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Subject: Re: [RFC PATCH 2/2] init: Allow multi-line output of kernel command
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From:   Joe Perches <joe@perches.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Chenggang Wang <wangchenggang@vivo.com>,
        linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>
Date:   Wed, 20 May 2020 19:09:27 -0700
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On Wed, 2020-05-20 at 18:00 -0700, Andrew Morton wrote:
> On Wed, 20 May 2020 13:36:45 -0700 Joe Perches <joe@perches.com> wrote:
> 
> > On Wed, 2020-05-20 at 21:10 +0900, Sergey Senozhatsky wrote:
> > > On (20/05/19 21:58), Joe Perches wrote:
> > > [..]
> > > > >  Maybe we can
> > > > > use here something rather random and much shorter instead. E.g.
> > > > > 256 chars. Hmm. How 
> > > > 
> > > > 	min(some_max like 132/256, PRINTK_LOG_LINE_MAX)
> > > > 
> > > > would work.
> > > 
> > > An alternative approach would be to do what we do in the
> > > print_modules() (the list of modules which can definitely
> > > be longer than 1K chars).
> > > 
> > > We can split command line in a loop - memchr(pos, ' ') - and
> > > pr_cont() parts of the command line. pr_cont() has overflow
> > > control and it flushes cont buffer before it overflows, so
> > > we should not lose anything.
> > 
> > It doesn't matter much here, but I believe
> > there's an 8k max buffer for pr_cont output.
> > 
> > include/linux/printk.h:#define CONSOLE_EXT_LOG_MAX      8192
> > 
> > Anyway, no worries, it simplifies the loop if
> > done that way.
> 
> I'm wondering if we shold add a kernel puts() (putsk()?  yuk) which can
> puts() a string of any length.
> 
> I'm counting around 150 instances of printk("%s", ...) and pr_foo("%s",
> ...) which could perhaps be converted, thus saving an argument.

I'd expect that it hardly matters.
printk(KERN_CONT "string") works.