Re: [edk2-devel] [PATCH V1 1/1] OvmfPkg/QemuBootOrderLib: Measure the etc/boot-menu-wait

["sunceping" <cepingx.sun@intel.com>]

On Thursday, March 14, 2024 5:31 PM Gerd Hoffmann wrote:
> Load, measure and cache all fw_cfg entries we care about early in the PEI phase
> (or SEC phase for pei-less builds), so we can
>  (a) easily have a fixed order, and
>  (b) store them all in HOBs?
> 
> Which implies SEC/PEI must read all relevant fw_cfg entries, even in case they
> are used only later in the DXE phase.
> 
> Advantage is we have a single cache which can be used in all firmware phases.
> When using global variables in DXE we still can end up reading entries multiple
> times, either because entries are needed by both PEI and DXE, or because
> multiple DXE modules need them (global variables are per module).
> 
We have some concerns that in above solution the size of a single cache is large
( because all fw_cfg data need to be read from qemu). 
Further more this is not a lazy mode which means some fw_cfg data 
may be read but it is not to be consumed later. 

We propose below solution :

Add a new API in QemuFwCfgLib,
RETURN_STATUS QemuFwCfgGetData(fw_cfg_name, *size, *value, FW_CFG_GET_DATA_FLAG flag).	

Input:
@fw_cfg_name: The fw_cfg file name .
@size: Number of bytes in the file.
@value: Value of fw_cfg item read. 
@flag: Bitmap providing additional information(cache?  measurement ?)
             #define  FW_CFG_GET_DATA_CACHE 0x00000001
             #define  FW_CFG_GET_DATA_MEASUREMENT 0x00000002

Output:
@return: RETURN_NOT_FOUND: The fw_cfg file is not found
	   RETURN_UNSUPPORTED: The fw_cfg is unavailable.
                 RETURN_BUFFER_TOO_SMALL: The required buffer size is in @size.
                 RETURN_SUCCESS:  The fw_cfg file is found and load the data successfully.

Description:
 This function finds fw_cfg item and reads its data into value.  And it also provides callers with
 options to cache and/or measurement. 

Pros:
Caller can decide how to get the fw_cfg data from QEMU (cache? Measurement?)
 And it can reduce the code complexity because it pack 3 fw_cfg call 
(QemuFwCfgFindFile/QemuFwCfgSelectItem/QemuFwCfgReadBytes) into one call. 

What's your thought?


Thanks
Ceping


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