Feat: Introduce Transparent LVM Support for azure-chroot Builder by MrCaedes · Pull Request #583 · hashicorp/packer-plugin-azure

MrCaedes · 2026-02-24T11:17:09Z

Description

Adds simplified built-in LVM support to the azure-chroot builder.

Multiple Azure Marketplace images (i.e., RHEL 8/9/10, Oracle Linux, etc) ship with LVM-based disk layouts. Previously, the azure-chroot builder only supported mounting raw partitions - making these images unusable without manual workarounds which are squirreled away in Enterprise Wikis.

This PR adds transparent LVM detection and activation so that LVM-based source disks "just work" - testing based on RHEL 8 / 9 / 10, and follows on from the changes made as part of #582. Fist bump to VRay27 for their continued support in testing 🙌

What changed:

step_setup_lvm.go: New build step; leverages partprobe and udevadm settle for device discovery, alongside pvscan and vgchange.
step_pre_unmount_commands.go: Facilitate users in running commands on the host after provisioning but before unmount (e.g., fstrim, sync, etc - traditionally done using a shell script step)
step_early_cleanup.go: handles teardown for LVM; built-in cleanup isn't LVM-aware.
builder.go: addition of lvm_root_device to override auto-detection with explicit device paths (w/ validation), pre_unmount_commands for on-host commands to run before unmount.

Updated required documentation; regenerated hcl2spec via go generate - and webdocs using make.

Rollback Plan

If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

No changes to security controls; LVM step(s) execute standard Linux storage utilities on the host VM. No new changes introduced beyond this.

Copilot

Pull request overview

Adds transparent LVM handling to the azure-chroot builder so LVM-based source disks can be mounted automatically, plus a new hook to run host-side commands just before unmount/teardown.

Changes:

Introduces a new StepSetupLVM step that detects/activates VGs and selects a root LV, with cleanup to deactivate VGs.
Adds pre_unmount_commands support via a new build step executed after provisioning and before unmount.
Extends builder config/docs (lvm_root_device, pre_unmount_commands) and replaces SDK early-cleanup with an LVM-aware version.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
docs/builders/chroot.mdx	Documents new LVM behavior, options, and examples.
docs-partials/builder/azure/chroot/Config-not-required.mdx	Adds config reference entries for `lvm_root_device` and `pre_unmount_commands`.
builder/azure/chroot/step_setup_lvm.go	Implements LVM discovery, activation, root LV selection, and VG deactivation cleanup.
builder/azure/chroot/step_setup_lvm_other.go	Provides no-op step stub for unsupported OS build tags.
builder/azure/chroot/step_setup_lvm_test.go	Verifies step presence/order and config passthrough for new steps.
builder/azure/chroot/step_pre_unmount_commands.go	Runs host-side commands before unmount/LVM deactivation.
builder/azure/chroot/step_mount_device.go	Adjusts mount device computation when LVM is active.
builder/azure/chroot/step_early_cleanup.go	Adds custom early cleanup ordering to include LVM deactivation.
builder/azure/chroot/builder.go	Adds config fields, validation, and wires new steps into the chain.
builder/azure/chroot/builder.hcl2spec.go	Regenerates HCL2 spec to include new fields.
.web-docs/components/builder/chroot/README.md	Regenerated web docs reflecting new LVM support and options.

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Copilot · 2026-02-25T11:54:48Z

+`vgscan`, `vgchange`, `lvs`) to be installed on the host VM. The `partprobe`
+and `udevadm` utilities are also used for device discovery.


The docs list lvm2 utilities required for LVM support but omits a few commands used by the implementation (e.g., pvs, lvchange, vgmknodes; plus blkid/dmsetup are used for swap detection/diagnostics). Either update the note to include these dependencies or clarify which ones are strictly required vs. best-effort diagnostics.

Suggested change

`vgscan`, `vgchange`, `lvs`) to be installed on the host VM. The `partprobe`

and `udevadm` utilities are also used for device discovery.

`pvs`, `vgscan`, `vgchange`, `lvchange`, `lvs`, `vgmknodes`) to be installed on

the host VM. The `partprobe` and `udevadm` utilities are also used for device

discovery, and `blkid`/`dmsetup` are used for best-effort swap detection and

diagnostics (the builder can run without them, but with reduced introspection).

Copilot · 2026-02-25T11:54:48Z

+func Test_buildsteps_LVM(t *testing.T) {
+	info := &client.ComputeInfo{
+		Location:          "northpole",
+		Name:              "unittestVM",
+		ResourceGroupName: "unittestResourceGroup",


These tests validate step ordering/config passthrough, but they don’t cover the new LV-selection heuristics in step_setup_lvm.go (attr filtering, swap exclusion via blkid, name matching, /dev/mapper parsing, etc.). Consider adding unit tests for the pure helper functions and/or refactoring command output parsing so findRootLV can be tested deterministically.

MrCaedes · 2026-02-26T01:52:48Z

I've accepted the changes raised by CoPilot, from its additions in this thread; tests around LVM have been added, with cases expanded using AI - for broader logic coverage.

tanmay-hc · 2026-02-25T12:53:54Z

+
+func (s *StepSetupLVM) CleanupFunc(state multistep.StateBag) error {
+	return nil
+}


Can you explain what's this "other" file?

step_setup_lvm_other.go acts as a non-functional stub file, ensuring that it can be compiled on multiple platforms. Without this stub file, attempting to compile this on Windows or Mac will result in a compilation error - as it'll be expecting a "StepSetupLVM" (which wouldn't be provided without this).

tanmay-hc · 2026-02-25T12:56:02Z

+	return multistep.ActionContinue
+}
+
+func (s *StepPreUnmountCommands) Cleanup(state multistep.StateBag) {}


Consider adding some tests for this step

tanmay-hc · 2026-03-17T06:03:58Z

@MrCaedes Please rebase the branch. Changes looks good to me.

- Introduced LVMRootDevice configuration option to specify the root device path for LVM. - Added PreUnmountCommands to execute commands before unmounting the chroot. - Implemented StepSetupLVM to detect and activate LVM volume groups on attached disks. - Created StepPreUnmountCommands to run user-defined commands prior to unmounting. - Developed custom StepEarlyCleanup to handle LVM deactivation during cleanup. - Updated documentation to include LVM support details and usage examples. - Added tests to verify LVM integration and step order in the build process.

…osssubscription-acg

…sting

…nput

Removing redundant message (i.e., originally outputted unconditionally)

Removes hardcoded values in favour of a const, in line with other filles; moves other timouts. UdevSettle passed as CLI (hence string)

Respect context cancellation; remove blind loops. Retain `attempt` as gate for retry loop and for logging purposes.

Switch to "slices.Contains" for improved readability; negligible performance improvement.

MrCaedes requested a review from a team as a code owner February 24, 2026 11:17

tanmay-hc requested a review from Copilot February 25, 2026 11:48

Copilot started reviewing on behalf of tanmay-hc February 25, 2026 11:48 View session

Copilot AI reviewed Feb 25, 2026

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tanmay-hc reviewed Feb 25, 2026

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Comment thread builder/azure/chroot/step_setup_lvm.go

tanmay-hc reviewed Feb 25, 2026

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Comment thread builder/azure/chroot/step_setup_lvm.go

tanmay-hc requested changes Mar 2, 2026

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atombrella reviewed Mar 11, 2026

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Comment thread builder/azure/chroot/builder.go Outdated

atombrella reviewed Mar 11, 2026

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Comment thread builder/azure/chroot/step_setup_lvm_test.go

MrCaedes added 12 commits March 22, 2026 20:27

chore: regenerate HCL2 spec and docs after cherry-pick from chroot-cr…

f15b9a1

…osssubscription-acg

chore: documentation accuracy and regeneration as part of .CONTRIBUTING

8071264

fix: use device path directly to support FreeBSD

c6603f0

fix: resolve error propagation and extract helpers to support unit te…

9f97ff3

…sting

fix: resolve path traversal and potential injection - validate user i…

2f61c61

…nput

feat: add unit tests for coverage of lvm behaviour (ai expanded)

a0ffd92

chore: resolve gofmt and linting for contribution

7bbd226

res: 583#discussion_r2852714789

01673c9

Removing redundant message (i.e., originally outputted unconditionally)

res: 583#discussion_r2852719535

252fd9c

Removes hardcoded values in favour of a const, in line with other filles; moves other timouts. UdevSettle passed as CLI (hence string)

res: 583#discussion_r2852691547

18a8451

Respect context cancellation; remove blind loops. Retain `attempt` as gate for retry loop and for logging purposes.

res: 583#discussion_r2916262149

35ed8d5

Switch to "slices.Contains" for improved readability; negligible performance improvement.

MrCaedes force-pushed the lvm branch from db670d9 to 35ed8d5 Compare March 22, 2026 20:29

MrCaedes added 2 commits March 22, 2026 20:45

Resolve linting errors raised from golanci-lint v2 upgrades

cd5cb83

Resolve remaining lint errors from golanci-lint v2

ed556e7

tanmay-hc approved these changes Mar 23, 2026

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tanmay-hc merged commit 1a8e5f5 into hashicorp:main Mar 23, 2026
12 checks passed

lemeurherve mentioned this pull request Mar 27, 2026

Bump packer azure plugin version to 2.6.0 jenkins-infra/packer-images#2591

Merged

		`vgscan`, `vgchange`, `lvs`) to be installed on the host VM. The `partprobe`
		and `udevadm` utilities are also used for device discovery.

-`vgscan`, `vgchange`, `lvs`) to be installed on the host VM. The `partprobe`
-and `udevadm` utilities are also used for device discovery.
+`pvs`, `vgscan`, `vgchange`, `lvchange`, `lvs`, `vgmknodes`) to be installed on
+the host VM. The `partprobe` and `udevadm` utilities are also used for device
+discovery, and `blkid`/`dmsetup` are used for best-effort swap detection and
+diagnostics (the builder can run without them, but with reduced introspection).

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MrCaedes commented Feb 24, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Description

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MrCaedes commented Feb 26, 2026

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MrCaedes commented Feb 24, 2026 •

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