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

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Message-ID: <5800c426-95fd-4a81-b979-c0bc2bc293dd@kernel.org>
Date: Wed, 9 Jul 2025 16:39:49 +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 16:31, 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?

Best regards,
Krzysztof