greybus: introduce gb_operation_errno_map()

Define gb_operation_errno_map(), which maps an operation->errno
into the u8 value that represents it in the status field of an
operation response header.  It'll be used in an upcoming patch.

Make gb_operation_status_map() a private function.  It's not used
outside "operation.c" and I don't believe it ever should be.
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/operation.c

@@ -411,7 +411,7 @@ static void gb_operation_message_free(struct gb_message *message)
  * Map an enum gb_operation_status value (which is represented in a
  * message as a single byte) to an appropriate Linux negative errno.
  */
-int gb_operation_status_map(u8 status)
+static int gb_operation_status_map(u8 status)
 {
 	switch (status) {
 	case GB_OP_SUCCESS:
@@ -438,6 +438,39 @@ int gb_operation_status_map(u8 status)
 	}
 }
 
+/*
+ * Map a Linux errno value (from operation->errno) into the value
+ * that should represent it in a response message status sent
+ * over the wire.  Returns an enum gb_operation_status value (which
+ * is represented in a message as a single byte).
+ */
+static u8 gb_operation_errno_map(int errno)
+{
+	switch (errno) {
+	case 0:
+		return GB_OP_SUCCESS;
+	case -EINTR:
+		return GB_OP_INTERRUPTED;
+	case -ETIMEDOUT:
+		return GB_OP_TIMEOUT;
+	case -ENOMEM:
+		return GB_OP_NO_MEMORY;
+	case -EPROTONOSUPPORT:
+		return GB_OP_PROTOCOL_BAD;
+	case -EMSGSIZE:
+		return GB_OP_OVERFLOW;	/* Could be underflow too */
+	case -EINVAL:
+		return GB_OP_INVALID;
+	case -EAGAIN:
+		return GB_OP_RETRY;
+	case -EILSEQ:
+		return GB_OP_MALFUNCTION;
+	case -EIO:
+	default:
+		return GB_OP_UNKNOWN_ERROR;
+	}
+}
+
 /*
  * Create a Greybus operation to be sent over the given connection.
  * The request buffer will be big enough for a payload of the given
@@ -656,6 +689,7 @@ int gb_operation_response_send(struct gb_operation *operation, int errno)
 		pr_err("request result already set\n");
 		return -EIO;	/* Shouldn't happen */
 	}
+	(void)gb_operation_errno_map;	/* avoid a build warning */
 	gb_operation_destroy(operation);
 
 	return 0;

drivers/staging/greybus/operation.h

@@ -104,8 +104,6 @@ int gb_operation_response_send(struct gb_operation *operation, int errno);
 
 void gb_operation_cancel(struct gb_operation *operation, int errno);
 
-int gb_operation_status_map(u8 status);
-
 void greybus_data_sent(struct greybus_host_device *hd,
 				void *header, int status);