[PATCH v2] powerpc: Support CMDLINE_EXTEND

[Chris Packham]

On Thu, 2019-08-01 at 08:14 +0200, Christophe Leroy wrote:
> 
> Le 01/08/2019 à 04:12, Chris Packham a écrit :
> > 
> > Bring powerpc in line with other architectures that support
> > extending or
> > overriding the bootloader provided command line.
> > 
> > The current behaviour is most like CMDLINE_FROM_BOOTLOADER where
> > the
> > bootloader command line is preferred but the kernel config can
> > provide a
> > fallback so CMDLINE_FROM_BOOTLOADER is the default. CMDLINE_EXTEND
> > can
> > be used to append the CMDLINE from the kernel config to the one
> > provided
> > by the bootloader.
> > 
> > Signed-off-by: Chris Packham <chris.packham at alliedtelesis.co.nz>
> > ---
> > While I'm at it does anyone think it's worth getting rid of the
> > default CMDLINE
> > value if CMDLINE_BOOL and maybe CMDLINE_BOOL? Every defconfig in
> > the kernel
> > that sets CMDLINE_BOOL=y also sets CMDLINE to something other than
> > "console=ttyS0,9600 console=tty0 root=/dev/sda2". Removing
> > CMDLINE_BOOL and
> > unconditionally setting the default value of CMDLINE to "" would
> > clean up the
> > Kconfig even more.
> Note 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co
> mmit/?id=cbe46bd4f5104552b612505b73d366f66efc2341 
> which is already a step forward.
> 
> I guess that default is for users selecting this option manually to
> get 
> a first sensitive CMDLINE. But is it really worth it ?
> 

I'm not even sure if it is working as intended right now. Even without
my changes if I use menuconfig and select CMDLINE_BOOL I end up with 
CONFIG_CMDLINE="" in the resulting .config.

> > 
> > 
> > Changes in v2:
> > - incorporate ideas from Christope's patch https://patchwork.ozlabs
> > .org/patch/1074126/
> > 
> >   arch/powerpc/Kconfig            | 20 +++++++++++++++++++-
> >   arch/powerpc/kernel/prom_init.c | 26 +++++++++++++++++++++++++-
> >   2 files changed, 44 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index 77f6ebf97113..d413fe1b4058 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -852,15 +852,33 @@ config CMDLINE
> >   	  some command-line options at build time by entering
> > them here.  In
> >   	  most cases you will need to specify the root device
> > here.
> >   
> > +choice
> > +	prompt "Kernel command line type" if CMDLINE != ""
> > +	default CMDLINE_FROM_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
> > +	bool "Extend bootloader kernel arguments"
> > +	help
> > +	  The command-line arguments provided by the boot loader
> > will be
> > +	  appended to the default kernel command string.
> > +
> >   config CMDLINE_FORCE
> >   	bool "Always use the default kernel command string"
> > -	depends on CMDLINE_BOOL
> >   	help
> >   	  Always use the default kernel command string, even if
> > the boot
> >   	  loader passes other arguments to the kernel.
> >   	  This is useful if you cannot or don't want to change
> > the
> >   	  command-line options your boot loader passes to the
> > kernel.
> >   
> > +endchoice
> > +
> >   config EXTRA_TARGETS
> >   	string "Additional default image types"
> >   	help
> > diff --git a/arch/powerpc/kernel/prom_init.c
> > b/arch/powerpc/kernel/prom_init.c
> > index 514707ef6779..df29f141dbd2 100644
> > --- a/arch/powerpc/kernel/prom_init.c
> > +++ b/arch/powerpc/kernel/prom_init.c
> > @@ -310,6 +310,25 @@ static size_t __init prom_strlcpy(char *dest,
> > const char *src, size_t size)
> >   	return ret;
> >   }
> >   
> > +static size_t __init prom_strlcat(char *dest, const char *src,
> > size_t count)
> > +{
> > +	size_t dsize = prom_strlen(dest);
> > +	size_t len = prom_strlen(src);
> > +	size_t res = dsize + len;
> > +
> > +	/* This would be a bug */
> > +	BUG_ON(dsize >= count);
> Has you pointed in another mail, BUG_ON() should be avoided here.
> I guess if the destination is already full, just return count:
> 
> if (dsize >= count)
> 	return count;
> 

Will fix in v3.

> > 
> > +
> > +	dest += dsize;
> > +	count -= dsize;
> > +	if (len >= count)
> > +		len = count-1;
> > +	memcpy(dest, src, len);
> > +	dest[len] = 0;
> > +	return res;
> > +
> > +}
> > +
> >   #ifdef CONFIG_PPC_PSERIES
> >   static int __init prom_strtobool(const char *s, bool *res)
> >   {
> > @@ -761,8 +780,13 @@ static void __init early_cmdline_parse(void)
> >   	p = prom_cmd_line;
> >   	if ((long)prom.chosen > 0)
> >   		l = prom_getprop(prom.chosen, "bootargs", p,
> > COMMAND_LINE_SIZE-1);
> The above is pointless in case CONFIG_CMDLINE_FORCE is selected.
> 

Will fix in v3.

> > 
> > -	if (IS_ENABLED(CONFIG_CMDLINE_BOOL) && (l <= 0 || p[0] ==
> > '\0')) /* dbl check */
> > +
> > +	if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || l <= 0 || p[0] ==
> > '\0')
> >   		prom_strlcpy(prom_cmd_line, CONFIG_CMDLINE,
> > sizeof(prom_cmd_line));
> If we can ensure that prom_cmd_line remains empty when 
> CONFIG_CMDLINE_FORCE is selected (see above comment), then 
> prom_strlcat() can be used in lieu of prom_strlcpy()
> 
> > 
> > +	else if (IS_ENABLED(CONFIG_CMDLINE_EXTEND))
> > +		prom_strlcat(prom_cmd_line, " " CONFIG_CMDLINE,
> > +			     sizeof(prom_cmd_line));
> > +
> >   	prom_printf("command line: %s\n", prom_cmd_line);
> >   
> >   #ifdef CONFIG_PPC64
> > 
> Christophe