Re: [edk2-devel] Question about Block IO protocol devices

["Andrew Fish" <afish@apple.com>]

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> On Jan 27, 2022, at 6:19 PM, valerij zaporogeci <vlrzprgts@gmail.com> wrote:
> 
> Thank you, Andrew, for the clarification.
> 
>> I don’t remember the use case for HD(0,MBR, sign) type of device path node?
> 
> don't know, how much of usability it would have per se, but
> representing a raw disk this way, would give an easier way to find
> them out. because all such would end with the same 4.1 Type.SubType
> and partition number. without this, a raw disk could be 3.1, or 3.25
> or 3.26 or 3.29 or even 1.4 (VenHw(GUID)) or 1.1 (Pci(2, 0)) as is
> with OVMF for qemu arm64.
> 

In general is it bad to assume what the disk node is going to look like. You have know idea what the transport is going to look like and how that transport enumerates disks. 

As I mentioned the BlockIO protocol instance will tell you if it is for a physical disk or partition via the BlockIo->Media->LogicalPartition member. 

> And yet one thing. The Signature field in the 4.1 typed node for the
> case of GPT for a partition device. Did I understand correctly, that
> its should contain the same GUID as is in the corresponding GUID
> Partition Array entry field UniquePartitionGuid for that partition?
> Because one implementation (not edk2) puts as the Signature field
> DiskGuid in every partition Device Path node.

Yes it is the UniquePartitionGUID
https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Universal/Disk/PartitionDxe/Gpt.c#L389

Thanks,

Andrew Fish




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