
| } | ||
| if err := erofs.DumpGPTVMDKDescriptorToFile(gptPath, 0xfffffffe, sources); err != nil { | ||
| log.G(ctx).Warnf("failed to generate %v: %v", gptPath, err) | ||
| return fmt.Errorf("erofs gpt vmdk: %w", errdefs.ErrNotImplemented) | ||
| } | ||
| } |
Signed-off-by: Derek McGowan <derek@mcg.dev>
Use gpt to layout erofs partitions into a single vmdk device to attach all erofs devices in a single block device. Signed-off-by: Derek McGowan <derek@mcg.dev>
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Use gpt to layout erofs partitions into a single vmdk device to attach
all erofs devices in a single block device.