linux-kernel - Re: [PATCH] efistub: add efi=quiet parameter to selectively silence efistub alone

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Message-ID: <CAMj1kXEeJattXAkvitfyu3KRRokkSMJZR0xgg_+DG2Mk-tMuoA@mail.gmail.com>
Date: Mon, 20 Jan 2025 09:45:29 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: "Hendrik 'T4cC0re' Meyer" <linux@....dev>
Cc: linux-doc@...r.kernel.org, linux-efi@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efistub: add efi=quiet parameter to selectively silence
 efistub alone

On Sun, 19 Jan 2025 at 18:32, Hendrik 'T4cC0re' Meyer <linux@....dev> wrote:
>
> Hello!
>
> > Could you explain the use case please? Your concern is that removing
> 'quiet' from the command line is producing a few additional lines of
> output from the EFI stub at boot?
>
> Sure :) I boot a UKI (with Secure Boot and TPM measurements)  with an
> embedded splash image, and the cmdline
> 'memtest=2 earlyprintk=serial,ttyS0,115200 console=ttyS0,115200n8'
>
> The stub by default (without 'quiet') will print messages regarding
> the UKI and it being measured into the TPM on the efifb (I assume)
> rendering on top of the displayed splash image.
>
> "EFI stub: Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path"
>  and "EFI stub: Measured initrd data into PCR 9" to be specific.
>
> > How is that a problem compared to
> the fact that you get the entire kernel log printed to the console?
>
> Very relevant question. Because of the 'memtest=2' flag, there is a
> delay during boot, which should be logged (with memtest progress) to
> the serial console. 'quiet' will silence these logs.
>
> > Is every single line printed there relevant to you, and only the ones
> emitted by the EFI stub are not?
>
> Basically, yes. I want the kernel's printk's, but not have the output
> of the efistub dipsplayed on top of the splash screen of the UKI.
>
> I did not find a way to redirect this output, and adding a 'efi=quiet'
> option seemed like a low hanging fruit.
>

I'd prefer to just raise the verbosity level of those messages instead.