Re: [PATCH] MdeModulePkg/UefiBootManagerLib: Match the nested partitions

[Laszlo Ersek <lersek@redhat.com>]

On 01/15/19 10:45, Gary Lin wrote:
> In some cases, such as MD RAID1 in Linux, the bootloader may be in a
> nested EFI system partition partition. For example, sda1 and sdb1 are
> combined as md0 and the first partition of md0, md0p1, is an EFI system
> partition. Then, the bootloader can be located by the following device
> paths:
> 
> PCI()/SATA(sda)/Partition(sda1)/Partition(md0p1)/File(bootloader.efi)
> PCI()/SATA(sdb)/Partition(sdb1)/Partition(md0p1)/File(bootloader.efi)

How does edk2 recognize the nested partition md0p1 in the first place?

I would assume that the "outer" partitions (sda1, sdb1) start with some
kind of MD RAID1 header that allows Linux to combine sda1 and sdb1 into
md0p1. How does edk2 get past that header?

Hmmm... based on
<https://raid.wiki.kernel.org/index.php/RAID_superblock_formats>, does
Linux use "footers" instead of "headers"?

Thanks,
Laszlo

> 
> To make the boot option more resilient, we may create a boot option with
> the short-form device path like "Partition(md0p1)/File(bootloader.efi)".
> 
> However, BmMatchPartitionDevicePathNode() only matched the first
> partition node and ignored the nested partitions, so the firmware would
> refuse to load bootloader.efi since "Partition(md0p1)" doesn't match
> either "Partition(sda1)" or "Partition(sda2)".
> 
> This commit modifies BmMatchPartitionDevicePathNode() to iterate all
> nested partitions so that the above boot option could work.
> 
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Cc: Star Zeng <star.zeng@intel.com>
> Cc: Jian J Wang <jian.j.wang@intel.com>
> Cc: Hao Wu <hao.a.wu@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Gary Lin <glin@suse.com>
> ---
>  .../Library/UefiBootManagerLib/BmBoot.c       | 37 ++++++++++++-------
>  1 file changed, 23 insertions(+), 14 deletions(-)
> 
> diff --git a/MdeModulePkg/Library/UefiBootManagerLib/BmBoot.c b/MdeModulePkg/Library/UefiBootManagerLib/BmBoot.c
> index 6a23477eb873..8354c2af674b 100644
> --- a/MdeModulePkg/Library/UefiBootManagerLib/BmBoot.c
> +++ b/MdeModulePkg/Library/UefiBootManagerLib/BmBoot.c
> @@ -1995,21 +1995,30 @@ BmMatchPartitionDevicePathNode (
>      return FALSE;
>    }
>  
> -  //
> -  // See if the harddrive device path in blockio matches the orig Hard Drive Node
> -  //
> -  Node = (HARDDRIVE_DEVICE_PATH *) BlockIoDevicePath;
> +  do {
> +    //
> +    // See if the harddrive device path in blockio matches the orig Hard Drive Node
> +    //
> +    Node = (HARDDRIVE_DEVICE_PATH *) BlockIoDevicePath;
>  
> -  //
> -  // Match Signature and PartitionNumber.
> -  // Unused bytes in Signature are initiaized with zeros.
> -  //
> -  return (BOOLEAN) (
> -    (Node->PartitionNumber == HardDriveDevicePath->PartitionNumber) &&
> -    (Node->MBRType == HardDriveDevicePath->MBRType) &&
> -    (Node->SignatureType == HardDriveDevicePath->SignatureType) &&
> -    (CompareMem (Node->Signature, HardDriveDevicePath->Signature, sizeof (Node->Signature)) == 0)
> -    );
> +    //
> +    // Match Signature and PartitionNumber.
> +    // Unused bytes in Signature are initiaized with zeros.
> +    //
> +    if ((Node->PartitionNumber == HardDriveDevicePath->PartitionNumber) &&
> +        (Node->MBRType == HardDriveDevicePath->MBRType) &&
> +        (Node->SignatureType == HardDriveDevicePath->SignatureType) &&
> +        (CompareMem (Node->Signature, HardDriveDevicePath->Signature, sizeof (Node->Signature)) == 0)) {
> +      return TRUE;
> +    }
> +
> +    // See if a nested partition exists
> +    BlockIoDevicePath = NextDevicePathNode (BlockIoDevicePath);
> +  } while (!IsDevicePathEnd (BlockIoDevicePath) &&
> +           (DevicePathType (BlockIoDevicePath) == MEDIA_DEVICE_PATH) &&
> +           (DevicePathSubType (BlockIoDevicePath) == MEDIA_HARDDRIVE_DP));
> +
> +  return FALSE;
>  }
>  
>  /**
>