[Qemu-devel] [PATCH v2 1/4] hostmem-memfd: disable for systems wihtout sealing support

[Ilya Maximets]

If seals are not supported, memfd_create() will fail.
Furthermore, there is no way to disable it in this case because
'.seal' property is not registered.

This issue leads to vhost-user-test failures on RHEL 7.2:

  qemu-system-x86_64: -object memory-backend-memfd,id=mem,size=2M,: \
                      failed to create memfd: Invalid argument

and actually breaks the feature on such systems.

Let's restrict memfd backend to systems with sealing support.

Signed-off-by: Ilya Maximets <i.maxim...@samsung.com>
---
 backends/hostmem-memfd.c | 18 ++++++++----------
 tests/vhost-user-test.c  |  6 +++---
 2 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
index b6836b28e5..a3455da9c9 100644
--- a/backends/hostmem-memfd.c
+++ b/backends/hostmem-memfd.c
@@ -156,15 +156,13 @@ memfd_backend_class_init(ObjectClass *oc, void *data)
                                               "Huge pages size (ex: 2M, 1G)",
                                               &error_abort);
     }
-    if (qemu_memfd_check(MFD_ALLOW_SEALING)) {
-        object_class_property_add_bool(oc, "seal",
-                                       memfd_backend_get_seal,
-                                       memfd_backend_set_seal,
-                                       &error_abort);
-        object_class_property_set_description(oc, "seal",
-                                              "Seal growing & shrinking",
-                                              &error_abort);
-    }
+    object_class_property_add_bool(oc, "seal",
+                                   memfd_backend_get_seal,
+                                   memfd_backend_set_seal,
+                                   &error_abort);
+    object_class_property_set_description(oc, "seal",
+                                          "Seal growing & shrinking",
+                                          &error_abort);
 }
 
 static const TypeInfo memfd_backend_info = {
@@ -177,7 +175,7 @@ static const TypeInfo memfd_backend_info = {
 
 static void register_types(void)
 {
-    if (qemu_memfd_check(0)) {
+    if (qemu_memfd_check(MFD_ALLOW_SEALING)) {
         type_register_static(&memfd_backend_info);
     }
 }
diff --git a/tests/vhost-user-test.c b/tests/vhost-user-test.c
index 45d58d8ea2..e3e9a33580 100644
--- a/tests/vhost-user-test.c
+++ b/tests/vhost-user-test.c
@@ -169,7 +169,7 @@ static char *get_qemu_cmd(TestServer *s,
                           int mem, enum test_memfd memfd, const char *mem_path,
                           const char *chr_opts, const char *extra)
 {
-    if (memfd == TEST_MEMFD_AUTO && qemu_memfd_check(0)) {
+    if (memfd == TEST_MEMFD_AUTO && qemu_memfd_check(MFD_ALLOW_SEALING)) {
         memfd = TEST_MEMFD_YES;
     }
 
@@ -903,7 +903,7 @@ static void test_multiqueue(void)
     s->queues = 2;
     test_server_listen(s);
 
-    if (qemu_memfd_check(0)) {
+    if (qemu_memfd_check(MFD_ALLOW_SEALING)) {
         cmd = g_strdup_printf(
             QEMU_CMD_MEMFD QEMU_CMD_CHR QEMU_CMD_NETDEV ",queues=%d "
             "-device virtio-net-pci,netdev=net0,mq=on,vectors=%d",
@@ -963,7 +963,7 @@ int main(int argc, char **argv)
     /* run the main loop thread so the chardev may operate */
     thread = g_thread_new(NULL, thread_function, loop);
 
-    if (qemu_memfd_check(0)) {
+    if (qemu_memfd_check(MFD_ALLOW_SEALING)) {
         qtest_add_data_func("/vhost-user/read-guest-mem/memfd",
                             GINT_TO_POINTER(TEST_MEMFD_YES),
                             test_read_guest_mem);
-- 
2.17.1