storage: ID-map hardlink reconstruction changes directory mtimes

[bbartels]

Problem

Creating a mapped container from an image changes the modification times of
directories containing hardlinks to the current time. The archived timestamps
are correct. Integer-second timestamps reproduce the problem, so this is not
fractional timestamp rounding.

Reproduction

Use the script below on a disposable rootful Podman host. It imports
a scratch filesystem with hardlinks in two directories and fixed mtimes, then
creates a container with --uidmap 0:1:65535 --gidmap 0:1:65535 and inspects it
through podman mount. No container execution or image download is required.

Expected: both directory mtimes remain 1700000000; hardlinks and contents
remain intact.

Actual: directory mtimes change during materialization, while hardlinks and
contents remain intact.

#!/usr/bin/env bash
set -euo pipefail

# Run as root on a disposable Linux Podman host. No image pull or execution.
test "$(id -u)" -eq 0
engine="${PODMAN:-podman}"
work="$(mktemp -d)"
name="directory-mtime-$(basename "$work")"
name="${name,,}"
image="localhost/$name:test"
cleanup() {
    "$engine" rm -f "$name" >/dev/null 2>&1 || true
    "$engine" rmi "$image" >/dev/null 2>&1 || true
    rm -rf "$work"
}
trap cleanup EXIT
mkdir -p "$work/tree/a" "$work/tree/b"
printf 'contents\n' > "$work/tree/a/one"
ln "$work/tree/a/one" "$work/tree/a/two"
ln "$work/tree/a/one" "$work/tree/b/one"
ln "$work/tree/a/one" "$work/tree/b/two"
touch -d @1700000000 "$work/tree/a/one" "$work/tree/a" "$work/tree/b" "$work/tree"
tar --format=pax --numeric-owner --owner=0 --group=0 -C "$work/tree" -cf "$work/rootfs.tar" .
"$engine" import "$work/rootfs.tar" "$image"
"$engine" create --name "$name" --network=none --pull=never \
    --uidmap 0:1:65535 --gidmap 0:1:65535 "$image" /unused
root="$("$engine" mount "$name")"
stat -c '%n mtime=%Y owner=%u:%g inode=%i links=%h' "$root/a" "$root/b" "$root/a/one" "$root/b/two"
test "$(stat -c %i "$root/a/one")" = "$(stat -c %i "$root/b/two")"
test "$(cat "$root/a/one")" = contents
test "$(stat -c %Y "$root/a")" = 1700000000
test "$(stat -c %Y "$root/b")" = 1700000000
echo 'Directory mtimes preserved'

Diagnosis

storage/drivers/chown_unix.go reconstructs duplicate hardlinks by removing and
recreating their entries. Those operations change the destination directory's
mtime. This also happens for unchanged IDs. A direct filesystem regression
reproduces the same defect without archive extraction.

Version and evidence

• Source assessed: container-libs 49fe7190f3ecd16fe4dcfd9e749ae480d4021a6c.
• Consumer context: Podman 6.1.1, storage 1.64.0, rootful native overlay on XFS.
• Direct root regression: five tests fail on the base implementation and pass
  for 25 race-enabled repetitions with the patch, without skips.
• Minimal Podman reproducer: exits 1 before and 0 after the candidate.
• A broader probe also observes /a retaining host owner 0:0 in both stock
  and candidate. That separate ownership assertion remains failing; the positive
  engine result here is specifically directory-mtime preservation.
• Attach the final relevant results from verification.md and add your own
  sanitized podman version / podman info --debug output.