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

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

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