Re: [PATCH 2/2] MdePkg/UefiGpt.h: Add new definition for enable GPT support

["Chen, Chen A" <chen.a.chen@intel.com>]

-----Original Message-----
From: Wu, Hao A 
Sent: Friday, January 25, 2019 3:27 PM
To: Chen, Chen A <chen.a.chen@intel.com>; Gao, Liming <liming.gao@intel.com>; edk2-devel@lists.01.org
Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Zhang, Chao B <chao.b.zhang@intel.com>
Subject: RE: [edk2] [PATCH 2/2] MdePkg/UefiGpt.h: Add new definition for enable GPT support

> -----Original Message-----
> From: Chen, Chen A
> Sent: Friday, January 25, 2019 3:16 PM
> To: Wu, Hao A; edk2-devel@lists.01.org
> Cc: Kinney, Michael D; Zhang, Chao B; Gao, Liming
> Subject: RE: [edk2] [PATCH 2/2] MdePkg/UefiGpt.h: Add new definition 
> for enable GPT support
> 
> 
> 
> -----Original Message-----
> From: Wu, Hao A
> Sent: Friday, January 25, 2019 11:04 AM
> To: Chen, Chen A <chen.a.chen@intel.com>; edk2-devel@lists.01.org
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Zhang, Chao B 
> <chao.b.zhang@intel.com>; Gao, Liming <liming.gao@intel.com>
> Subject: RE: [edk2] [PATCH 2/2] MdePkg/UefiGpt.h: Add new definition 
> for enable GPT support
> 
> > -----Original Message-----
> > From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf 
> > Of Chen A Chen
> > Sent: Thursday, January 17, 2019 10:03 AM
> > To: edk2-devel@lists.01.org
> > Cc: Kinney, Michael D; Zhang, Chao B; Gao, Liming
> > Subject: [edk2] [PATCH 2/2] MdePkg/UefiGpt.h: Add new definition for 
> > enable GPT support
> >
> > BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1470
> > This two new definitions are defined for GPT in FatPei diver.
> >
> > Cc: Liming Gao <liming.gao@intel.com>
> > Cc: Michael D Kinney <michael.d.kinney@intel.com>
> > Cc: Zhang Chao B <chao.b.zhang@intel.com>
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Chen A Chen <chen.a.chen@intel.com>
> > ---
> >  MdePkg/Include/Uefi/UefiGpt.h | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> > diff --git a/MdePkg/Include/Uefi/UefiGpt.h 
> > b/MdePkg/Include/Uefi/UefiGpt.h index f635b05390..8665c8cbc9 100644
> > --- a/MdePkg/Include/Uefi/UefiGpt.h
> > +++ b/MdePkg/Include/Uefi/UefiGpt.h
> > @@ -24,9 +24,25 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF
> ANY KIND,
> > EITHER EXPRESS OR IMPLIED.
> >  /// EFI Partition Table Signature: "EFI PART".
> >  ///
> >  #define EFI_PTAB_HEADER_ID      SIGNATURE_64 ('E','F','I',' ','P','A','R','T')
> > +///
> > +/// Minimum bytes reserve for EFI entry array buffer.
> > +///
> > +#define GPT_PART_ENTRY_MIN_SIZE 16384
> 
> May I know where this definition comes from?
> Does it come from the UEFI spec?
> 
> Chen: The MACRO is not explicitly defined in UEFI Spec, But UEFI Spec 
> specifies a minimum value for GPT entry araray.

Does it comes from the below content within the UEFI spec?

> A minimum of 16,384 bytes of space must be reserved for the GPT 
> Partition Entry Array.

If so, I am not sure whether 'EFI_' prefix should be added before 'GPT_PART_ENTRY_MIN_SIZE'.

Liming, could you help to confirm?

Chen: I have no strong opinion on ' GPT_PART_ENTRY_MIN_SIZE' and 'EFI_GPT_PART_ENTRY_MIN_SIZE'. 

> 
> >
> >  #pragma pack(1)
> >
> > +///
> > +/// MBR Partition Entry
> > +///
> > +typedef struct {
> > +  UINT8   BootIndicator;
> > +  UINT8   StartingCHS[3];
> > +  UINT8   OSType;
> > +  UINT8   EndingCHS[3];
> > +  UINT32  StartingLBA;
> > +  UINT32  SizeInLBA;
> > +} MBR_PARTITION_ENTRY;
> > +
> 
> What about using the 'MBR_PARTITION_RECORD' definition within 
> edk2/MdePkg/Include/IndustryStandard/Mbr.h
> 
> and thus get rid of adding this one?
> 
> Chen: This structure defined as the following format in Mbr.h
> 
> typedef struct {
>   ..
>   UINT8 StartingLBA[4];
>   UINT8 SizeInLBA[4];
> } MBR_PARTITION_RECORD;
> 
> For StartingLBA, this field is represented the LBA, so I think it 
> should be
> UINT32 type not an array type.

I do not get your point, what prevents you from getting the LBA information for the byte array?

Chen: Yes, GPT DXE driver use UNPACK_UINT32 macro to extract UINT32	from array. But I thought use UINT32 type get the value more directly.

Best Regards,
Hao Wu

> 
> The same meaning is also for SizeInLba.
> 
> Best Regards,
> Hao Wu
> 
> >  ///
> >  /// GPT Partition Table Header.
> >  ///
> > --
> > 2.16.2.windows.1
> >
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