efi_loader: correct shortening of device-paths
We use short device-paths in boot options so that a file on a block device
can be found independent of the port into which the device is plugged.
Usb() device-path nodes only contain port and interface information and
therefore cannot identify a block device.
UsbWwi() device-path nodes contain the serial number of USB devices.
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/lib/efi_loader/efi_device_path.c b/lib/efi_loader/efi_device_path.c
index b6dd575..f35f673 100644
--- a/lib/efi_loader/efi_device_path.c
+++ b/lib/efi_loader/efi_device_path.c
@@ -124,17 +124,13 @@
/**
* efi_dp_shorten() - shorten device-path
*
- * We can have device paths that start with a USB WWID or a USB Class node,
- * and a few other cases which don't encode the full device path with bus
- * hierarchy:
+ * When creating a short boot option we want to use a device-path that is
+ * independent of the location where the block device is plugged in.
*
- * * MESSAGING:USB_WWID
- * * MESSAGING:USB_CLASS
- * * MEDIA:FILE_PATH
- * * MEDIA:HARD_DRIVE
- * * MESSAGING:URI
+ * UsbWwi() nodes contain a serial number, hard drive paths a partition
+ * UUID. Both should be unique.
*
- * See UEFI spec (section 3.1.2, about short-form device-paths)
+ * See UEFI spec, section 3.1.2 for "short-form device path".
*
* @dp: original device-path
* @Return: shortened device-path or NULL
@@ -142,12 +138,7 @@
struct efi_device_path *efi_dp_shorten(struct efi_device_path *dp)
{
while (dp) {
- /*
- * TODO: Add MESSAGING:USB_WWID and MESSAGING:URI..
- * in practice fallback.efi just uses MEDIA:HARD_DRIVE
- * so not sure when we would see these other cases.
- */
- if (EFI_DP_TYPE(dp, MESSAGING_DEVICE, MSG_USB) ||
+ if (EFI_DP_TYPE(dp, MESSAGING_DEVICE, MSG_USB_WWI) ||
EFI_DP_TYPE(dp, MEDIA_DEVICE, HARD_DRIVE_PATH) ||
EFI_DP_TYPE(dp, MEDIA_DEVICE, FILE_PATH))
return dp;