linux-kernel - Re: IO space memcpy support for userspace.

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Message-ID: <21d7e9970812052230j705fc9bfi4a659378a43ca240@mail.gmail.com>
Date:	Sat, 6 Dec 2008 16:30:24 +1000
From:	"Dave Airlie" <airlied@...il.com>
To:	"Roland McGrath" <roland@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	libc-alpha@...rces.redhat.com
Subject: Re: IO space memcpy support for userspace.

On Sat, Dec 6, 2008 at 6:27 AM, Roland McGrath <roland@...hat.com> wrote:
> There is never going to be something in memcpy that makes any magical
> kernel calls to find out about an address.  That's just loony, sorry.
> memcpy is inlined away by the compiler in good cases.  It's like you'd
> asked for "*ptr" to have magical constraints by the compiler generating
> code to ask the kernel if "ptr" is a special address.  Uh, really?
>

Yeah I didn't think it was a good idea, its what HPUX does, so that
implied it probably wasn't a good idea.

I was just hoping it might help people come up with a good idea.

Dave.

> If you can think of an efficient way to determine it and do what you need,
> then you could write optimized routines that do that in the vDSO perhaps.
>
>
> Thanks,
> Roland
>
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