hostmem: add file-based HostMemoryBackend

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

MST: comment tweak

backends/Makefile.objs

@@ -8,3 +8,4 @@ baum.o-cflags := $(SDL_CFLAGS)
 common-obj-$(CONFIG_TPM) += tpm.o
 
 common-obj-y += hostmem.o hostmem-ram.o
+common-obj-$(CONFIG_LINUX) += hostmem-file.o

backends/hostmem-file.c

@@ -0,0 +1,107 @@
+/*
+ * QEMU Host Memory Backend for hugetlbfs
+ *
+ * Copyright (C) 2013-2014 Red Hat Inc
+ *
+ * Authors:
+ *   Paolo Bonzini <pbonzini@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+#include "sysemu/hostmem.h"
+#include "qom/object_interfaces.h"
+
+/* hostmem-file.c */
+/**
+ * @TYPE_MEMORY_BACKEND_FILE:
+ * name of backend that uses mmap on a file descriptor
+ */
+#define TYPE_MEMORY_BACKEND_FILE "memory-backend-file"
+
+#define MEMORY_BACKEND_FILE(obj) \
+    OBJECT_CHECK(HostMemoryBackendFile, (obj), TYPE_MEMORY_BACKEND_FILE)
+
+typedef struct HostMemoryBackendFile HostMemoryBackendFile;
+
+struct HostMemoryBackendFile {
+    HostMemoryBackend parent_obj;
+    char *mem_path;
+};
+
+static void
+file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
+{
+    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(backend);
+
+    if (!backend->size) {
+        error_setg(errp, "can't create backend with size 0");
+        return;
+    }
+    if (!fb->mem_path) {
+        error_setg(errp, "mem_path property not set");
+        return;
+    }
+#ifndef CONFIG_LINUX
+    error_setg(errp, "-mem-path not supported on this host");
+#else
+    if (!memory_region_size(&backend->mr)) {
+        memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),
+                                 object_get_canonical_path(OBJECT(backend)),
+                                 backend->size,
+                                 fb->mem_path, errp);
+    }
+#endif
+}
+
+static void
+file_backend_class_init(ObjectClass *oc, void *data)
+{
+    HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
+
+    bc->alloc = file_backend_memory_alloc;
+}
+
+static char *get_mem_path(Object *o, Error **errp)
+{
+    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
+
+    return g_strdup(fb->mem_path);
+}
+
+static void set_mem_path(Object *o, const char *str, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(o);
+    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
+
+    if (memory_region_size(&backend->mr)) {
+        error_setg(errp, "cannot change property value");
+        return;
+    }
+    if (fb->mem_path) {
+        g_free(fb->mem_path);
+    }
+    fb->mem_path = g_strdup(str);
+}
+
+static void
+file_backend_instance_init(Object *o)
+{
+    object_property_add_str(o, "mem-path", get_mem_path,
+                            set_mem_path, NULL);
+}
+
+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_size = sizeof(HostMemoryBackendFile),
+};
+
+static void register_types(void)
+{
+    type_register_static(&file_backend_info);
+}
+
+type_init(register_types);