linux-kernel - Re: memset as memzero

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Message-ID: <20070923160750.GO4887@ghostprotocols.net>
Date:	Sun, 23 Sep 2007 13:07:50 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: memset as memzero

Em Sun, Sep 23, 2007 at 11:32:43AM -0400, Dave Jones escreveu:
> On Sat, Sep 22, 2007 at 11:53:53AM -0700, Linus Torvalds wrote:
>  > 
>  > 
>  > On Sat, 22 Sep 2007, Arjan van de Ven wrote:
>  > > 
>  > > it doesn't add value.... memset with a constant 0 is just as fast
>  > > (since the compiler knows it's 0) than any wrapper around it, and the
>  > > syntax around it is otherwise the same.
>  > 
>  > Indeed.
>  > 
>  > The reason we have "clear_page()" is not because the value we're writing 
>  > is constant - that doesn't really help/change anything at all. We could 
>  > have had a "fill_page()" that sets the value to any random byte, it's just 
>  > that zero is the only value that we really care about.
>  > 
>  > So the reason we have "clear_page()" is because the *size* and *alignment* 
>  > is constant and known at compile time, and unlike the value you write, 
>  > that actually matters.
>  > 
>  > So "memzero()" would never really make sense as anything but a syntactic 
>  > wrapper around "memset(x,0,size)". 
> 
> There is one useful argument for memzero (or bzero to give it its proper
> name), and that's that it's impossible to screw up.
> I'm still amazed at how many times I see
> 
> 	memset (x,size,0);
> 
> in various code. So much so, that my editor highlights it now to spot
> it during code review.  As does my mail client.  To be on the safe
> side, I also have a cron job grepping for it in my ~/Mail/commits
> for all the projects I'm interested in.
> 
> It's tragic really just how easy it is to screw it up.

bzero! That is it, its nothing new, just a sane name to something that
is useful to humans, even being of sheer arrogant disdain for machines
as a useless stuff only humans couldn't get right. Yeah, us screw up
pretty much more than them.

- Arnaldo
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