linux-kernel - Re: [PATCH v3 1/3] dyndbg: make dyndbg a known cli param

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Date:   Wed, 22 Sep 2021 12:23:16 -0600
From:   jim.cromie@...il.com
To:     Andrew Halaney <ahalaney@...hat.com>
Cc:     Jason Baron <jbaron@...mai.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] dyndbg: make dyndbg a known cli param

On Mon, Sep 20, 2021 at 2:55 PM Andrew Halaney <ahalaney@...hat.com> wrote:
>
> Right now dyndbg shows up as an unknown parameter if used on boot:
>
>     Unknown command line parameters: dyndbg=+p
>
> That's because it is unknown, it doesn't sit in the __param
> section, so the processing done to warn users supplying an unknown
> parameter doesn't think it is legitimate.
>
> Install a dummy handler to register it. dynamic debug needs to search
> the whole command line for modules listed that are currently builtin,
> so there's no real work to be done in this callback.
>
> Fixes: 86d1919a4fb0 ("init: print out unknown kernel parameters")
> Signed-off-by: Andrew Halaney <ahalaney@...hat.com>


I just validated that this does NOT block or short circuit  bare
dyndbg=  processing,

[    0.981166] dyndbg: dyndbg="+fl"
[    0.981281] dyndbg: query 0: "+fl"
[    0.981836] dyndbg: split into words: "+fl"
[    0.982281] dyndbg: op='+'
[    0.982861] dyndbg: flags=0xc
[    0.983281] dyndbg: *flagsp=0xc *maskp=0xffffffff
[    0.984044] dyndbg: parsed: func="" file="" module="" format="" lineno=0-0
[    0.984298] dyndbg: changed arch/x86/pci/irq.c:1312
[irq]pcibios_fixup_irqs =fl
[    0.985284] dyndbg: changed arch/x86/pci/irq.c:1259
[irq]pcibios_lookup_irq =fl
[    0.986281] dyndbg: changed arch/x86/pci/irq.c:1229
[irq]pcibios_lookup_irq =fl

you have my T-B

> ---
>  lib/dynamic_debug.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
> index cb5abb42c16a..84c16309cc63 100644
> --- a/lib/dynamic_debug.c
> +++ b/lib/dynamic_debug.c
> @@ -761,6 +761,18 @@ static __init int ddebug_setup_query(char *str)
>
>  __setup("ddebug_query=", ddebug_setup_query);
>
> +/*
> + * Install a noop handler to make dyndbg look like a normal kernel cli param.
> + * This avoids warnings about dyndbg being an unknown cli param when supplied
> + * by a user.
> + */
> +static __init int dyndbg_setup(char *str)
> +{
> +       return 1;
> +}
> +
> +__setup("dyndbg=", dyndbg_setup);
> +
>  /*
>   * File_ops->write method for <debugfs>/dynamic_debug/control.  Gathers the
>   * command text from userspace, parses and executes it.
> --
> 2.31.1
>