tests: virtio-9p: ".." cannot be used to walk out of the shared directory

According to the 9P spec at http://man.cat-v.org/plan_9/5/intro, the
parent directory of the root directory of a server's tree is itself.
This test hence checks that the qid of the root directory as returned by
attach is the same as the qid of ".." when walking from the root directory.
Signed-off-by: NGreg Kurz <groug@kaod.org>

tests/virtio-9p-test.c

@@ -450,6 +450,25 @@ static void fs_walk_no_slash(QVirtIO9P *v9p)
     g_free(wnames[0]);
 }
 
+static void fs_walk_dotdot(QVirtIO9P *v9p)
+{
+    char *const wnames[] = { g_strdup("..") };
+    v9fs_qid root_qid, *wqid;
+    P9Req *req;
+
+    fs_version(v9p);
+    req = v9fs_tattach(v9p, 0, getuid());
+    v9fs_rattach(req, &root_qid);
+
+    req = v9fs_twalk(v9p, 0, 1, 1, wnames);
+    v9fs_rwalk(req, NULL, &wqid); /* We now we'll get one qid */
+
+    g_assert_cmpmem(&root_qid, 13, wqid[0], 13);
+
+    g_free(wqid);
+    g_free(wnames[0]);
+}
+
 typedef void (*v9fs_test_fn)(QVirtIO9P *v9p);
 
 static void v9fs_run_pci_test(gconstpointer data)
@@ -477,6 +496,8 @@ int main(int argc, char **argv)
     v9fs_qtest_pci_add("/virtio/9p/pci/fs/attach/basic", fs_attach);
     v9fs_qtest_pci_add("/virtio/9p/pci/fs/walk/basic", fs_walk);
     v9fs_qtest_pci_add("/virtio/9p/pci/fs/walk/no_slash", fs_walk_no_slash);
+    v9fs_qtest_pci_add("/virtio/9p/pci/fs/walk/dotdot_from_root",
+                       fs_walk_dotdot);
 
     return g_test_run();
 }