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

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Message-ID: <4cix3k4h32wozt3nxic5un7jyzfjrmqmzbzmtr3ivw5b2bz363@mw6bke7w4oaq>
Date: Wed, 9 Jul 2025 16:31:57 +0200
From: Gerd Hoffmann <kraxel@...hat.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
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 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.

In case the firmware does not have a log buffer the
sysfs file is not present.

take care,
  Gerd