[5/5] hostmem-file: Add "persistent" option

diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index d078775b4b..e6cb232349 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -32,6 +32,7 @@  struct HostMemoryBackendFile {
     HostMemoryBackend parent_obj;
 
     bool share;
+    bool persistent;
     char *mem_path;
 };
 
@@ -57,7 +58,7 @@  file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
         path = object_get_canonical_path(OBJECT(backend));
         memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),
                                  path,
-                                 backend->size, fb->share, true,
+                                 backend->size, fb->share, fb->persistent,
                                  fb->mem_path, errp);
         g_free(path);
     }
@@ -103,6 +104,26 @@  static void file_memory_backend_set_share(Object *o, bool value, Error **errp)
     fb->share = value;
 }
 
+static bool file_memory_backend_get_persistent(Object *o, Error **errp)
+{
+    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
+
+    return fb->persistent;
+}
+
+static void file_memory_backend_set_persistent(Object *o, bool value,
+                                               Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(o);
+    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
+
+    if (host_memory_backend_mr_inited(backend)) {
+        error_setg(errp, "cannot change property value");
+        return;
+    }
+    fb->persistent = value;
+}
+
 static void
 file_backend_class_init(ObjectClass *oc, void *data)
 {
@@ -110,14 +131,25 @@  file_backend_class_init(ObjectClass *oc, void *data)
 
     bc->alloc = file_backend_memory_alloc;
 
+
     object_class_property_add_bool(oc, "share",
         file_memory_backend_get_share, file_memory_backend_set_share,
         &error_abort);
+    object_class_property_add_bool(oc, "persistent",
+        file_memory_backend_get_persistent, file_memory_backend_set_persistent,
+        &error_abort);
     object_class_property_add_str(oc, "mem-path",
         get_mem_path, set_mem_path,
         &error_abort);
 }
 
+static void file_backend_instance_init(Object *o)
+{
+    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
+
+    fb->persistent = true;
+}
+
 static void file_backend_instance_finalize(Object *o)
 {
     HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
@@ -129,6 +161,7 @@  static const TypeInfo file_backend_info = {
     .name = TYPE_MEMORY_BACKEND_FILE,
     .parent = TYPE_MEMORY_BACKEND,
     .class_init = file_backend_class_init,
+    .instance_init = file_backend_instance_init,
     .instance_finalize = file_backend_instance_finalize,
     .instance_size = sizeof(HostMemoryBackendFile),
 };
diff --git a/qemu-options.hx b/qemu-options.hx
index 30c4f9850f..7fb4feec9b 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -3961,7 +3961,7 @@  property must be set.  These objects are placed in the
 
 @table @option
 
-@item -object memory-backend-file,id=@var{id},size=@var{size},mem-path=@var{dir},share=@var{on|off}
+@item -object memory-backend-file,id=@var{id},size=@var{size},mem-path=@var{dir},share=@var{on|off},persistent=@var{on|off}
 
 Creates a memory file backend object, which can be used to back
 the guest RAM with huge pages. The @option{id} parameter is a
@@ -3973,6 +3973,13 @@  the path to either a shared memory or huge page filesystem mount.
 The @option{share} boolean option determines whether the memory
 region is marked as private to QEMU, or shared. The latter allows
 a co-operating external process to access the QEMU memory region.
+Setting the @option{persistent} boolean option to @var{off}
+indicates that memory contents can be safely discarded and not
+flushed to disk when the backend object is destroyed or QEMU
+exits.  @option{persistent} is @var{on} by default.  It is valid
+to set @option{persistent} to @var{off} if @option{share} is
+@var{on}. It is redundant to set @option{persistent} to @var{off}
+if @option{share} is @var{off}.
 
 @item -object rng-random,id=@var{id},filename=@var{/dev/random}