test/run: add devices test for loopback devices

Add a new devices run time test and add basic checks for the
org.osbuild.loopback device.

test/run/test_devices.py

@@ -0,0 +1,80 @@
+#!/usr/bin/python3
+
+#
+# Runtime Tests for Device Host Services
+#
+
+import os
+import tempfile
+
+import pytest
+
+from osbuild import devices, host, loop, meta
+
+from ..test import TestBase
+
+
+@pytest.fixture(name="tmpdir")
+def tmpdir_fixture():
+    with tempfile.TemporaryDirectory(prefix="test-devices-") as tmp:
+        yield tmp
+
+
+@pytest.mark.skipif(not TestBase.can_bind_mount(), reason="root only")
+def test_loopback_basic(tmpdir):
+    index = meta.Index(os.curdir)
+    info = index.get_module_info("Device", "org.osbuild.loopback")
+
+    tree = os.path.join(tmpdir, "tree")
+    os.makedirs(tree)
+
+    devpath = os.path.join(tmpdir, "dev")
+    os.makedirs(devpath)
+
+    size = 1024 * 1024
+    filename = os.path.join(tree, "image.img")
+    with open(filename, "wb") as f:
+        f.truncate(size)
+        sb = os.fstat(f.fileno())
+
+    testfile = os.path.join(tmpdir, "test.img")
+
+    options = {
+        "filename": "image.img",
+        "start": 0,
+        "size": size // 512  # size is in sectors / blocks
+    }
+
+    dev = devices.Device("loop", info, options)
+
+    with host.ServiceManager() as mgr:
+        reply = dev.open(mgr, devpath, tree)
+        assert reply
+        assert reply["path"]
+
+        node = reply["path"]
+        assert os.path.exists(os.path.join(devpath, node))
+
+        minor = reply["node"]["minor"]
+        lo = loop.Loop(minor)
+        li = lo.get_status()
+
+        assert li.lo_offset == 0
+        assert li.lo_sizelimit == size
+        assert li.lo_inode == sb.st_ino
+
+        with pytest.raises(OSError):
+            with open(testfile, "wb") as f:
+                f.truncate(1)
+                lo.set_fd(f.fileno())
+
+        lo.close()
+
+        uid = f"device/{dev.name}"
+        client = mgr.services[uid]
+
+        client.call("close", None)
+
+        lo = loop.Loop(minor)
+        with open(filename, "r") as f:
+            assert not lo.is_bound_to(f.fileno())