efi_loader: provide function to get last node of a device path

On a block device and its partitions the same protocols can be
installed. To tell the apart we can use the type of the last
node of the device path which is not the end node.

The patch provides a utility function to find this last node.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>

include/efi_loader.h

@@ -312,6 +312,9 @@ struct efi_device_path *efi_dp_from_eth(void);
 struct efi_device_path *efi_dp_from_mem(uint32_t mem_type,
 					uint64_t start_address,
 					uint64_t end_address);
+/* Determine the last device path node that is not the end node. */
+const struct efi_device_path *efi_dp_last_node(
+			const struct efi_device_path *dp);
 efi_status_t efi_dp_split_file_path(struct efi_device_path *full_path,
 				    struct efi_device_path **device_path,
 				    struct efi_device_path **file_path);

lib/efi_loader/efi_device_path.c

@@ -208,6 +208,26 @@ struct efi_object *efi_dp_find_obj(struct efi_device_path *dp,
 	return efiobj;
 }
 
+/*
+ * Determine the last device path node that is not the end node.
+ *
+ * @dp		device path
+ * @return	last node before the end node if it exists
+ *		otherwise NULL
+ */
+const struct efi_device_path *efi_dp_last_node(const struct efi_device_path *dp)
+{
+	struct efi_device_path *ret;
+
+	if (!dp || dp->type == DEVICE_PATH_TYPE_END)
+		return NULL;
+	while (dp) {
+		ret = (struct efi_device_path *)dp;
+		dp = efi_dp_next(dp);
+	}
+	return ret;
+}
+
 /* return size not including End node: */
 unsigned efi_dp_size(const struct efi_device_path *dp)
 {