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

[Christophe Leroy]

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@xxxxxxxxxx>
> > ---
> >   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