greybus: introduce gb_operation_message_init()

Separate the allocation of a message structure from its basic
initialization.  This will allow very common fixed-size operation
response buffers to be allocated from a slab cache.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/operation.c

@@ -301,6 +301,43 @@ gb_hd_message_find(struct greybus_host_device *hd, void *header)
 	return message;
 }
 
+static void gb_operation_message_init(struct greybus_host_device *hd,
+				struct gb_message *message, u16 operation_id,
+				size_t message_size, u8 type)
+{
+	struct gb_operation_msg_hdr *header;
+	u8 *buffer;
+
+	BUG_ON(message_size < sizeof(*header));
+	buffer = &message->buffer[0];
+	header = (struct gb_operation_msg_hdr *)(buffer + hd->buffer_headroom);
+
+	message->header = header;
+	message->payload = header + 1;
+	message->size = message_size;
+
+	/*
+	 * The type supplied for incoming message buffers will be
+	 * 0x00.  Such buffers will be overwritten by arriving data
+	 * so there's no need to initialize the message header.
+	 */
+	if (type) {
+		/*
+		 * For a request, the operation id gets filled in
+		 * when the message is sent.  For a response, it
+		 * will be copied from the request by the caller.
+		 *
+		 * The result field in a request message must be
+		 * zero.  It will be set just prior to sending for
+		 * a response.
+		 */
+		header->size = cpu_to_le16(message_size);
+		header->operation_id = 0;
+		header->type = type;
+		header->result = 0;
+	}
+}
+
 /*
  * Allocate a message to be used for an operation request or response.
  * Both types of message contain a common header.  The request message
@@ -325,7 +362,6 @@ gb_operation_message_alloc(struct greybus_host_device *hd, u8 type,
 	struct gb_operation_msg_hdr *header;
 	size_t message_size = payload_size + sizeof(*header);
 	size_t size;
-	u8 *buffer;
 
 	if (hd->buffer_size_max > GB_OPERATION_MESSAGE_SIZE_MAX) {
 		pr_warn("limiting buffer size to %u\n",
@@ -340,33 +376,9 @@ gb_operation_message_alloc(struct greybus_host_device *hd, u8 type,
 	message = kzalloc(size, gfp_flags);
 	if (!message)
 		return NULL;
-	buffer = &message->buffer[0];
-	header = (struct gb_operation_msg_hdr *)(buffer + hd->buffer_headroom);
 
-	message->header = header;
-	message->payload = header + 1;
-	message->size = message_size;
-
-	/*
-	 * The type supplied for incoming message buffers will be
-	 * 0x00.  Such buffers will be overwritten by arriving data
-	 * so there's no need to initialize the message header.
-	 */
-	if (type) {
-		/*
-		 * For a request, the operation id gets filled in
-		 * when the message is sent.  For a response, it
-		 * will be copied from the request by the caller.
-		 *
-		 * The result field in a request message must be
-		 * zero.  It will be set just prior to sending for
-		 * a response.
-		 */
-		header->size = cpu_to_le16(message_size);
-		header->operation_id = 0;
-		header->type = type;
-		header->result = 0;
-	}
+	/* Initialize the message.  Operation id is filled in later. */
+	gb_operation_message_init(hd, message, 0, message_size, type);
 
 	return message;
 }