Functionality issues in UDF support

["Ni, Ruiyu" <ruiyu.ni@intel.com>]

Paulo,
Before raising my questions, I'd like to confirm that for a single CD/DVD in UDF format, there might be multiple volumes.
One of the volume could be Eltorito type.
If my understanding is correct, please continue reading below.

We found below mapping table using "map -r" shell command in a platform with only PartitionDxe change and without UdfDxe driver.
It's a bug that <BLK6> and <BLK7/FS2> are created. Actually they are identical to <BLK3> and <BLK4/FS1>.

--- Mapping table---
     BLK2: Alias(s):
          PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x0,0xFFFF,0x0)

     BLK3: Alias(s):
          PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x0,0xFFFF,0x0)/CDROM(0x0)
      FS1: Alias(s):CD1a65535a1:;BLK4:
          PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x0,0xFFFF,0x0)/CDROM(0x1)

     BLK5: Alias(s):
          PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x0,0xFFFF,0x0)/VenMedia(C5BD4D42-1A76-4996-8956-73CDA326CD0A)
     BLK6: Alias(s):
          PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x0,0xFFFF,0x0)/VenMedia(C5BD4D42-1A76-4996-8956-73CDA326CD0A)/CDROM(0x0)
      FS2: Alias(s):CD1a65535ab:;BLK7:
          PciRoot(0x0)/Pci(0x1F,0x2)/Sata(0x0,0xFFFF,0x0)/VenMedia(C5BD4D42-1A76-4996-8956-73CDA326CD0A)/CDROM(0x1)
--- End of mapping table ---

After investigation, I found the UDF logic in Partition driver doesn't truly skip the Eltorito volume.
The code flow is like below:

  1.  <BLK2> is created by ScsiDiskDxe driver.
  2.  By passing <BLK2> to PartitionDxe Start()
     *   <BLK3> and <BLK4/FS1> are created by PartitionDxe driver, by PartitionInstallElToritoChildHandles().
     *   <BLK5> is created by PartitionDxe driver, by PartitionInstallUdfChildHandles().
  3.  By passing <BLK5> to PartitionDxe Start()
     *   <BLK6> and <BLK7/FS2> are created by PartitionDxe driver, by PartitionInstallElToritoChildHandles().

I think step 2.a is not correct if my understanding to UDF is correct. The PartitionInstallUdfChildHandles() should iterate
all volumes in the media and creates the child BLK handle for each volume, but skipping Eltorito volume.

Instead, the current implementation just creates one child BLK handle for the entire media.
To avoid reclusively creating  child BLK handle, the PartitionInstallUdfChildHandles() contains a logic to do nothing when
the handle is created by ParititonDxe driver. The logic is not needed when the implementation follows my suggestion above.
Due to this, step 3.a creates the additional but shouldn't-exist BLK handles <BLK6> and <BLK7/FS2>.

UdfDxe driver is supposed to Start() on each volume and produce SimpleFileSystem protocol.

Do you agree with my above suggestions?

Laszlo,
I understood your needs of this UDF support. But as you can see there are many build failures and even functionality issues due to this support.
I am not sure how the other open source project handles such cases.
But I am thinking maybe we could move the whole UDF support to edk2-staging firstly and move it back after all the issues are resolved.
What's your suggestion?

Thanks/Ray