tests/qtest/migration: Add a test for mapped-ram with passing of fds

Add a multifd test for mapped-ram with passing of fds into QEMU. This
is how libvirt will consume the feature.

There are a couple of details to the fdset mechanism:

- multifd needs two distinct file descriptors (not duplicated with
  dup()) so it can enable O_DIRECT only on the channels that do
  aligned IO. The dup() system call creates file descriptors that
  share status flags, of which O_DIRECT is one.

- the open() access mode flags used for the fds passed into QEMU need
  to match the flags QEMU uses to open the file. Currently O_WRONLY
  for src and O_RDONLY for dst.

Note that fdset code goes under _WIN32 because fd passing is not
supported on Windows.

Reviewed-by: Peter Xu <peterx@redhat.com>
[brought back the qmp_remove_fd() call at the end of the tests]
Signed-off-by: Fabiano Rosas <farosas@suse.de>

tests/qtest/migration-test.c

@@ -2104,11 +2104,18 @@ static void test_precopy_file(void)
 
 #ifndef _WIN32
 static void fdset_add_fds(QTestState *qts, const char *file, int flags,
-                          int num_fds)
+                          int num_fds, bool direct_io)
 {
     for (int i = 0; i < num_fds; i++) {
         int fd;
 
+#ifdef O_DIRECT
+        /* only secondary channels can use direct-io */
+        if (direct_io && i != 0) {
+            flags |= O_DIRECT;
+        }
+#endif
+
         fd = open(file, flags, 0660);
         assert(fd != -1);
 
@@ -2122,8 +2129,8 @@ static void *file_offset_fdset_start_hook(QTestState *from, QTestState *to)
 {
     g_autofree char *file = g_strdup_printf("%s/%s", tmpfs, FILE_TEST_FILENAME);
 
-    fdset_add_fds(from, file, O_WRONLY, 1);
+    fdset_add_fds(from, file, O_WRONLY, 1, false);
-    fdset_add_fds(to, file, O_RDONLY, 1);
+    fdset_add_fds(to, file, O_RDONLY, 1, false);
 
     return NULL;
 }
@@ -2295,6 +2302,91 @@ static void test_multifd_file_mapped_ram_dio(void)
     test_file_common(&args, true);
 }
 
+#ifndef _WIN32
+static void multifd_mapped_ram_fdset_end(QTestState *from, QTestState *to,
+                                         void *opaque)
+{
+    QDict *resp;
+    QList *fdsets;
+
+    /*
+     * Remove the fdsets after migration, otherwise a second migration
+     * would fail due fdset reuse.
+     */
+    qtest_qmp_assert_success(from, "{'execute': 'remove-fd', "
+                             "'arguments': { 'fdset-id': 1}}");
+
+    /*
+     * Make sure no fdsets are left after migration, otherwise a
+     * second migration would fail due fdset reuse.
+     */
+    resp = qtest_qmp(from, "{'execute': 'query-fdsets', "
+                     "'arguments': {}}");
+    g_assert(qdict_haskey(resp, "return"));
+    fdsets = qdict_get_qlist(resp, "return");
+    g_assert(fdsets && qlist_empty(fdsets));
+}
+
+static void *multifd_mapped_ram_fdset_dio(QTestState *from, QTestState *to)
+{
+    g_autofree char *file = g_strdup_printf("%s/%s", tmpfs, FILE_TEST_FILENAME);
+
+    fdset_add_fds(from, file, O_WRONLY, 2, true);
+    fdset_add_fds(to, file, O_RDONLY, 2, true);
+
+    migrate_multifd_mapped_ram_start(from, to);
+    migrate_set_parameter_bool(from, "direct-io", true);
+    migrate_set_parameter_bool(to, "direct-io", true);
+
+    return NULL;
+}
+
+static void *multifd_mapped_ram_fdset(QTestState *from, QTestState *to)
+{
+    g_autofree char *file = g_strdup_printf("%s/%s", tmpfs, FILE_TEST_FILENAME);
+
+    fdset_add_fds(from, file, O_WRONLY, 2, false);
+    fdset_add_fds(to, file, O_RDONLY, 2, false);
+
+    migrate_multifd_mapped_ram_start(from, to);
+
+    return NULL;
+}
+
+static void test_multifd_file_mapped_ram_fdset(void)
+{
+    g_autofree char *uri = g_strdup_printf("file:/dev/fdset/1,offset=%d",
+                                           FILE_TEST_OFFSET);
+    MigrateCommon args = {
+        .connect_uri = uri,
+        .listen_uri = "defer",
+        .start_hook = multifd_mapped_ram_fdset,
+        .finish_hook = multifd_mapped_ram_fdset_end,
+    };
+
+    test_file_common(&args, true);
+}
+
+static void test_multifd_file_mapped_ram_fdset_dio(void)
+{
+    g_autofree char *uri = g_strdup_printf("file:/dev/fdset/1,offset=%d",
+                                           FILE_TEST_OFFSET);
+    MigrateCommon args = {
+        .connect_uri = uri,
+        .listen_uri = "defer",
+        .start_hook = multifd_mapped_ram_fdset_dio,
+        .finish_hook = multifd_mapped_ram_fdset_end,
+    };
+
+    if (!probe_o_direct_support(tmpfs)) {
+        g_test_skip("Filesystem does not support O_DIRECT");
+        return;
+    }
+
+    test_file_common(&args, true);
+}
+#endif /* !_WIN32 */
+
 static void test_precopy_tcp_plain(void)
 {
     MigrateCommon args = {
@@ -3736,6 +3828,13 @@ int main(int argc, char **argv)
     migration_test_add("/migration/multifd/file/mapped-ram/dio",
                        test_multifd_file_mapped_ram_dio);
 
+#ifndef _WIN32
+    migration_test_add("/migration/multifd/file/mapped-ram/fdset",
+                       test_multifd_file_mapped_ram_fdset);
+    migration_test_add("/migration/multifd/file/mapped-ram/fdset/dio",
+                       test_multifd_file_mapped_ram_fdset_dio);
+#endif
+
 #ifdef CONFIG_GNUTLS
     migration_test_add("/migration/precopy/unix/tls/psk",
                        test_precopy_unix_tls_psk);