repart: make COW behavior configurable

systemd-repart currently forces newly created image files into NOCOW mode. That prevents files from being reflinked into the image, making image builds slower and increasing their disk usage on filesystems that support cloning. Add a tristate --cow= option. By default, leave the filesystem or parent directory COW policy unchanged. With --cow=yes, explicitly enable COW; with --cow=no, retain the previous behavior of forcing NOCOW. Add XO_COW as the counterpart to XO_NOCOW so xopenat_full() applies either policy while retaining its normal creation-error cleanup. Document the new option and extend TEST-58-REPART to verify inherited COW and NOCOW policies as well as explicit COW and NOCOW overrides. Compare the unset behavior with the filesystem default so the test also works on nodatacow mounts, and skip it when the inode attribute is unsupported. Signed-off-by: Daan De Meyer <daan@amutable.com>
2026-07-15 09:22:58 +02:00
parent d153b49473
commit 28b1e4ea16
5 changed files with 140 additions and 10 deletions
@@ -94,6 +94,108 @@ else
    exit 1
 fi

+testcase_cow() {
+    local attrs cow_image default_nocow defs image imgs nocow_image probe
+
+    defs="$(mktemp --directory "/tmp/test-repart.defs.XXXXXXXXXX")"
+    imgs="$(mktemp --directory "/var/tmp/test-repart.imgs.XXXXXXXXXX")"
+    # shellcheck disable=SC2064
+    trap "rm -rf '$defs' '$imgs'" RETURN
+
+    # Skip the checks entirely if the underlying filesystem does not support the attribute.
+    if ! chattr -C "$imgs"; then
+        echo "NOCOW is not supported on $imgs, skipping tests"
+        return
+    fi
+
+    probe="$imgs/probe"
+    touch "$probe"
+    if ! chattr +C "$probe"; then
+        echo "NOCOW is not supported on $imgs, skipping tests"
+        return
+    fi
+    if ! chattr -C "$probe"; then
+        echo "COW is not supported on $imgs, skipping tests"
+        return
+    fi
+    rm "$probe"
+
+    chattr +C "$imgs"
+
+    image="$imgs/inherit-nocow.raw"
+    systemd-repart --offline="$OFFLINE" \
+                   --definitions="$defs" \
+                   --empty=create \
+                   --size=16M \
+                   --cow=auto \
+                   --dry-run=no \
+                   "$image"
+
+    attrs="$(lsattr -d -- "$image")"
+    assert_neq "$attrs" ""
+    read -r attrs _ <<<"$attrs"
+    assert_in "C" "$attrs"
+
+    cow_image="$imgs/cow.raw"
+    systemd-repart --offline="$OFFLINE" \
+                   --definitions="$defs" \
+                   --empty=create \
+                   --size=16M \
+                   --cow=yes \
+                   --dry-run=no \
+                   "$cow_image"
+
+    attrs="$(lsattr -d -- "$cow_image")"
+    assert_neq "$attrs" ""
+    read -r attrs _ <<<"$attrs"
+    assert_not_in "C" "$attrs"
+
+    chattr -C "$imgs"
+
+    probe="$imgs/probe"
+    touch "$probe"
+    attrs="$(lsattr -d -- "$probe")"
+    assert_neq "$attrs" ""
+    read -r attrs _ <<<"$attrs"
+    if [[ "$attrs" == *C* ]]; then
+        default_nocow=1
+    else
+        default_nocow=0
+    fi
+    rm "$probe"
+
+    image="$imgs/inherit-cow.raw"
+    systemd-repart --offline="$OFFLINE" \
+                   --definitions="$defs" \
+                   --empty=create \
+                   --size=16M \
+                   --dry-run=no \
+                   "$image"
+
+    attrs="$(lsattr -d -- "$image")"
+    assert_neq "$attrs" ""
+    read -r attrs _ <<<"$attrs"
+    if (( default_nocow )); then
+        assert_in "C" "$attrs"
+    else
+        assert_not_in "C" "$attrs"
+    fi
+
+    nocow_image="$imgs/nocow.raw"
+    systemd-repart --offline="$OFFLINE" \
+                   --definitions="$defs" \
+                   --empty=create \
+                   --size=16M \
+                   --cow=no \
+                   --dry-run=no \
+                   "$nocow_image"
+
+    attrs="$(lsattr -d -- "$nocow_image")"
+    assert_neq "$attrs" ""
+    read -r attrs _ <<<"$attrs"
+    assert_in "C" "$attrs"
+}
+
 testcase_basic() {
    local defs imgs output
    local loop volume