linux-kernel - Re: [PATCH] init/main.c: Remove redundant space from saved_command

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Date: Fri, 12 Apr 2024 09:46:34 +0800
From: Yuntao Wang <ytcoode@...il.com>
To: mhiramat@...nel.org
Cc: akpm@...ux-foundation.org,
	arnd@...db.de,
	changbin.du@...wei.com,
	christophe.leroy@...roup.eu,
	geert@...ux-m68k.org,
	jpoimboe@...nel.org,
	kjlx@...pleofstupid.com,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	ndesaulniers@...gle.com,
	peterz@...radead.org,
	tglx@...utronix.de,
	tj@...nel.org,
	ytcoode@...il.com
Subject: Re: [PATCH] init/main.c: Remove redundant space from saved_command_line

On Fri, 12 Apr 2024 08:08:39 +0900, Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> On Thu, 11 Apr 2024 23:29:40 +0800
> Yuntao Wang <ytcoode@...il.com> wrote:
> 
> > On Thu, 11 Apr 2024 23:07:45 +0900, Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:
> > 
> > > On Thu, 11 Apr 2024 09:19:32 +0200
> > > Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > 
> > > > CC Hiramatsu-san (now for real :-)
> > > 
> > > Thanks!
> > > 
> > > > 
> > > > On Thu, Apr 11, 2024 at 6:13 AM Yuntao Wang <ytcoode@...il.com> wrote:
> > > > > extra_init_args ends with a space, so when concatenating extra_init_args
> > > > > to saved_command_line, be sure to remove the extra space.
> > > 
> > > Hi Yuntao,
> > > 
> > > Hmm, if you want to trim the end space, you should trim extra_init_args
> > > itself instead of this adjustment. Also, can you share the example?
> > > 
> > > Thank you,
> > 
> > At first, I also intended to fix this issue as you suggested. However,
> > because both extra_command_line and extra_init_args end with a space,
> > making such a change would require modifications in many places.
> 
> You may just need:
> 
> if (extra_init_args)
> 	strim(extra_init_args);

Okay, I'll post another patch, making the changes as you suggested.

> > That's why I chose this approach instead.
> > 
> > Here are some examples before and after modification:
> > 
> > Before: [    0.829179] Kernel command line: 'console=ttyS0 debug -- bootconfig_arg1 '
> > After:  [    0.032648] Kernel command line: 'console=ttyS0 debug -- bootconfig_arg1'
> > 
> > Before: [    0.757217] Kernel command line: 'console=ttyS0 debug -- bootconfig_arg1  arg1'
> > After:  [    0.068184] Kernel command line: 'console=ttyS0 debug -- bootconfig_arg1 arg1'
> > 
> > In order to make it easier to observe spaces, I added quotes when outputting saved_command_line.
> 
> BTW, is this tailing space harm anything? I don't like a cosmetic change.
> 
> Thank you,

I think this modification is necessary.

If saved_command_line is only used internally in the kernel, having extra
spaces, while not perfect, is acceptable to me. However, since saved_command_line
can be accessed by users through the /proc/cmdline file, having these extra
spaces here and there makes it look too casual.

> > 
> > Note that the first 'before' ends with a space, and there are two spaces between
> > 'bootconfig_arg1' and 'arg1' in the second 'before'.
> > 
> > > > >
> > > > > Signed-off-by: Yuntao Wang <ytcoode@...il.com>
> > > > > ---
> > > > >  init/main.c | 4 +++-
> > > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/init/main.c b/init/main.c
> > > > > index 2ca52474d0c3..cf2c22aa0e8c 100644
> > > > > --- a/init/main.c
> > > > > +++ b/init/main.c
> > > > > @@ -660,12 +660,14 @@ static void __init setup_command_line(char *command_line)
> > > > >                         strcpy(saved_command_line + len, extra_init_args);
> > > > >                         len += ilen - 4;        /* strlen(extra_init_args) */
> > > > >                         strcpy(saved_command_line + len,
> > > > > -                               boot_command_line + initargs_offs - 1);
> > > > > +                               boot_command_line + initargs_offs);
> > > > >                 } else {
> > > > >                         len = strlen(saved_command_line);
> > > > >                         strcpy(saved_command_line + len, " -- ");
> > > > >                         len += 4;
> > > > >                         strcpy(saved_command_line + len, extra_init_args);
> > > > > +                       len += ilen - 4; /* strlen(extra_init_args) */
> > > > > +                       saved_command_line[len-1] = '\0'; /* remove trailing space */
> > > > >                 }
> > > > >         }
> > > > 
> > > > Gr{oetje,eeting}s,
> > > > 
> > > >                         Geert
> > > > 
> > > > -- 
> > > > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg
> > > > 
> > > > In personal conversations with technical people, I call myself a hacker. But
> > > > when I'm talking to journalists I just say "programmer" or something like that.
> > > >                                 -- Linus Torvalds
> > > > 
> > > 
> > > 
> > > -- 
> > > Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@...nel.org>