linux-kernel - Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline

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Date:	Mon, 05 May 2014 06:15:02 -0700
From:	Randy Dunlap <rdunlap@...radead.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mateusz Guzik <mguzik@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Ingo Molnar <mingo@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Kay Sievers <kay@...y.org>
Subject: Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline

On 05/04/2014 07:17 PM, Rusty Russell wrote:
> Andrew Morton <akpm@...ux-foundation.org> writes:
>> On Mon, 07 Apr 2014 14:24:45 +0930 Rusty Russell <rusty@...tcorp.com.au> wrote:
>>
>>> Subject: param: hand arguments after -- straight to init
>>>
>>> The kernel passes any args it doesn't need through to init, except it
>>> assumes anything containing '.' belongs to the kernel (for a module).
>>> This change means all users can clearly distinguish which arguments
>>> are for init.
>>>
>>> For example, the kernel uses debug ("dee-bug") to mean log everything to
>>> the console, where systemd uses the debug from the Scandinavian "day-boog"
>>> meaning "fail to boot".  If a future versions uses argv[] instead of
>>> reading /proc/cmdline, this confusion will be avoided.
>>>
>>> eg: test 'FOO="this is --foo"' -- 'systemd.debug="true true true"'
>>>
>>> Gives:
>>> argv[0] = '/debug-init'
>>> argv[1] = 'test'
>>> argv[2] = 'systemd.debug=true true true'
>>> envp[0] = 'HOME=/'
>>> envp[1] = 'TERM=linux'
>>> envp[2] = 'FOO=this is --foo'
>>
>> This (user-facing) feature doesn't seem to have been documented
>> anywhere.  Documentation/kernel-parameters.txt, I guess.
>
> That document does need some love.  How's this?
>
> 1) __setup() is messy, prefer module_param and core_param.
> 2) Document --
> 3) Document modprobe scraping /proc/cmdline.
> 4) Document handing of leftover parameters to init.
> 5) Document use of quotes to protect whitespace.
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 43842177b771..56a4c2d0c741 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1,27 +1,37 @@
>                             Kernel Parameters
>                             ~~~~~~~~~~~~~~~~~
>
> -The following is a consolidated list of the kernel parameters as implemented
> -(mostly) by the __setup() macro and sorted into English Dictionary order
> -(defined as ignoring all punctuation and sorting digits before letters in a
> -case insensitive manner), and with descriptions where known.
> -
> -Module parameters for loadable modules are specified only as the
> -parameter name with optional '=' and value as appropriate, such as:
> -
> -	modprobe usbcore blinkenlights=1
> -
> -Module parameters for modules that are built into the kernel image
> -are specified on the kernel command line with the module name plus
> -'.' plus parameter name, with '=' and value if appropriate, such as:
> -
> -	usbcore.blinkenlights=1
> +The following is a consolidated list of the kernel parameters as
> +implemented by the __setup(), core_param() and module_param() macros
> +and sorted into English Dictionary order (defined as ignoring all
> +punctuation and sorting digits before letters in a case insensitive
> +manner), and with descriptions where known.
> +
> +The kernel parses parameters from the kernel command line up to "--";
> +if it doesn't recognize a parameter and it doesn't contain a '.', the
> +parameter gets passed to init: parameters with '=' go into init's
> +environment, others are passed as command line arguments to init.
> +Everything after "--" is passed as an argument to init.
> +
> +Module parameters can be specified in two ways: via the kernel command
> +line with a module name prefix, or via modprobe, eg:

All looks good to me except for 2 instances of "eg" which should be
"e.g." (just above and about 4 paragraphs below here).

> +
> +	(kernel command line) usbcore.blinkenlights=1
> +	(modprobe command line) modprobe usbcore blinkenlights=1
> +
> +Parameters for modules which are built into the kernel need to be
> +specified on the kernel command line.  modprobe looks through the
> +kernel command line (/proc/cmdline) and collects module parameters
> +when it loads a module, so the kernel command line can be used for
> +loadable modules too.
>
>   Hyphens (dashes) and underscores are equivalent in parameter names, so
>   	log_buf_len=1M print-fatal-signals=1
>   can also be entered as
>   	log-buf-len=1M print_fatal_signals=1
>
> +Double-quotes can be used to protect spaces in values, eg:
> +	param="spaces in here"
>
>   This document may not be entirely up to date and comprehensive. The command
>   "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
> --


-- 
~Randy
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