tests/migration-test: Add MEM_TYPE_SHMEM

Add memfd support for mem_type.  Will be used to replace memory_backend.

Reviewed-by: Juraj Marcin <jmarcin@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20251117223908.415965-4-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

tests/qtest/migration/framework.c

@@ -280,6 +280,9 @@ static char *migrate_mem_type_get_opts(MemType type, const char *memory_size)
         backend = g_strdup_printf("-object memory-backend-file,mem-path=%s",
                                   shmem_path);
         break;
+    case MEM_TYPE_MEMFD:
+        backend = g_strdup("-object memory-backend-memfd");
+        break;
     default:
         g_assert_not_reached();
         break;

tests/qtest/migration/framework.h

@@ -19,8 +19,21 @@
 #define FILE_TEST_MARKER 'X'
 
 typedef enum {
+    /*
+     * Use memory-backend-ram, private mappings
+     */
     MEM_TYPE_ANON,
+    /*
+     * Use shmem file (under /dev/shm), shared mappings
+     */
     MEM_TYPE_SHMEM,
+    /*
+     * Use anonymous memfd, shared mappings.
+     *
+     * NOTE: this is internally almost the same as MEM_TYPE_SHMEM on Linux,
+     * but only anonymously allocated.
+     */
+    MEM_TYPE_MEMFD,
     MEM_TYPE_NUM,
 } MemType;