Re: [PATCH 1/7] OvmfPkg: introduce QemuFwCfgSimpleParserLib

["Laszlo Ersek" <lersek@redhat.com>]

On 04/24/20 11:13, Philippe Mathieu-Daudé wrote:
> On 4/24/20 9:53 AM, Laszlo Ersek wrote:
>> We already parse some boolean and integer values from named fw_cfg files
>> (usually into PCDs), and we're going to cover more. Add a dedicated
>> library for centralizing the parsing logic.
>>
>> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Cc: Per Sundstrom <per_sundstrom@yahoo.com>
>> Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
>> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2681
>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
>> ---
>>  
>> OvmfPkg/OvmfPkg.dec                                                  
>> |   4 +
>>  
>> OvmfPkg/OvmfPkgIa32.dsc                                              
>> |   1 +
>>  
>> OvmfPkg/OvmfPkgIa32X64.dsc                                           
>> |   1 +
>>  
>> OvmfPkg/OvmfPkgX64.dsc                                               
>> |   1 +
>>  
>> OvmfPkg/Include/Library/QemuFwCfgSimpleParserLib.h                   
>> | 128 +++++++
>>  
>> OvmfPkg/Library/QemuFwCfgSimpleParserLib/QemuFwCfgSimpleParserLib.inf
>> |  27 ++
>>  
>> OvmfPkg/Library/QemuFwCfgSimpleParserLib/QemuFwCfgSimpleParser.c     
>> | 398 ++++++++++++++++++++
>>   7 files changed, 560 insertions(+)
>>
>> diff --git a/OvmfPkg/OvmfPkg.dec b/OvmfPkg/OvmfPkg.dec
>> index 28030391cff2..8a46fe73344e 100644
>> --- a/OvmfPkg/OvmfPkg.dec
>> +++ b/OvmfPkg/OvmfPkg.dec
>> @@ -60,6 +60,10 @@ [LibraryClasses]
>>     #
>>     QemuFwCfgS3Lib|Include/Library/QemuFwCfgS3Lib.h
>>   +  ##  @libraryclass  Parse the contents of named fw_cfg files as
>> simple
>> +  #                  (scalar) data types.
>> +  QemuFwCfgSimpleParserLib|Include/Library/QemuFwCfgSimpleParserLib.h
>> +
>>     ##  @libraryclass  Rewrite the BootOrder NvVar based on QEMU's
>> "bootorder"
>>     #                  fw_cfg file.
>>     #
>> diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
>> index d5e90c001370..5e2972063110 100644
>> --- a/OvmfPkg/OvmfPkgIa32.dsc
>> +++ b/OvmfPkg/OvmfPkgIa32.dsc
>> @@ -160,6 +160,7 @@ [LibraryClasses]
>>     UefiUsbLib|MdePkg/Library/UefiUsbLib/UefiUsbLib.inf
>>    
>> SerializeVariablesLib|OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.inf
>>
>>     QemuFwCfgLib|OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgDxeLib.inf
>> + 
>> QemuFwCfgSimpleParserLib|OvmfPkg/Library/QemuFwCfgSimpleParserLib/QemuFwCfgSimpleParserLib.inf
>>
>>     VirtioLib|OvmfPkg/Library/VirtioLib/VirtioLib.inf
>>     LoadLinuxLib|OvmfPkg/Library/LoadLinuxLib/LoadLinuxLib.inf
>>    
>> MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf
>>
>> diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
>> index 066f49aeaee0..18e6909a33fa 100644
>> --- a/OvmfPkg/OvmfPkgIa32X64.dsc
>> +++ b/OvmfPkg/OvmfPkgIa32X64.dsc
>> @@ -164,6 +164,7 @@ [LibraryClasses]
>>     UefiUsbLib|MdePkg/Library/UefiUsbLib/UefiUsbLib.inf
>>    
>> SerializeVariablesLib|OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.inf
>>
>>     QemuFwCfgLib|OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgDxeLib.inf
>> + 
>> QemuFwCfgSimpleParserLib|OvmfPkg/Library/QemuFwCfgSimpleParserLib/QemuFwCfgSimpleParserLib.inf
>>
>>     VirtioLib|OvmfPkg/Library/VirtioLib/VirtioLib.inf
>>     LoadLinuxLib|OvmfPkg/Library/LoadLinuxLib/LoadLinuxLib.inf
>>    
>> MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf
>>
>> diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
>> index ac510522a9ff..3d24cc4c1cfb 100644
>> --- a/OvmfPkg/OvmfPkgX64.dsc
>> +++ b/OvmfPkg/OvmfPkgX64.dsc
>> @@ -164,6 +164,7 @@ [LibraryClasses]
>>     UefiUsbLib|MdePkg/Library/UefiUsbLib/UefiUsbLib.inf
>>    
>> SerializeVariablesLib|OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.inf
>>
>>     QemuFwCfgLib|OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgDxeLib.inf
>> + 
>> QemuFwCfgSimpleParserLib|OvmfPkg/Library/QemuFwCfgSimpleParserLib/QemuFwCfgSimpleParserLib.inf
>>
>>     VirtioLib|OvmfPkg/Library/VirtioLib/VirtioLib.inf
>>     LoadLinuxLib|OvmfPkg/Library/LoadLinuxLib/LoadLinuxLib.inf
>>    
>> MemEncryptSevLib|OvmfPkg/Library/BaseMemEncryptSevLib/BaseMemEncryptSevLib.inf
>>
>> diff --git a/OvmfPkg/Include/Library/QemuFwCfgSimpleParserLib.h
>> b/OvmfPkg/Include/Library/QemuFwCfgSimpleParserLib.h
>> new file mode 100644
>> index 000000000000..c6062bae8770
>> --- /dev/null
>> +++ b/OvmfPkg/Include/Library/QemuFwCfgSimpleParserLib.h
>> @@ -0,0 +1,128 @@
>> +/** @file
>> +  Parse the contents of named fw_cfg files as simple (scalar) data
>> types.
>> +
>> +  Copyright (C) 2020, Red Hat, Inc.
>> +
>> +  SPDX-License-Identifier: BSD-2-Clause-Patent
>> +**/
>> +
>> +#ifndef QEMU_FW_CFG_SIMPLE_PARSER_LIB_H_
>> +#define QEMU_FW_CFG_SIMPLE_PARSER_LIB_H_
>> +
>> +#include <Base.h>
>> +
>> +/**
>> +  Look up FileName with QemuFwCfgFindFile() from QemuFwCfgLib. Read
>> the fw_cfg
>> +  file into a small array with automatic storage duration. Parse the
>> array as
>> +  the textual representation of a BOOLEAN.
>> +
>> +  @param[in] FileName  The name of the fw_cfg file to look up and parse.
>> +
>> +  @param[out] Value    On success, Value is TRUE if the contents of
>> the fw_cfg
>> +                       file case-insensitively match "true", "yes", "y",
>> +                       "enable", "enabled", "1".
>> +
>> +                       On success, Value is FALSE if the contents of
>> the fw_cfg
>> +                       file case-insensitively match "false", "no", "n",
>> +                       "disable", "disabled", "0".
>> +
>> +                       On failure, Value is not changed.
>> +
>> +  @retval RETURN_SUCCESS         Parsing successful. Value has been set.
>> +
>> +  @retval RETURN_UNSUPPORTED     Firmware configuration is unavailable.
>> +
>> +  @retval RETURN_PROTOCOL_ERROR  Parsing failed. Value has not been
>> changed.
>> +
>> +  @return                        Error codes propagated from
>> +                                 QemuFwCfgFindFile(). Value has not been
>> +                                 changed.
>> +**/
>> +RETURN_STATUS
>> +EFIAPI
>> +QemuFwCfgParseBool (
>> +  IN  CONST CHAR8 *FileName,
>> +  OUT BOOLEAN     *Value
>> +  );
>> +
>> +/**
>> +  Look up FileName with QemuFwCfgFindFile() from QemuFwCfgLib. Read
>> the fw_cfg
>> +  file into a small array with automatic storage duration. Parse the
>> array as
>> +  the textual representation of a UINT8.
>> +
>> +  @param[in] FileName    The name of the fw_cfg file to look up and
>> parse.
>> +
>> +  @param[in] ParseAsHex  If TRUE, call BaseLib's
>> AsciiStrHexToUint64S() for
>> +                         parsing the fw_cfg file.
>> +
>> +                         If FALSE, call BaseLib's
>> AsciiStrDecimalToUint64S()
>> +                         for parsing the fw_cfg file.
>> +
>> +  @param[out] Value      On success, Value has been parsed with the
>> BaseLib
>> +                         function determined by ParseAsHex, and also
>> +                         range-checked for [0, MAX_UINT8].
>> +
>> +                         On failure, Value is not changed.
>> +
>> +  @retval RETURN_SUCCESS         Parsing successful. Value has been set.
>> +
>> +  @retval RETURN_UNSUPPORTED     Firmware configuration is unavailable.
>> +
>> +  @retval RETURN_PROTOCOL_ERROR  Parsing failed. Value has not been
>> changed.
>> +
>> +  @retval RETURN_PROTOCOL_ERROR  Parsing succeeded, but the result
>> does not fit
>> +                                 in the [0, MAX_UINT8] range. Value
>> has not
>> +                                 been changed.
> 
> I wondered about RETURN_BAD_BUFFER_SIZE / RETURN_BUFFER_TOO_SMALL for
> this case, but RETURN_PROTOCOL_ERROR is less confusing.

Right. I too considered the ...BUFFER... error codes first. I opted for
"protocol error" instead because the ...BUFFER... codes "blame the
caller", or at least inform the caller to repeat the call with a more
appropriately sized buffer (or integer range).

But in this case, the caller knows best, by design. So "bad buffer size"
is actually a QEMU misconfiguration / information exchange error (hence
"protocol error") between QEMU and firmware. The caller (in edk2) is not
supposed to retry with a differently sized buffer (or integer range).

[...]

> Neat.
> Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
> 

Thanks!
Laszlo