[Qemu-devel] [PATCH v3 0/4] memfd fixes.

[Qemu-devel] [PATCH v3 0/4] memfd fixes.

[Ilya Maximets]

Version 3:
    * Rebase on top of current master.

Version 2:
    * First patch changed to just drop the memfd backend
      if seals are not supported.

Ilya Maximets (4):
  hostmem-memfd: disable for systems wihtout sealing support
  memfd: always check for MFD_CLOEXEC
  memfd: set up correct errno if not supported
  memfd: improve error messages

 backends/hostmem-memfd.c | 18 ++++++++----------
 tests/vhost-user-test.c  |  5 +++--
 util/memfd.c             | 10 ++++++++--
 3 files changed, 19 insertions(+), 14 deletions(-)

-- 
2.17.1

[Qemu-devel] [PATCH v3 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.maximets@samsung.com>
---
 backends/hostmem-memfd.c | 18 ++++++++----------
 tests/vhost-user-test.c  |  5 +++--
 2 files changed, 11 insertions(+), 12 deletions(-)

diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c
index 98c9bf3240..46b15b916a 100644
--- a/backends/hostmem-memfd.c
+++ b/backends/hostmem-memfd.c
@@ -154,15 +154,13 @@ 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 = {
@@ -175,7 +173,7 @@ 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 0c965b3b1e..3817966010 100644
--- a/tests/vhost-user-test.c
+++ b/tests/vhost-user-test.c
@@ -178,7 +178,8 @@ static void append_mem_opts(TestServer *server, GString *cmd_line,
                             int size, enum test_memfd memfd)
 {
     if (memfd == TEST_MEMFD_AUTO) {
-        memfd = qemu_memfd_check(0) ? TEST_MEMFD_YES : TEST_MEMFD_NO;
+        memfd = qemu_memfd_check(MFD_ALLOW_SEALING) ? TEST_MEMFD_YES
+                                                    : TEST_MEMFD_NO;
     }
 
     if (memfd == TEST_MEMFD_YES) {
@@ -930,7 +931,7 @@ static void register_vhost_user_test(void)
                  "virtio-net",
                  test_read_guest_mem, &opts);
 
-    if (qemu_memfd_check(0)) {
+    if (qemu_memfd_check(MFD_ALLOW_SEALING)) {
         opts.before = vhost_user_test_setup_memfd;
         qos_add_test("vhost-user/read-guest-mem/memfd",
                      "virtio-net",
-- 
2.17.1

[Qemu-devel] [PATCH v3 2/4] memfd: always check for MFD_CLOEXEC

[Ilya Maximets]

QEMU always sets this flag unconditionally. We need to
check if it's supported.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 util/memfd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/util/memfd.c b/util/memfd.c
index 8debd0d037..d74ce4d793 100644
--- a/util/memfd.c
+++ b/util/memfd.c
@@ -188,7 +188,7 @@ bool qemu_memfd_alloc_check(void)
 bool qemu_memfd_check(unsigned int flags)
 {
 #ifdef CONFIG_LINUX
-    int mfd = memfd_create("test", flags);
+    int mfd = memfd_create("test", flags | MFD_CLOEXEC);
 
     if (mfd >= 0) {
         close(mfd);
-- 
2.17.1

[Qemu-devel] [PATCH v3 3/4] memfd: set up correct errno if not supported

[Ilya Maximets]

qemu_memfd_create() prints the value of 'errno' which is not
set in this case.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 util/memfd.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/util/memfd.c b/util/memfd.c
index d74ce4d793..393d23da96 100644
--- a/util/memfd.c
+++ b/util/memfd.c
@@ -40,6 +40,7 @@ static int memfd_create(const char *name, unsigned int flags)
 #ifdef __NR_memfd_create
     return syscall(__NR_memfd_create, name, flags);
 #else
+    errno = ENOSYS;
     return -1;
 #endif
 }
-- 
2.17.1

[Qemu-devel] [PATCH v3 4/4] memfd: improve error messages

[Ilya Maximets]

This gives more information about the failure.
Additionally 'ENOSYS' returned for a non-Linux platforms instead of
'errno', which is not initilaized in this case.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 util/memfd.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/util/memfd.c b/util/memfd.c
index 393d23da96..00334e5b21 100644
--- a/util/memfd.c
+++ b/util/memfd.c
@@ -71,14 +71,18 @@ int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
     }
     mfd = memfd_create(name, flags);
     if (mfd < 0) {
+        error_setg_errno(errp, errno,
+                         "failed to create memfd with flags 0x%x", flags);
         goto err;
     }
 
     if (ftruncate(mfd, size) == -1) {
+        error_setg_errno(errp, errno, "failed to resize memfd to %zu", size);
         goto err;
     }
 
     if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
+        error_setg_errno(errp, errno, "failed to add seals 0x%x", seals);
         goto err;
     }
 
@@ -88,8 +92,9 @@ err:
     if (mfd >= 0) {
         close(mfd);
     }
+#else
+    error_setg_errno(errp, ENOSYS, "failed to create memfd");
 #endif
-    error_setg_errno(errp, errno, "failed to create memfd");
     return -1;
 }
 
-- 
2.17.1