hostmem-memfd: add checks before adding hostmem-memfd & properties

Run some memfd-related checks before registering hostmem-memfd &
various properties. This will help libvirt to figure out what the host
is supposed to be capable of.

qemu_memfd_check() is changed to a less optimized version, since it is
used with various flags, it no longer caches the result.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180906161415.8543-1-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

backends/hostmem-memfd.c

@@ -140,6 +140,7 @@ memfd_backend_class_init(ObjectClass *oc, void *data)
 
     bc->alloc = memfd_backend_memory_alloc;
 
+    if (qemu_memfd_check(MFD_HUGETLB)) {
         object_class_property_add_bool(oc, "hugetlb",
                                        memfd_backend_get_hugetlb,
                                        memfd_backend_set_hugetlb,
@@ -148,11 +149,14 @@ memfd_backend_class_init(ObjectClass *oc, void *data)
                                   memfd_backend_get_hugetlbsize,
                                   memfd_backend_set_hugetlbsize,
                                   NULL, NULL, &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);
     }
+}
 
 static const TypeInfo memfd_backend_info = {
     .name = TYPE_MEMORY_BACKEND_MEMFD,
@@ -164,7 +168,9 @@ static const TypeInfo memfd_backend_info = {
 
 static void register_types(void)
 {
+    if (qemu_memfd_check(0)) {
         type_register_static(&memfd_backend_info);
     }
+}
 
 type_init(register_types);

include/qemu/memfd.h

@@ -16,12 +16,28 @@
 #define F_SEAL_WRITE    0x0008  /* prevent writes */
 #endif
 
+#ifndef MFD_CLOEXEC
+#define MFD_CLOEXEC 0x0001U
+#endif
+
+#ifndef MFD_ALLOW_SEALING
+#define MFD_ALLOW_SEALING 0x0002U
+#endif
+
+#ifndef MFD_HUGETLB
+#define MFD_HUGETLB 0x0004U
+#endif
+
+#ifndef MFD_HUGE_SHIFT
+#define MFD_HUGE_SHIFT 26
+#endif
+
 int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
                       uint64_t hugetlbsize, unsigned int seals, Error **errp);
 bool qemu_memfd_alloc_check(void);
 void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
                        int *fd, Error **errp);
 void qemu_memfd_free(void *ptr, size_t size, int fd);
-bool qemu_memfd_check(void);
+bool qemu_memfd_check(unsigned int flags);
 
 #endif /* QEMU_MEMFD_H */

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()) {
+    if (memfd == TEST_MEMFD_AUTO && qemu_memfd_check(0)) {
         memfd = TEST_MEMFD_YES;
     }
 
@@ -903,7 +903,7 @@ static void test_multiqueue(void)
     s->queues = 2;
     test_server_listen(s);
 
-    if (qemu_memfd_check()) {
+    if (qemu_memfd_check(0)) {
         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()) {
+    if (qemu_memfd_check(0)) {
         qtest_add_data_func("/vhost-user/read-guest-mem/memfd",
                             GINT_TO_POINTER(TEST_MEMFD_YES),
                             test_read_guest_mem);

util/memfd.c

@@ -45,22 +45,6 @@ static int memfd_create(const char *name, unsigned int flags)
 }
 #endif
 
-#ifndef MFD_CLOEXEC
-#define MFD_CLOEXEC 0x0001U
-#endif
-
-#ifndef MFD_ALLOW_SEALING
-#define MFD_ALLOW_SEALING 0x0002U
-#endif
-
-#ifndef MFD_HUGETLB
-#define MFD_HUGETLB 0x0004U
-#endif
-
-#ifndef MFD_HUGE_SHIFT
-#define MFD_HUGE_SHIFT 26
-#endif
-
 int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
                       uint64_t hugetlbsize, unsigned int seals, Error **errp)
 {
@@ -201,23 +185,16 @@ bool qemu_memfd_alloc_check(void)
  *
  * Check if host supports memfd.
  */
-bool qemu_memfd_check(void)
+bool qemu_memfd_check(unsigned int flags)
 {
 #ifdef CONFIG_LINUX
-    static int memfd_check = MEMFD_TODO;
+    int mfd = memfd_create("test", flags);
 
-    if (memfd_check == MEMFD_TODO) {
-        int mfd = memfd_create("test", 0);
     if (mfd >= 0) {
-            memfd_check = MEMFD_OK;
         close(mfd);
-        } else {
+        return true;
-            memfd_check = MEMFD_KO;
     }
-    }
-
-    return memfd_check == MEMFD_OK;
-#else
-    return false;
 #endif
+
+    return false;
 }