Re: GRUB issue on device priority

[Leif Lindholm <leif.lindholm@linaro.org>]

On Tue, Nov 07, 2017 at 10:02:30PM +0800, Haojian Zhuang wrote:
> Hi all,
> 
> It seems there's a device priority issue in GRUB.

GRUB is behaving as expected.

> All block io handles are linked into the list in edk2, and GRUB could fetch
> it. Then GRUB creates its own ascending on HD priority.
> add_device():
>   for (p = devices; *p; p = &((*p)->next)) {
>     ret = grub_efi_compare_device_paths (grub_efi_find_last_device_path
> ((*p->device_path),
>                          grub_efi_find_last_device_path->device_path));
>     if (ret == 0) {
>       ret = grub_efi_compare_device_paths ((*p)->device_path,
>                                            d->device_path);
>     }
>     if (ret == 0) {
>       return;
>     } else if (ret > 0) {
>       break;
>     }
>   }
>   ...

UEFI guarantees no ordering of block devices. GRUB is a UEFI
application, so it cannot assume anything with regards to device
ordering.

> In the HiKey platform, I prepared the same driver for both eMMC and
> SD. So the device paths are in below.
> SD: /HardwareVendor(0d51905b-b77e-452a-a2c0-eca0cc8d514a)[9: 00 e0 23 f7 00 00 00 00 00 ]/UnknownMessaging(1a)/EndEntire
> eMMC: /HardwareVendor(0d51905b-b77e-452a-a2c0-eca0cc8d514a)[9: 00 d0 23 f7 00 00 00 00 00]/UnknownMessaging(1d)/Ctrl(0)/EndEntire
> 
> #define MSG_SD_DP                   0x1A
> #define MSG_EMMC_DP                 0x1D
> 
> In the second level, the device paths are different.
> 
> And GRUB resort the sequence by ascending order (with above
> code). So SD device always gets higher priority than eMMC device.
> 
> If we always use installer to install OS, it may not an issue. Since
> installer could create grub.cfg by itself. But it imports another
> issue on lacking of persistent variable storage. And we need to
> deploy system without installer on embedded device.

Yes, this is the bit which is interesting, and why I requested you
post this problem to edk2-devel.

I believe that we need to have a sensible way to deal with embedded
platforms that do not have operating systems "installed" to them, but
rather written as images to flash devices.

So, can you clarify a few things for me?:
- Where is GRUB located in your (pre-SD) system?
- Where is GRUB located in your SD system?
- Are you looking for a way to support GRUB being located on either
  eMMC or SD? Or are you looking to always have GRUB loaded from eMMC?

/
    Leif