stages: fix btrfs subvolume creation under subdirectories

The code currently does not support btrfs subvolumes that are not
directly under the root directory. This commit fixes this by adding
`-p` to `btrfs subvolume create` and adding an integration test.

Closes: https://github.com/osbuild/osbuild/issues/1882

stages/org.osbuild.btrfs.subvol

@@ -13,7 +13,7 @@ def main(paths, options):
         name = vol["name"].lstrip("/")
         subvol = os.path.join(volume, name)
 
-        cmd = ["btrfs", "subvolume", "create", subvol]
+        cmd = ["btrfs", "subvolume", "create", "-p", subvol]
         subprocess.run(cmd, encoding='utf-8', check=True)
 
 

stages/test/test_btrfs_subvol.py

@@ -0,0 +1,46 @@
+#!/usr/bin/python3
+
+import contextlib
+import os
+import subprocess
+
+import pytest
+
+from osbuild.testutil import has_executable
+
+STAGE_NAME = "org.osbuild.btrfs.subvol"
+
+
+def make_btrfs_disk(tmp_path):
+    fake_disk_path = tmp_path / "fake.img"
+    with fake_disk_path.open("w") as fp:
+        fp.truncate(110 * 1024 * 1024)
+    subprocess.run(["mkfs.btrfs", fake_disk_path], check=True)
+    return fake_disk_path
+
+
+@pytest.mark.skipif(os.getuid() != 0, reason="needs root")
+@pytest.mark.skipif(not has_executable("mkfs.btrfs"), reason="need mkfs.btrfs")
+def test_btrfs_subvol_integration(tmp_path, stage_module):
+    fake_disk_path = make_btrfs_disk(tmp_path)
+    fake_disk_mnt = tmp_path / "mnt"
+    fake_disk_mnt.mkdir()
+    with contextlib.ExitStack() as cm:
+        subprocess.run(["mount", fake_disk_path, fake_disk_mnt], check=True)
+        cm.callback(subprocess.run, ["umount", fake_disk_mnt], check=True)
+
+        paths = {
+            "mounts": fake_disk_mnt,
+        }
+        options = {
+            "subvolumes": [
+                {"name": "/asubvol"},
+                {"name": "/subvols/root"},
+            ],
+        }
+        stage_module.main(paths, options)
+
+        output = subprocess.check_output([
+            "btrfs", "subvolume", "list", fake_disk_mnt], encoding="utf-8")
+        assert "path asubvol\n" in output
+        assert "path subvols/root\n" in output