Re: [PATCH] init/main.c: Print all command line when boot

[Joe Perches <joe@perches.com>]

On Mon, 2020-05-18 at 20:44 -0700, Andrew Morton wrote:
> On Tue, 19 May 2020 11:29:46 +0800 王程刚 <wangchenggang@vivo.com> wrote:
> 
> > Function pr_notice print max length maybe less than the command line length,
> > need more times to print all.
> > For example, arm64 has 2048 bytes command line length, but printk maximum
> > length is only 1024 bytes.
> 
> I can see why that might be a problem!
> 
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -825,6 +825,16 @@ void __init __weak arch_call_rest_init(void)
> >  	rest_init();
> >  }
> >  
> > +static void __init print_cmdline(void)
> > +{
> > +	const char *prefix = "Kernel command line: ";
> 
> const char prefix[] = "...";
> 
> might generate slightly more efficient code.
> 
> > +	int len = -strlen(prefix);
> 
> hm, tricky.  What the heck does printk() actually return to the caller?
> Seems that we forgot to document this, and there are so many different
> paths which a printk call can take internally that I'm not confident
> that they all got it right!

There is no use of the return value of any pr_<level> or
dev_<level> or netdev_<level) in the kernel.

All the pr_<level> mechanisms (as functions) should return void.
https://lore.kernel.org/lkml/1466739971-30399-1-git-send-email-joe@perches.com/

> > +	len += pr_notice("%s%s\n", prefix, boot_command_line);
> > +	while (boot_command_line[len])
> > +		len += pr_notice("%s\n", &boot_command_line[len]);
> > +}

More likely it'd be better to use a strlen(boot_command_line)
and perhaps do something like print multiple lines with args
using strchr(, ' ') at some largish value, say 132 or 256 chars
maximum per line.