linux-kernel - Re: [PATCH] bootup: Add built-in kernel command line for x86

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Date:	Mon, 11 Aug 2008 15:40:35 -0700
From:	Tim Bird <tim.bird@...sony.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	linux kernel <linux-kernel@...r.kernel.org>,
	linux-embedded <linux-embedded@...r.kernel.org>,
	Matt Mackall <mpm@...enic.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] bootup: Add built-in kernel command line for x86

H. Peter Anvin wrote:
> Ingo Molnar wrote:
>> * Tim Bird <tim.bird@...sony.com> wrote:
>>
>>> Add support for a built-in command line for x86 architectures. The
>>> Kconfig help gives the major rationale for this addition.
>>
>> i have actually used a local hack quite similar to this to inject boot
>> options into bzImages via randconfig - so i would find this feature
>> rather useful.
>>
>> a small observation:
>>
>>> +    /* append boot loader cmdline to builtin, unless builtin
>>> overrides it */
>>> +    if (builtin_cmdline[0] != '!') {
>>> +        strlcat(builtin_cmdline, " ", COMMAND_LINE_SIZE);
>>> +        strlcat(builtin_cmdline, boot_command_line, COMMAND_LINE_SIZE);
>>> +        strlcpy(boot_command_line, builtin_cmdline, COMMAND_LINE_SIZE);
>>> +    } else {
>>> +        strlcpy(boot_command_line, &builtin_cmdline[1],
>>> +            COMMAND_LINE_SIZE);
>>> +    }
>>
>> the default branch changes existing command lines slightly: it appends
>> a space to them. This could break scripts that rely on the precise
>> contents of /proc/cmdline output. (i have some - they are arguably dodgy)

Yeah, I wasn't too comfortable with that.

>> Best would be to make it really apparent in the code that nothing
>> changes if this config option is not set. Preferably there should be
>> no extra code at all in that case.

Agreed.

> 
> I would like to see this:
> 
> #ifdef CONFIG_BUILTIN_CMDLINE
> # ifdef CONFIG_BUILTIN_CMDLINE_OVERRIDE
>     strlcpy(boot_command_line, builtin_cmdline, COMMAND_LINE_SIZE);
> # else
>     if (boot_command_line) {
>         strlcat(builtin_cmdline, " ", COMMAND_LINE_SIZE);
>         strlcat(builtin_cmdline, boot_command_line, COMMAND_LINE_SIZE);
>     }
> # endif
> #endif

You missed copying builtin_cmdline back to boot_command_line, but
in general this looks OK to me.  If nobody objects to the ifdef
multiplicity, I'll work up a version tomorrow for review.  (Sorry,
I'm a bit swamped today.)
 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
=============================

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