Re: [PATCH V2 3/3] DuetPkg FsVariable: Update GetNextVariableName to follow UEFI 2.7

["Zeng, Star" <star.zeng@intel.com>]

It is to return EFI_INVALID_PARAMETER when the input VariableName and VendorGuid are not a valid variable to search next variable.
It is added from UEFI 2.7 spec.
Before the spec change, the code is to return EFI_NOT_FOUND at that case.
After the spec change, EFI_NOT_FOUND seemingly is reserved to indicate the ending of searching.


Thanks,
Star
-----Original Message-----
From: Ni, Ruiyu 
Sent: Monday, June 26, 2017 1:37 PM
To: Zeng, Star <star.zeng@intel.com>; edk2-devel@lists.01.org
Cc: Gao, Liming <liming.gao@intel.com>
Subject: RE: [PATCH V2 3/3] DuetPkg FsVariable: Update GetNextVariableName to follow UEFI 2.7

I understand your point.
But I do think it hurts readability.

BTW, what does the below change does?
   if (Variable.CurrPtr == NULL || EFI_ERROR (Status)) {
+    if (VariableName[0] != 0) {
+      //
+      // The input values of VariableName and VendorGuid are not a name and GUID of an existing variable.
+      //
+      Status = EFI_INVALID_PARAMETER;
+    }
     return Status;
   }


Thanks/Ray

> -----Original Message-----
> From: Zeng, Star
> Sent: Monday, June 26, 2017 11:05 AM
> To: Ni, Ruiyu <ruiyu.ni@intel.com>; edk2-devel@lists.01.org
> Cc: Gao, Liming <liming.gao@intel.com>; Zeng, Star 
> <star.zeng@intel.com>
> Subject: RE: [PATCH V2 3/3] DuetPkg FsVariable: Update 
> GetNextVariableName to follow UEFI 2.7
> 
> Ray,
> 
> The code is like low hanging fruit from my practice for me, and I 
> don't think it hurts readability although it may not bring performance 
> improvement, it depends on how many variables in variable region, how 
> many times of calling GetNextVariableName, and how fast of GetNextVariableName.
> 
> The code practice I did is on NT32 and my real platforms. Is there 
> anyone can make sure he/she tested all the systems in the world for their code?
> 
> 
> Anyway, I can update the patch if you insist.
> 
> 
> Thanks,
> Star
> -----Original Message-----
> From: Ni, Ruiyu
> Sent: Saturday, June 24, 2017 10:08 AM
> To: Zeng, Star <star.zeng@intel.com>; edk2-devel@lists.01.org
> Cc: Gao, Liming <liming.gao@intel.com>
> Subject: RE: [PATCH V2 3/3] DuetPkg FsVariable: Update 
> GetNextVariableName to follow UEFI 2.7
> 
> Star,
> I don't recommend to add the additional check for performance 
> consideration.
> Because we have no idea what the input VariableName buffer is like.
> If the VariableName is like ['\0', '?', '?', '?'] with MaxLen equals 
> to 4, "VariableName[MaxLen-1] != 0" check is redundant.
> The NT32 case you met cannot represent the all possible cases.
> You could use the possibility theory to decide what the most efficient way is.
> 
> Additionally I think code readability is more important than efficiency.
> In this case, we need the data about the performance improvement to 
> decide whether this check is necessary.
> 
> 
> Regards,
> Ray
> 
> >-----Original Message-----
> >From: Zeng, Star
> >Sent: Friday, June 23, 2017 5:33 PM
> >To: Ni, Ruiyu <ruiyu.ni@intel.com>; edk2-devel@lists.01.org
> >Cc: Gao, Liming <liming.gao@intel.com>; Zeng, Star 
> ><star.zeng@intel.com>
> >Subject: RE: [PATCH V2 3/3] DuetPkg FsVariable: Update 
> >GetNextVariableName to follow UEFI 2.7
> >
> >Ray,
> >
> >It is to pass the check quickly and avoid scanning all the chars in 
> >VariableName by StrnLenS for normal boot without invalid cases.
> >I did experiments in the code of GetNextVariableName with below debug 
> >code for normal boot on NT32 and my real platforms, all the cases 
> >will go
> into the branch "xxx 2".
> >  if (((VariableName[MaxLen - 1] != 0))) {
> >    DEBUG ((DEBUG_INFO, "xxx 1\n"));
> >  } else {
> >    DEBUG ((DEBUG_INFO, "xxx 2\n"));
> >  }
> >
> >
> >Thanks,
> >Star
> >-----Original Message-----
> >From: Ni, Ruiyu
> >Sent: Friday, June 23, 2017 4:20 PM
> >To: Zeng, Star <star.zeng@intel.com>; edk2-devel@lists.01.org
> >Cc: Gao, Liming <liming.gao@intel.com>
> >Subject: RE: [PATCH V2 3/3] DuetPkg FsVariable: Update 
> >GetNextVariableName to follow UEFI 2.7
> >
> >Star,
> >What's the benefit of this check "VariableName[MaxLen - 1] != 0"?
> >I think this check "StrnLenS (VariableName, MaxLen) == MaxLen" should 
> >be
> enough.
> >
> >Thanks/Ray
> >
> >> -----Original Message-----
> >> From: Zeng, Star
> >> Sent: Friday, June 23, 2017 4:08 PM
> >> To: edk2-devel@lists.01.org
> >> Cc: Zeng, Star <star.zeng@intel.com>; Gao, Liming 
> >> <liming.gao@intel.com>; Ni, Ruiyu <ruiyu.ni@intel.com>
> >> Subject: [PATCH V2 3/3] DuetPkg FsVariable: Update 
> >> GetNextVariableName to follow UEFI 2.7
> >>
> >> "The size must be large enough to fit input string supplied in 
> >> VariableName buffer" is added in the description for VariableNameSize.
> >> And two cases of EFI_INVALID_PARAMETER are added.
> >> 1. The input values of VariableName and VendorGuid are not a name and
> >>    GUID of an existing variable.
> >> 2. Null-terminator is not found in the first VariableNameSize bytes of
> >>    the input VariableName buffer.
> >>
> >> This patch is to update code to follow them.
> >>
> >> Cc: Liming Gao <liming.gao@intel.com>
> >> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> >> Contributed-under: TianoCore Contribution Agreement 1.0
> >> Signed-off-by: Star Zeng <star.zeng@intel.com>
> >> ---
> >>  DuetPkg/FSVariable/FSVariable.c | 21 ++++++++++++++++++++-
> >>  1 file changed, 20 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/DuetPkg/FSVariable/FSVariable.c 
> >> b/DuetPkg/FSVariable/FSVariable.c index 34b79305c871..6069cfa8fb98
> >> 100644
> >> --- a/DuetPkg/FSVariable/FSVariable.c
> >> +++ b/DuetPkg/FSVariable/FSVariable.c
> >> @@ -6,7 +6,7 @@ disk. They can be changed by user. BIOS is not able 
> >> to protoect those.
> >>  Duet trusts all meta data from disk. If variable code, variable 
> >> metadata and variable  data is modified in inproper way, the 
> >> behavior is undefined.
> >>
> >> -Copyright (c) 2006 - 2016, Intel Corporation. All rights 
> >> reserved.<BR>
> >> +Copyright (c) 2006 - 2017, Intel Corporation. All rights 
> >> +reserved.<BR>
> >>  This program and the accompanying materials  are licensed and made 
> >> available under the terms and conditions of the BSD License  which 
> >> accompanies this distribution.  The full text of the license may be 
> >> found at @@ -1400,14 +1400,33 @@ Returns:
> >>    VARIABLE_POINTER_TRACK  Variable;
> >>    UINTN                   VarNameSize;
> >>    EFI_STATUS              Status;
> >> +  UINTN                   MaxLen;
> >>
> >>    if (VariableNameSize == NULL || VariableName == NULL || 
> >> VendorGuid ==
> >> NULL) {
> >>      return EFI_INVALID_PARAMETER;
> >>    }
> >>
> >> +  //
> >> +  // Calculate the possible maximum length of name string, 
> >> + including the Null
> >> terminator.
> >> +  //
> >> +  MaxLen = *VariableNameSize / sizeof (CHAR16);  if ((MaxLen == 0)
> >> + ||
> >> +      ((VariableName[MaxLen - 1] != 0) && (StrnLenS (VariableName,
> >> + MaxLen)
> >> == MaxLen))) {
> >> +    //
> >> +    // Null-terminator is not found in the first VariableNameSize 
> >> + bytes of the
> >> input VariableName buffer.
> >> +    //
> >> +    return EFI_INVALID_PARAMETER;
> >> +  }
> >> +
> >>    Status = FindVariable (VariableName, VendorGuid, &Variable);
> >>
> >>    if (Variable.CurrPtr == NULL || EFI_ERROR (Status)) {
> >> +    if (VariableName[0] != 0) {
> >> +      //
> >> +      // The input values of VariableName and VendorGuid are not a 
> >> + name
> >> and GUID of an existing variable.
> >> +      //
> >> +      Status = EFI_INVALID_PARAMETER;
> >> +    }
> >>      return Status;
> >>    }
> >>
> >> --
> >> 2.7.0.windows.1