On 3/26/23 12:45, Mark Kettenis wrote:
From: Heinrich Schuchardt <heinrich.schucha...@canonical.com>
Date: Sun, 26 Mar 2023 12:25:54 +0200
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.schucha...@canonical.com>
---
include/efi_api.h | 1 +
lib/efi_loader/efi_device_path.c | 21 ++++++---------------
2 files changed, 7 insertions(+), 15 deletions(-)
diff --git a/include/efi_api.h b/include/efi_api.h
index c4512eeb86..dc6e5ce236 100644
--- a/include/efi_api.h
+++ b/include/efi_api.h
@@ -604,6 +604,7 @@ struct efi_device_path_acpi_path {
# define DEVICE_PATH_SUB_TYPE_MSG_MAC_ADDR 0x0b
# define DEVICE_PATH_SUB_TYPE_MSG_UART 0x0e
# define DEVICE_PATH_SUB_TYPE_MSG_USB_CLASS 0x0f
+# define DEVICE_PATH_SUB_TYPE_MSG_USB_WWI 0x10
# define DEVICE_PATH_SUB_TYPE_MSG_SATA 0x12
# define DEVICE_PATH_SUB_TYPE_MSG_NVME 0x17
# define DEVICE_PATH_SUB_TYPE_MSG_URI 0x18
diff --git a/lib/efi_loader/efi_device_path.c b/lib/efi_loader/efi_device_path.c
index 288baa1ca7..9ed5e6273d 100644
--- a/lib/efi_loader/efi_device_path.c
+++ b/lib/efi_loader/efi_device_path.c
@@ -92,17 +92,13 @@ int efi_dp_match(const struct efi_device_path *a,
/**
* 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.
This sentence makes no sense. Do they contain a serial number, a hard
drive path *and* a partition UUID? But then all *three* should be
unique.
* UsbWWi() nodes contain a unique serial number
* HD() nodes contain a unique UUID.
Shortened device paths for files will only be created if the device path
is not a block device. Currently neither the eficonfig nor the efidebug
command allow to specify such a device path.
Best regards
Heinrich
*
- * 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
@@ -110,12 +106,7 @@ int efi_dp_match(const struct efi_device_path *a,
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;
--
2.39.2
