tests/qtest/migration: Add a fd + file test

The fd URI supports an fd that is backed by a file. The code should
select between QIOChannelFile and QIOChannelSocket, depending on the
type of the fd. Add a test for that.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20240220224138.24759-4-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>

tests/qtest/migration-test.c

@@ -2433,6 +2433,45 @@ static void test_migrate_precopy_fd_socket(void)
     };
     test_precopy_common(&args);
 }
+
+static void *migrate_precopy_fd_file_start(QTestState *from, QTestState *to)
+{
+    g_autofree char *file = g_strdup_printf("%s/%s", tmpfs, FILE_TEST_FILENAME);
+    int src_flags = O_CREAT | O_RDWR;
+    int dst_flags = O_CREAT | O_RDWR;
+    int fds[2];
+
+    fds[0] = open(file, src_flags, 0660);
+    assert(fds[0] != -1);
+
+    fds[1] = open(file, dst_flags, 0660);
+    assert(fds[1] != -1);
+
+
+    qtest_qmp_fds_assert_success(to, &fds[0], 1,
+                                 "{ 'execute': 'getfd',"
+                                 "  'arguments': { 'fdname': 'fd-mig' }}");
+
+    qtest_qmp_fds_assert_success(from, &fds[1], 1,
+                                 "{ 'execute': 'getfd',"
+                                 "  'arguments': { 'fdname': 'fd-mig' }}");
+
+    close(fds[0]);
+    close(fds[1]);
+
+    return NULL;
+}
+
+static void test_migrate_precopy_fd_file(void)
+{
+    MigrateCommon args = {
+        .listen_uri = "defer",
+        .connect_uri = "fd:fd-mig",
+        .start_hook = migrate_precopy_fd_file_start,
+        .finish_hook = test_migrate_fd_finish_hook
+    };
+    test_file_common(&args, true);
+}
 #endif /* _WIN32 */
 
 static void do_test_validate_uuid(MigrateStart *args, bool should_fail)
@@ -3529,6 +3568,8 @@ int main(int argc, char **argv)
 #ifndef _WIN32
     migration_test_add("/migration/precopy/fd/tcp",
                        test_migrate_precopy_fd_socket);
+    migration_test_add("/migration/precopy/fd/file",
+                       test_migrate_precopy_fd_file);
 #endif
     migration_test_add("/migration/validate_uuid", test_validate_uuid);
     migration_test_add("/migration/validate_uuid_error",