linux-kernel - Re: [PATCH v2 6/7] cmdline: Gives architectures opportunity to use generically defined boot cmdline manipulation

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Message-ID: <8db81511-3f28-4ef1-5e66-188cf7cafad1@csgroup.eu>
Date:   Thu, 25 Mar 2021 12:18:38 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Will Deacon <will@...nel.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, danielwa@...co.com,
        robh@...nel.org, daniel@...pelevich.san-francisco.ca.us,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arch@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 6/7] cmdline: Gives architectures opportunity to use
 generically defined boot cmdline manipulation



Le 03/03/2021 à 18:57, Will Deacon a écrit :
> On Tue, Mar 02, 2021 at 05:25:22PM +0000, Christophe Leroy wrote:
>> Most architectures have similar boot command line manipulation
>> options. This patchs adds the definition in init/Kconfig, gated by
>> CONFIG_HAVE_CMDLINE that the architectures can select to use them.
>>
>> In order to use this, a few architectures will have to change their
>> CONFIG options:
>> - riscv has to replace CMDLINE_FALLBACK by CMDLINE_FROM_BOOTLOADER
>> - architectures using CONFIG_CMDLINE_OVERRIDE or
>> CONFIG_CMDLINE_OVERWRITE have to replace them by CONFIG_CMDLINE_FORCE.
>>
>> Architectures also have to define CONFIG_DEFAULT_CMDLINE.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>   init/Kconfig | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 56 insertions(+)
>>
>> diff --git a/init/Kconfig b/init/Kconfig
>> index 22946fe5ded9..a0f2ad9467df 100644
>> --- a/init/Kconfig
>> +++ b/init/Kconfig
>> @@ -117,6 +117,62 @@ config INIT_ENV_ARG_LIMIT
>>   	  Maximum of each of the number of arguments and environment
>>   	  variables passed to init from the kernel command line.
>>   
>> +config HAVE_CMDLINE
>> +	bool
>> +
>> +config CMDLINE_BOOL
>> +	bool "Default bootloader kernel arguments"
>> +	depends on HAVE_CMDLINE
>> +	help
>> +	  On some platforms, there is currently no way for the boot loader to
>> +	  pass arguments to the kernel. For these platforms, you can supply
>> +	  some command-line options at build time by entering them here.  In
>> +	  most cases you will need to specify the root device here.
> 
> Why is this needed as well as CMDLINE_FROM_BOOTLOADER? IIUC, the latter
> will use CONFIG_CMDLINE if it fails to get anything from the bootloader,
> which sounds like the same scenario.
> 
>> +config CMDLINE
>> +	string "Initial kernel command string"
> 
> s/Initial/Default
> 
> which is then consistent with the rest of the text here.
> 
>> +	depends on CMDLINE_BOOL
> 
> Ah, so this is a bit different and I don't think lines-up with the
> CMDLINE_BOOL help text.
> 
>> +	default DEFAULT_CMDLINE
>> +	help
>> +	  On some platforms, there is currently no way for the boot loader to
>> +	  pass arguments to the kernel. For these platforms, you can supply
>> +	  some command-line options at build time by entering them here.  In
>> +	  most cases you will need to specify the root device here.
> 
> (same stale text)
> 
>> +choice
>> +	prompt "Kernel command line type" if CMDLINE != ""
>> +	default CMDLINE_FROM_BOOTLOADER
>> +	help
>> +	  Selects the way you want to use the default kernel arguments.
> 
> How about:
> 
> "Determines how the default kernel arguments are combined with any
>   arguments passed by the bootloader"
> 
>> +config CMDLINE_FROM_BOOTLOADER
>> +	bool "Use bootloader kernel arguments if available"
>> +	help
>> +	  Uses the command-line options passed by the boot loader. If
>> +	  the boot loader doesn't provide any, the default kernel command
>> +	  string provided in CMDLINE will be used.
>> +
>> +config CMDLINE_EXTEND
> 
> Can we rename this to CMDLINE_APPEND, please? There is code in the tree
> which disagrees about what CMDLINE_EXTEND means, so that will need be
> to be updated to be consistent (e.g. the EFI stub parsing order). Having
> the generic option with a different name means we won't accidentally end
> up with the same inconsistent behaviours.

Argh, yes. Seems like the problem is even larger than that IIUC:

- For ARM it means to append the bootloader arguments to the CONFIG_CMDLINE
- For Powerpc it means to append the CONFIG_CMDLINE to the bootloader arguments
- For SH  it means to append the CONFIG_CMDLINE to the bootloader arguments
- For EFI it means to append the bootloader arguments to the CONFIG_CMDLINE
- For OF it means to append the CONFIG_CMDLINE to the bootloader arguments

So what happens on ARM for instance when it selects CONFIG_OF for instance ?
Or should we consider that EXTEND means APPEND or PREPEND, no matter which ?
Because EXTEND is for instance used for:

	config INITRAMFS_FORCE
		bool "Ignore the initramfs passed by the bootloader"
		depends on CMDLINE_EXTEND || CMDLINE_FORCE


Christophe