linux-kernel - Re: [patch cr 2/4] [RFC] syscalls, x86: Add __NR

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Message-ID: <20120203095227.GA13162@elte.hu>
Date:	Fri, 3 Feb 2012 10:52:27 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
	Andrew Vagin <avagin@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber Costa <glommer@...allels.com>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>, Valdis.Kletnieks@...edu
Subject: Re: [patch cr 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v7

* Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Fri, 3 Feb 2012 10:09:29 +0100 Ingo Molnar <mingo@...e.hu> wrote:
> 
> > 
> > * Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> > 
> > > > > +			get_random_bytes(&cookies[i][j],
> > > > > +					 sizeof(cookies[i][j]));
> > > > 
> > > > ugly line break.
> > > > 
> > > 
> > > Why? Looks pretty good to me. But sure I'll change it.
> > 
> > It's ugly because it serves no purpose other than pacifying 
> > checkpatch and makes the code *uglier*.
> 
> No it doesn't.  For 80-col displays the code is *already 
> wrapped*.  And that wrapping to column 0 is vastly worse than 
> the above.

Have you actually checked how this actual line would look like 
in an 80 cols terminal, if not broken up? I have, it's exactly 
80 cols so it looks just fine.

( It was probably broken up when it was longer and then left 
  this way - making things permanently worse not just by the 
  linebreak but also by the unnecessary curly braces around the 
  inner loop. )

But more importantly, even if the line was genuinely longer, how 
many people are looking at things in an 80-col display? By my 
experience, from looking at what kinds of terminals kernel 
people use, it's below 1%. (I was one of the last ones holding 
out because text consoles are so much faster than just about any 
usable xterm app - but I switched to a larger terminal some two 
years ago.)

Shouldnt't we concentrate on the 99% case which gets uglified by 
the systematic linebreaks?

Also, there are clearly cases where breaking the line 
intelligently improves things. Such as:

+               /* An example of output and arguments */
+               printf("pid1: %6d pid2: %6d FD: %2d FILES: %2d VM: %2d FS: %2d "
+                      "SIGHAND: %2d IO: %2d SYSVSEM: %2d INV: %2d\n",
+                      pid1, pid2,
+                      sys_kcmp(pid1, pid2, KCMP_FILE,          fd1, fd2),
+                      sys_kcmp(pid1, pid2, KCMP_FILES,         0, 0),
+                      sys_kcmp(pid1, pid2, KCMP_VM,            0, 0),
+                      sys_kcmp(pid1, pid2, KCMP_FS,            0, 0),
+                      sys_kcmp(pid1, pid2, KCMP_SIGHAND,	0, 0),
+                      sys_kcmp(pid1, pid2, KCMP_IO,            0, 0),
+                      sys_kcmp(pid1, pid2, KCMP_SYSVSEM,	0, 0),
+
+                       /* This one should fail */
+                      sys_kcmp(pid1, pid2, KCMP_TYPES + 1,     0, 0));

this is vastly more readable because the arguments are lined up 
vertically not just at the beginning but nicely tabulated along 
the way.

Oh, and note that 

Breaking lines is a tool that should be used on a case by case 
basis, not a hard limit.

> If we want to increase the standard to (say) 96 cols then 
> fine, I'd be happy with that.  But until we do that we should 
> not create such a gruesome mess for those who use 80 cols.

The kernel has *already* become a gruesome mess for 80 col users 
long ago. That was the main reason why I stopped using 80 col 
terminals two years ago ...

So lets stop the pretense.

> > It's a disease. When checkpatch tells you "this line is too 
> > long" then consider it a code cleanliness warning!
> 
> Well yes, if it can be fixed by other means then great.

Yes it can.

Thanks,

	Ingo
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