support /var lvs in bootc

bootc-dev/bootc#2521
has new comments from Colin, let's prototype in the forge how implementing the --var and DPS support would look like.

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@jmarrero-bot open code can you summarize what the PR linked is trying to accomplish?

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@jmarrero-bot opencode can you summarize what the PR linked is trying to accomplish?

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@jmarrero opencode result for #2 (comment)

bootc PR #2521 aims to make separate /var filesystems—including LVM volumes and nested mounts such as /var/log—start with the content shipped in the container image.

Why it’s needed

Currently, bootc install to-filesystem seeds /var into bootc’s internal state directory. A separate filesystem mounted over /var or one of its subdirectories hides that content, leaving the actual volume empty.

What the draft implements

Detect filesystems already mounted under the installation target’s /var.
Populate empty mount trees from the image’s seeded /var, preserving metadata, applying SELinux labels, and syncing the filesystems.
Preserve any mount tree that already contains data, without merging into it.
Advertise an initialize-var-mounts capability through bootc container inspect, so image builders can detect support.
Extend tests for separate and nested volumes, and fix the test’s /boot UUID.

This applies to fresh to-filesystem installs; callers still arrange for those filesystems to mount at boot. It pairs with image-builder PR #2733.

Colin’s requested direction

Colin suggests changing the interface to:

Provide an explicit --var mount option.
Automatically discover and use a DPS (Discoverable Partitions Specification) “Variable Data Partition.”
Let --var= disable that automatic discovery and retain the default /var layout.
Report global capabilities through bootc --version.

Bottom line: the current draft fixes initialization of pre-mounted /var volumes; the proposed next step is for bootc to select and mount /var itself through explicit configuration or DPS discovery. Those review suggestions are not yet implemented in the draft.

_{bootc-bot · opencode · 25s · exit 0}

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@jmarrero-bot can you prototype how doing Colin's suggestions would look like?

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Status update (2026-10-13), replacing the earlier plan in this issue's body. The --var / DPS prototype in jmarrero-forge/bootc#1 predates the current direction and would need rework, so it's paused.

Problem. bootc install to-filesystem seeds the image's /var into the stateroot (libostree prepare_deployment_var() on OSTree, bootc's own copy on composefs). Filesystems mounted at the target's /var or below stay empty and hide that content at boot. Image builders that mount separate /var volumes hit this, and so do their post-install stages and the final relabel. Upstream issues: bootc-dev/bootc#1615, #997, #336.

Current PRs

install: Initialize separately mounted /var filesystems from the image bootc-dev/bootc#2521 (draft, 5f31d979): opt-in install to-filesystem --initialize-var-mounts. It discovers filesystems mounted under the target's /var, fills each empty tree from the seeded /var (nested mounts and hardlinks handled, SELinux labeled, syncfs), leaves non-empty trees whole, refuses symlinked mountpoints, and lists the feature in bootc --version. Remaining work: title and description, DCO sign-off, and replies to the review threads.
bootc: populate separate /var filesystems in bootc disk images osbuild/image-builder#2733 (draft, stale): it still detects support through container inspect, which #2521 no longer has. It needs updating to read bootc --version's Features: list.
osbuild: needs an initialize-var-mounts option on org.osbuild.bootc.install-to-filesystem. There's no upstream PR yet.

Proposed direction (to confirm on #2521). Defer the /var copy at install, then initialize the mounts from the image, so each file lands once:

install to-filesystem --defer-var (name TBD) skips seeding /var. On OSTree that needs a marker in the stateroot var now, or a libostree deploy option later.
--initialize-var-mounts copies from the image's /var into an assembled /var (the volumes bind-mounted over the stateroot var). Without --defer-var the result is the same as today.
A day-two command (e.g. bootc state initialize-var) runs the same routine on a booted system, for volumes added later.

Open decisions:

flag names (--defer-var vs --var=empty; keep --initialize-var-mounts?);
marker vs libostree option;
whether a re-run fills only empty volumes or missing files too;
who runs the second step after a deferred install;
PR structure (keep #2521 minimal, then follow-ups).

Testing still missing for #2521 revision 2, tracked in a sub-issue: a composefs install and boot, upgrade and rollback with separate /var volumes, multiple VGs, nested-mount edge cases, and the image-builder end-to-end path, all with synthetic layouts.

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support /var lvs in bootc #2

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support /var lvs in bootc #2

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jmarrero commented on Oct 2, 2026

jmarrero commented on Oct 2, 2026

jmarrero-bot commented on Oct 2, 2026

jmarrero-bot commented on Oct 2, 2026

Why it’s needed

What the draft implements

Colin’s requested direction

jmarrero commented on Oct 2, 2026

jmarrero-bot commented on Oct 2, 2026

jmarrero-bot commented on Oct 13, 2026

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