tests: check for relabeling rather than overlay

Instead of checking for overlayfs, let's explicitly check for our
ability to relabel files since we now have a `libtest` function to do
this. Also port that logic to `libostreetest`.

Note that overlayfs *does* allow manipulating user xattrs. So ideally,
we should break down `OSTREE_NO_XATTRS` further to distinguish between
tests that use bare repos from other modes.

We check the current directory instead of `/` so that developers can
just point `TEST_TMPDIR` to a non-overlayfs mount point when hacking
from a container.

Closes: #1170
Approved by: cgwalters

1 files changed, 75 insertions, 16 deletions

diff --git a/tests/libostreetest.c b/tests/libostreetest.c
index 6186a73a..496ff740 100644
--- a/tests/libostreetest.c
+++ b/tests/libostreetest.c
@@ -72,6 +72,68 @@ ot_test_setup_repo (GCancellable *cancellable,
   return g_steal_pointer (&ret_repo);
 }
 
+/* Determine whether we're able to relabel files. Needed for bare tests. */
+gboolean
+ot_check_relabeling (gboolean *can_relabel,
+                     GError  **error)
+{
+  g_auto(GLnxTmpfile) tmpf = { 0, };
+  if (!glnx_open_tmpfile_linkable_at (AT_FDCWD, ".", O_RDWR | O_CLOEXEC, &tmpf, error))
+    return FALSE;
+
+  g_autoptr(GError) local_error = NULL;
+  g_autoptr(GBytes) bytes = glnx_fgetxattr_bytes (tmpf.fd, "security.selinux", &local_error);
+  if (!bytes)
+    {
+      /* libglnx preserves errno */
+      if (G_IN_SET (errno, ENOTSUP, ENODATA))
+        {
+          *can_relabel = FALSE;
+          return TRUE;
+        }
+      g_propagate_error (error, g_steal_pointer (&local_error));
+      return FALSE;
+    }
+
+  gsize data_len;
+  const guint8 *data = g_bytes_get_data (bytes, &data_len);
+  if (fsetxattr (tmpf.fd, "security.selinux", data, data_len, 0) < 0)
+    {
+      if (errno == ENOTSUP)
+        {
+          *can_relabel = FALSE;
+          return TRUE;
+        }
+      return glnx_throw_errno_prefix (error, "fsetxattr");
+    }
+
+  *can_relabel = TRUE;
+  return TRUE;
+}
+
+/* Determine whether the filesystem supports getting/setting user xattrs. */
+gboolean
+ot_check_user_xattrs (gboolean *has_user_xattrs,
+                      GError  **error)
+{
+  g_auto(GLnxTmpfile) tmpf = { 0, };
+  if (!glnx_open_tmpfile_linkable_at (AT_FDCWD, ".", O_RDWR | O_CLOEXEC, &tmpf, error))
+    return FALSE;
+
+  if (fsetxattr (tmpf.fd, "user.test", "novalue", strlen ("novalue"), 0) < 0)
+    {
+      if (errno == ENOTSUP)
+        {
+          *has_user_xattrs = FALSE;
+          return TRUE;
+        }
+      return glnx_throw_errno_prefix (error, "fsetxattr");
+    }
+
+  *has_user_xattrs = TRUE;
+  return TRUE;
+}
+
 OstreeSysroot *
 ot_test_setup_sysroot (GCancellable *cancellable,
                        GError **error)
@@ -79,22 +141,19 @@ ot_test_setup_sysroot (GCancellable *cancellable,
   if (!ot_test_run_libtest ("setup_os_repository \"archive\" \"syslinux\"", error))
     return FALSE;
 
-  struct statfs stbuf;
-  { g_autoptr(GString) buf = g_string_new ("mutable-deployments");
-    if (statfs ("/", &stbuf) < 0)
-      return glnx_null_throw_errno (error);
-    /* Keep this in sync with the overlayfs bits in libtest.sh */
-#ifndef OVERLAYFS_SUPER_MAGIC
-#define OVERLAYFS_SUPER_MAGIC 0x794c7630
-#endif
-    if (stbuf.f_type == OVERLAYFS_SUPER_MAGIC)
-      {
-        g_print ("libostreetest: detected overlayfs\n");
-        g_string_append (buf, ",no-xattrs");
-      }
-    /* Make sure deployments are mutable */
-    g_setenv ("OSTREE_SYSROOT_DEBUG", buf->str, TRUE);
-  }
+  g_autoptr(GString) buf = g_string_new ("mutable-deployments");
+
+  gboolean can_relabel;
+  if (!ot_check_relabeling (&can_relabel, error))
+    return FALSE;
+  if (!can_relabel)
+    {
+      g_print ("libostreetest: can't relabel, turning off xattrs\n");
+      g_string_append (buf, ",no-xattrs");
+    }
+
+  /* Make sure deployments are mutable */
+  g_setenv ("OSTREE_SYSROOT_DEBUG", buf->str, TRUE);
 
   g_autoptr(GFile) sysroot_path = g_file_new_for_path ("sysroot");
   return ostree_sysroot_new (sysroot_path);