[PATCH v7 1/5] hw/nvram/fw_cfg: Add the FW_CFG_DATA_GENERATOR interface

[Philippe Mathieu-Daudé]

The FW_CFG_DATA_GENERATOR allows any object to produce
blob of data consumable by the fw_cfg device.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
v7: addressed Laszlo's comments
- fixed typos in description
- return size_t instead of ssize_t; 0 for error
- do not use 1-letter variable names
- do not open-code 'fw_cfg-data-generator'
- cast g_memdup() size argument as 'guint'
- improved documentation
---
 docs/specs/fw_cfg.txt     |  9 ++++++-
 include/hw/nvram/fw_cfg.h | 52 +++++++++++++++++++++++++++++++++++++++
 hw/nvram/fw_cfg.c         | 31 +++++++++++++++++++++++
 3 files changed, 91 insertions(+), 1 deletion(-)

diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt
index 8f1ebc66fa..bc16daa38a 100644
--- a/docs/specs/fw_cfg.txt
+++ b/docs/specs/fw_cfg.txt
@@ -219,7 +219,7 @@ To check the result, read the "control" field:
 
 = Externally Provided Items =
 
-As of v2.4, "file" fw_cfg items (i.e., items with selector keys above
+Since v2.4, "file" fw_cfg items (i.e., items with selector keys above
 FW_CFG_FILE_FIRST, and with a corresponding entry in the fw_cfg file
 directory structure) may be inserted via the QEMU command line, using
 the following syntax:
@@ -230,6 +230,13 @@ Or
 
     -fw_cfg [name=]<item_name>,string=<string>
 
+Since v5.1, QEMU allows some objects to generate fw_cfg-specific content,
+the content is then associated with a "file" item using the 'gen_id' option
+in the command line, using the following syntax:
+
+    -object <generator-type>,id=<generated_id>,[generator-specific-options] \
+    -fw_cfg [name=]<item_name>,gen_id=<generated_id>
+
 See QEMU man page for more documentation.
 
 Using item_name with plain ASCII characters only is recommended.
diff --git a/include/hw/nvram/fw_cfg.h b/include/hw/nvram/fw_cfg.h
index 25d9307018..8fbf2446c1 100644
--- a/include/hw/nvram/fw_cfg.h
+++ b/include/hw/nvram/fw_cfg.h
@@ -9,11 +9,43 @@
 #define TYPE_FW_CFG     "fw_cfg"
 #define TYPE_FW_CFG_IO  "fw_cfg_io"
 #define TYPE_FW_CFG_MEM "fw_cfg_mem"
+#define TYPE_FW_CFG_DATA_GENERATOR_INTERFACE "fw_cfg-data-generator"
 
 #define FW_CFG(obj)     OBJECT_CHECK(FWCfgState,    (obj), TYPE_FW_CFG)
 #define FW_CFG_IO(obj)  OBJECT_CHECK(FWCfgIoState,  (obj), TYPE_FW_CFG_IO)
 #define FW_CFG_MEM(obj) OBJECT_CHECK(FWCfgMemState, (obj), TYPE_FW_CFG_MEM)
 
+#define FW_CFG_DATA_GENERATOR_CLASS(class) \
+    OBJECT_CLASS_CHECK(FWCfgDataGeneratorClass, (class), \
+                       TYPE_FW_CFG_DATA_GENERATOR_INTERFACE)
+#define FW_CFG_DATA_GENERATOR_GET_CLASS(obj) \
+    OBJECT_GET_CLASS(FWCfgDataGeneratorClass, (obj), \
+                     TYPE_FW_CFG_DATA_GENERATOR_INTERFACE)
+
+typedef struct FWCfgDataGeneratorClass {
+    /*< private >*/
+    InterfaceClass parent_class;
+    /*< public >*/
+
+    /**
+     * get_data:
+     * @obj: the object implementing this interface
+     *
+     * Returns: pointer to start of the generated item data
+     *
+     * The returned pointer is a QObject weak reference, @obj owns
+     * the reference and may free it at any time in the future.
+     */
+    const void *(*get_data)(Object *obj);
+    /**
+     * get_length:
+     * @obj: the object implementing this interface
+     *
+     * Returns: the size of the generated item data in bytes
+     */
+    size_t (*get_length)(Object *obj);
+} FWCfgDataGeneratorClass;
+
 typedef struct fw_cfg_file FWCfgFile;
 
 #define FW_CFG_ORDER_OVERRIDE_VGA    70
@@ -263,6 +295,26 @@ void fw_cfg_add_file_callback(FWCfgState *s, const char 
*filename,
 void *fw_cfg_modify_file(FWCfgState *s, const char *filename, void *data,
                          size_t len);
 
+/**
+ * fw_cfg_add_from_generator:
+ * @s: fw_cfg device being modified
+ * @filename: name of new fw_cfg file item
+ * @gen_id: name of object implementing FW_CFG_DATA_GENERATOR interface
+ * @errp: pointer to a NULL initialized error object
+ *
+ * Add a new NAMED fw_cfg item with the content generated from the
+ * @gen_id object. The data generated by the @gen_id object/ is copied
+ * into the data structure of the fw_cfg device.
+ * The next available (unused) selector key starting at FW_CFG_FILE_FIRST
+ * will be used; also, a new entry will be added to the file directory
+ * structure residing at key value FW_CFG_FILE_DIR, containing the item name,
+ * data size, and assigned selector key value.
+ *
+ * Returns: the size of the device tree image on success, or 0 on errors.
+ */
+size_t fw_cfg_add_from_generator(FWCfgState *s, const char *filename,
+                                 const char *gen_id, Error **errp);
+
 FWCfgState *fw_cfg_init_io_dma(uint32_t iobase, uint32_t dma_iobase,
                                 AddressSpace *dma_as);
 FWCfgState *fw_cfg_init_io(uint32_t iobase);
diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
index 8dd50c2c72..6d2fa13042 100644
--- a/hw/nvram/fw_cfg.c
+++ b/hw/nvram/fw_cfg.c
@@ -1032,6 +1032,31 @@ void *fw_cfg_modify_file(FWCfgState *s, const char 
*filename,
     return NULL;
 }
 
+size_t fw_cfg_add_from_generator(FWCfgState *s, const char *filename,
+                                 const char *gen_id, Error **errp)
+{
+    FWCfgDataGeneratorClass *klass;
+    Object *obj;
+    size_t size;
+
+    obj = object_resolve_path_component(object_get_objects_root(), gen_id);
+    if (!obj) {
+        error_setg(errp, "Cannot find object ID %s", gen_id);
+        return 0;
+    }
+    if (!object_dynamic_cast(obj, TYPE_FW_CFG_DATA_GENERATOR_INTERFACE)) {
+        error_setg(errp, "Object '%s' is not a '%s' subclass",
+                   TYPE_FW_CFG_DATA_GENERATOR_INTERFACE, gen_id);
+        return 0;
+    }
+    klass = FW_CFG_DATA_GENERATOR_GET_CLASS(obj);
+    size = klass->get_length(obj);
+    fw_cfg_add_file(s, filename, g_memdup(klass->get_data(obj), (guint)size),
+                    size);
+
+    return size;
+}
+
 static void fw_cfg_machine_reset(void *opaque)
 {
     MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
@@ -1333,12 +1358,18 @@ static const TypeInfo fw_cfg_mem_info = {
     .class_init    = fw_cfg_mem_class_init,
 };
 
+static const TypeInfo fw_cfg_data_generator_interface_info = {
+    .name = TYPE_FW_CFG_DATA_GENERATOR_INTERFACE,
+    .parent = TYPE_INTERFACE,
+    .class_size = sizeof(FWCfgDataGeneratorClass),
+};
 
 static void fw_cfg_register_types(void)
 {
     type_register_static(&fw_cfg_info);
     type_register_static(&fw_cfg_io_info);
     type_register_static(&fw_cfg_mem_info);
+    type_register_static(&fw_cfg_data_generator_interface_info);
 }
 
 type_init(fw_cfg_register_types)
-- 
2.21.3