linux-kernel - Re: [PATCH 1/2] Introduce copy_user_handle

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Message-ID: <alpine.LFD.1.10.0807021930470.18105@woody.linux-foundation.org>
Date:	Wed, 2 Jul 2008 19:35:11 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Vitaly Mayatskikh <v.mayatskih@...il.com>
cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] Introduce copy_user_handle_tail routine

On Wed, 2 Jul 2008, Vitaly Mayatskikh wrote:
> 
> Linus wanted this routine to be extremely dumb.

Well, I wanted it simple and dumb, but not dumber than _necessary_.

I think

	if (cleartail)
		memset(dst,0,len);
	return len;

is basically what we should have at the end. Simple and sweet.

Now, the stuff that comes *before* that point is the "try to fix up one 
byte at a time" thing, which I'd like to be simple and dumb. At least to 
start with.

Of course, I also suspect that *eventually* we might want to make it 
smarter and more complex. For example, while performance isn't a primary 
issue, we might want to eventually avoid having to do _two_ faults (once 
in the fast unrolled or word-at-a-time loop, and once in the byte-for-byte 
one), by limiting the byte-for-byte one to be within a page, but that 
would be a "future enhancement" thing.

		Linus
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