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

Rusty Russell
2014-05-05T02:20:06Z

Andrew Morton <akpm@linux-foundation.org> writes:
> On Mon, 07 Apr 2014 14:24:45 +0930 Rusty Russell <rusty@rustcorp.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:
+
+ (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