linux-kernel - Re: [PATCH v2] efi: add ovmf debug log driver

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Message-ID: <73a18fe6-daef-4035-abb2-67db2c5619e2@kernel.org>
Date: Wed, 9 Jul 2025 16:40:35 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Gerd Hoffmann <kraxel@...hat.com>
Cc: linux-efi@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] efi: add ovmf debug log driver

On 09/07/2025 16:39, Krzysztof Kozlowski wrote:
> On 09/07/2025 16:31, Gerd Hoffmann wrote:
>> On Wed, Jul 09, 2025 at 04:20:49PM +0200, Krzysztof Kozlowski wrote:
>>> On 09/07/2025 16:17, Gerd Hoffmann wrote:
>>>> On Wed, Jul 09, 2025 at 03:58:58PM +0200, Krzysztof Kozlowski wrote:
>>>>> On 08/07/2025 14:56, Gerd Hoffmann wrote:
>>>>>> +MODULE_DESCRIPTION("OVMF debug log");
>>>>>> +MODULE_AUTHOR("Gerd Hoffmann <kraxel@...hat.com>");
>>>>>> +MODULE_LICENSE("GPL");
>>>>>> +MODULE_ALIAS("platform:ovmf_debug_log");
>>>>>> diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
>>>>>> index db8c5c03d3a2..ac0a03ec3452 100644
>>>>>> --- a/drivers/firmware/efi/Kconfig
>>>>>> +++ b/drivers/firmware/efi/Kconfig
>>>>>> @@ -263,6 +263,14 @@ config EFI_COCO_SECRET
>>>>>>  	  virt/coco/efi_secret module to access the secrets, which in turn
>>>>>>  	  allows userspace programs to access the injected secrets.
>>>>>>  
>>>>>> +config OVMF_DEBUG_LOG
>>>>>> +	tristate "Expose OVMF firmware debug log via sysfs"
>>>>>> +	depends on EFI
>>>>>> +	help
>>>>>> +	  Recent OVMF versions (edk2-stable202508 + newer) can write
>>>>>> +	  their debug log to a memory buffer.  This driver exposes the
>>>>>> +	  log content via sysfs (/sys/firmware/efi/ovmf_debug_log).
>>>>>
>>>>> Where did you document new ABI?
>>>>
>>>> The log buffer header struct is documented in the header file for the
>>>> edk2 code:
>>>> https://github.com/tianocore/edk2/blob/master/OvmfPkg/Include/Library/MemDebugLogLib.h
>>>
>>> You added a new sysfs interface. I meant documentation for this.
>>
>> The sysfs file contains the log and you can simply use
>> 'cat /sys/firmware/efi/ovmf_debug_log' to read it.
> 
> Don't explain how it works to me. I did not ask how it works. I asked
> where is the new ABI documented?
... and if answer is nowhere, then that's the problem. You need to
document new ABI - see docs in kernel sources.

Best regards,
Krzysztof